Packaging, Releasing, and Daily Development
This chapter is about how free software projects package and
release their software, and how overall development patterns organize
around those goals.
A major difference between open source projects and proprietary
ones is the lack of centralized control over the development team.
When a new release is being prepared, this difference is especially
stark: a corporation can ask its entire development team to focus on
an upcoming release, putting aside new feature development and
non-critical bug fixing until the release is done. Volunteer groups
are not so monolithic. People work on the project for all sorts of
reasons, and those not interested in helping with a given release
still want to continue regular development work while the release is
going on. Because development doesn't stop, open source release
processes tend to take longer, but be less disruptive, than commercial
release processes. It's a bit like highway repair. There are two
ways to fix a road: you can shut it down completely, so that a repair
crew can swarm all over it at full capacity until the problem is
solved, or you can work on a couple of lanes at a time, while leaving the
others open to traffic. The first way is very efficient for
the repair crew, but not for anyone else—the road is
entirely shut down until the job is done. The second way involves
much more time and trouble for the repair crew (now they have to work
with fewer people and less equipment, in cramped conditions, with
flaggers to slow and direct traffic, etc.), but at least the road
remains useable, albeit not at full capacity.
Open source projects tend to work the second way. In fact, for
a mature piece of software with several different release lines being
maintained simultaneously, the project is sort of in a permanent state
of minor road repair. There are always a couple of lanes closed; a
consistent but low level of background inconvenience is always being
tolerated by the development group as a whole, so that releases get
made on a regular schedule.
The model that makes this possible generalizes to more than just
releases. It's the principle of parallelizing tasks that are not
mutually interdependent—a principle that is by no means unique
to open source development, of course, but one which open source
projects implement in their own particular way. They cannot afford to
annoy either the roadwork crew or the regular traffic too much, but
they also cannot afford to have people dedicated to standing by the
orange cones and flagging traffic along. Thus they gravitate toward
processes that have flat, constant levels of administrative overhead,
rather than peaks and valleys. Volunteers are generally willing to
work with small but consistent amounts of inconvenience; the
predictability allows them to come and go without worrying about
whether their schedule will clash with what's happening in the
project. But if the project were subject to a master schedule in
which some activities excluded other activities, the result would be a
lot of developers sitting idle a lot of the time—which would be
not only inefficient but boring, and therefore dangerous, in that a
bored developer is likely to soon be an ex-developer.
Release work is usually the most noticeable non-development task
that happens in parallel with development, so the methods described in
the following sections are geared mostly toward enabling releases.
However, note that they also apply to other parallelizable tasks, such
as translations and internationalization, broad API changes made
gradually across the entire code base, etc.
Release Numbering
Before we talk about how to make a release, let's look at how to
name releases, which requires knowing what releases actually mean to
users. A release means that:
Old bugs have been fixed. This is probably the one
thing users can count on being true of every release.
New bugs have been added. This too can usually
be counted on, except sometimes in the case of security
releases or other one-offs (see
later in this chapter).
New features may have been added.
New configuration options may have been added, or
the meanings of old options may have changed subtly. The
installation procedures may have changed slightly since
the last release too, though one always hopes not.
Incompatible changes may have been introduced, such
that the data formats used by older versions of the
software are no longer useable without undergoing some
sort of (possibly manual) one-way conversion step.
As you can see, not all of these are good things. This is why
experienced users approach new releases with some trepidation,
especially when the software is mature and was already mostly doing
what they wanted (or thought they wanted). Even the arrival of new
features is a mixed blessing, in that it may mean the software
will now behave in unexpected ways.
The purpose of release numbering, therefore, is twofold:
obviously the numbers should unambiguously communicate the ordering of
releases (i.e., by looking at any two releases' numbers, one can know
which came later), but also they should indicate as compactly as
possible the degree and nature of the changes in the release.
All that in a number? Well, more or less, yes. Release
numbering strategies are one of the oldest bikeshed discussions around
(see in
), and the world is
unlikely to settle on a single, complete standard anytime soon.
However, a few good strategies have emerged, along with one
universally agreed-on principle: be consistent.
Pick a numbering scheme, document it, and stick with it. Your users
will thank you.
Release Number Components
This section describes the formal conventions of release
numbering in detail, and assumes very little prior knowledge. It is
intended mainly as a reference. If you're already familiar with these
conventions, you can skip this section.
Release numbers are groups of digits separated by dots:
Scanley 2.3
Singer 5.11.4
...and so on. The dots are not decimal
points, they are merely separators; "5.3.9" would be followed by
"5.3.10". A few projects have occasionally hinted otherwise, most
famously the Linux kernel with its "0.95", "0.96"... "0.99" sequence
leading up to Linux 1.0, but the convention that the dots are not
decimals is now firmly established and should be considered a
standard. There is no limit to the number of components (digit
portions containing no dots), but most projects do not go beyond three
or four. The reasons why will become clear later.
In addition to the numeric components, projects sometimes tack
on a descriptive label such as "Alpha" or "Beta" (see
), for example:
Scanley 2.3.0 (Alpha)
Singer 5.11.4 (Beta)
An Alpha or Beta qualifier means that this
release precedes a future release that will have
the same number without the qualifier. Thus, "2.3.0 (Alpha)"
leads eventually to "2.3.0". In order to allow several such candidate
releases in a row, the qualifiers themselves can have meta-qualifiers.
For example, here is a series of releases in the order that they would
be made available to the public:
Scanley 2.3.0 (Alpha 1)
Scanley 2.3.0 (Alpha 2)
Scanley 2.3.0 (Beta 1)
Scanley 2.3.0 (Beta 2)
Scanley 2.3.0 (Beta 3)
Scanley 2.3.0
Notice that when it has the "Alpha" qualifier, Scanley "2.3" is
written as "2.3.0". The two numbers are equivalent—trailing
all-zero components can always be dropped for brevity—but when a
qualifier is present, brevity is out the window anyway, so one might
as well go for completeness instead.
Other qualifiers in semi-regular use include "Stable",
"Unstable", "Development", and "RC" (for "Release Candidate"). The
most widely used ones are still "Alpha" and "Beta", with "RC" running
a close third place, but note that "RC" always includes a numeric
meta-qualifier. That is, you don't release
"Scanley 2.3.0 (RC)", you release
"Scanley 2.3.0 (RC 1)", followed by RC2, etc.
Those three labels, "Alpha", "Beta", and "RC", are pretty widely
known now, and I don't recommend using any of the others, even though
the others might at first glance seem like better choices because they
are normal words, not jargon. But people who install software from
releases are already familiar with the big three, and there's no
reason to do things gratuitously differently from the way everyone
else does them.
Although the dots in release numbers are not decimal points,
they do indicate place-value significance. All "0.X.Y" releases
precede "1.0" (which is equivalent to "1.0.0", of course). "3.14.158"
immediately precedes "3.14.159", and non-immediately precedes
"3.14.160" as well as "3.15.anything", and so.
A consistent release numbering policy enables a user to look at
two release numbers for the same piece of software and tell, just from
the numbers, the important differences between those two releases. In
a typical three-component system, the first component is
the major number, the second is
the minor number, and the third is the
micro number. For example, release
"2.10.17" is the seventeenth micro release in the tenth minor release
line within the second major release series. The words "line" and
"series" are used informally here, but they mean what one would
expect. A major series is simply all the releases that share the same
major number, and a minor series (or minor line) consists of all the releases
that share the same minor and major number. That
is, "2.4.0" and "3.4.1" are not in the same minor series,
even though they both have "4" for their minor number; on the other
hand, "2.4.0" and "2.4.2" are in the same minor line, though they are
not adjacent if "2.4.1" was released between them.
The meanings of these numbers are exactly what you'd expect: an
increment of the major number indicates that major changes happened;
an increment of the minor number indicates minor changes; and an
increment of the micro number indicates really trivial changes. Some
projects add a fourth component, usually called
the patch number, for especially
fine-grained control over the differences between their releases
(confusingly, other projects use "patch" as a synonym for "micro" in a
three-component system). There are also projects that use the last
component as a build number, incremented
every time the software is built and representing no change other than
that build. This helps the project link every bug report with a
specific build, and is probably most useful when binary packages are
the default method of distribution.
Although there are many different conventions for how many
components to use, and what the components mean, the differences tend
to be minor—you get a little leeway, but not a lot. The next
two sections discuss some of the most widely used conventions.
The Simple Strategy
Most projects have rules about what kinds of changes are allowed
into a release if one is only incrementing the micro number, different
rules for the minor number, and still different ones for the major
number. There is no set standard for these rules yet, but here I will
describe a policy that has been used successfully by multiple
projects. You may want to just adopt this policy in your own
project, but even if you don't, it's still a good example of the kind
of information release numbers should convey. This policy is adapted
from the numbering system used by the APR project, see
.
Changes to the micro number only (that is, changes
within the same minor line) must be both forward- and
backward-compatible. That is, the changes should be bug
fixes only, or very small enhancements to existing
features. New features should not be introduced in a
micro release.
Changes to the minor number (that is, within the
same major line) must be backward-compatible, but not
necessarily forward-compatible. It's normal to introduce
new features in a minor release, but usually not too many
new features at once.
Changes to the major number mark compatibility
boundaries. A new major release can be forward- and
backward-incompatible. A major release is expected to
have new features, and may even have entire new feature
sets.
What backward-compatible
and forward-compatible mean, exactly, depends on
what your software does, but in context they are usually not open to
much interpretation. For example, if your project is a client/server
application, then "backward-compatible" means that upgrading the
server to 2.6.0 should not cause any existing 2.5.4 clients to lose
functionality or behave differently than they did before (except for
bugs that were fixed, of course). On the other hand, upgrading one of
those clients to 2.6.0, along with the server, might
make new functionality available for that client,
functionality that 2.5.4 clients don't know how to take advantage of.
If that happens, then the upgrade is not
"forward-compatible": clearly you can't now downgrade that client
back to 2.5.4 and keep all the functionality it had at 2.6.0, since
some of that functionality was new in 2.6.0.
This is why micro releases are essentially for bug fixes only.
They must remain compatible in both directions: if you upgrade from
2.5.3 to 2.5.4, then change your mind and downgrade back to 2.5.3, no
functionality should be lost. Of course, the bugs fixed in 2.5.4
would reappear after the downgrade, but you wouldn't lose any
features, except insofar as the restored bugs prevent the use of some
existing features.
Client/server protocols are just one of many possible
compatibility domains. Another is data formats: does the software
write data to permanent storage? If so, the formats it reads and
writes need to follow the compatibility guidelines promised by the
release number policy. Version 2.6.0 needs to be able to read the
files written by 2.5.4, but may silently upgrade the format to
something that 2.5.4 cannot read, because the ability to downgrade is
not required across a minor number boundary. If your project
distributes code libraries for other programs to use, then APIs are a
compatibility domain too: you must make sure that source and binary
compatibility rules are spelled out in such a way that the informed
user need never wonder whether or not it's safe to upgrade in place.
She will be able to look at the numbers and know instantly.
In this system, you don't get a chance for a fresh start until
you increment the major number. This can often be a real
inconvenience: there may be features you wish to add, or protocols
that you wish to redesign, that simply cannot be done while
maintaining compatibility. There's no magic solution to this, except
to try to design things in an extensible way in the first place (a
topic easily worth its own book, and certainly outside the scope of
this one). But publishing a release compatibility policy, and
adhering to it, is an inescapable part of distributing software. One
nasty surprise can alienate a lot of users. The policy just described
is good partly because it's already quite widespread, but also because
it's easy to explain and to remember, even for those not already familiar
with it.
It is generally understood that these rules do not apply to
pre-1.0 releases (although your release policy should probably state
so explicitly, just to be clear). A project that is still in initial
development can release 0.1, 0.2, 0.3, and so on in sequence, until
it's ready for 1.0, and the differences between those releases can be
arbitrarily large. Micro numbers in pre-1.0 releases are optional.
Depending on the nature of your project and the differences between
the releases, you might find it useful to have 0.1.0, 0.1.1, etc., or
you might not. Conventions for pre-1.0 release numbers are fairly
loose, mainly because people understand that strong compatibility
constraints would hamper early development too much, and because early
adopters tend to be forgiving anyway.
Remember that all these injunctions only apply to this
particular three-component system. Your project could easily come up
with a different three-component system, or even decide it doesn't
need such fine granularity and use a two-component system instead.
The important thing is to decide early, publish exactly what the
components mean, and stick to it.
The Even/Odd Strategy
Some projects use the parity of the minor number component to
indicate the stability of the software: even means stable, odd means
unstable. This applies only to the minor number, not the major and
micro numbers. Increments in the micro number still indicate bug
fixes (no new features), and increments in the major number still
indicate big changes, new feature sets, etc.
The advantage of the even/odd system, which has been used by the
Linux kernel project among others, is that it offers a way to release
new functionality for testing without subjecting production users to
potentially unstable code. People can see from the numbers that
"2.4.21" is okay to install on their live web server, but that "2.5.1"
should probably stay confined to home workstation experiments. The
development team handles the bug reports that come in from the
unstable (odd-minor-numbered) series, and when things start to settle
down after some number of micro releases in that series, they
increment the minor number (thus making it even), reset the micro
number back to "0", and release a presumably stable package.
This system preserves, or at least, does not conflict with, the
compatibility guidelines given earlier. It simply overloads the minor
number with some extra information. This forces the minor number to
be incremented about twice as often as would otherwise be necessary,
but there's no great harm in that. The even/odd system is probably
best for projects that have very long release cycles, and which by
their nature have a high proportion of conservative users who value
stability above new features. It is not the only way to get new
functionality tested in the wild, however.
later in this chapter describes another, perhaps more common,
method of releasing potentially unstable code to the public, marked so
that people have an idea of the risk/benefit trade-offs immediately on
seeing the release's name.
Release Branches
From a developer's point of view, a free software project is in
a state of continuous release. Developers usually run the latest
available code at all times, because they want to spot bugs, and
because they follow the project closely enough to be able to stay away
from currently unstable areas of the feature space. They often update
their copy of the software every day, sometimes more than once a day,
and when they check in a change, they can reasonably expect that every
other developer will have it within 24 hours.
How, then, should the project make a formal release? Should it
simply take a snapshot of the tree at a moment in time, package it up,
and hand it to the world as, say, version "3.5.0"? Common sense says
no. First, there may be no moment in time when the entire development
tree is clean and ready for release. Newly-started features could be
lying around in various states of completion. Someone might have
checked in a major change to fix a bug, but the change could be
controversial and under debate at the moment the snapshot is taken.
If so, it wouldn't work to simply delay the snapshot until the debate
ends, because another, unrelated debate could start in the meantime,
and then you'd have wait for that one to end too.
This process is not guaranteed to halt.
In any case, using full-tree snapshots for releases would
interfere with ongoing development work, even if the tree could be put
into a releasable state. Say this snapshot is going to be "3.5.0";
presumably, the next snapshot would be "3.5.1", and would contain
mostly fixes for bugs found in the 3.5.0 release. But if both are
snapshots from the same tree, what are the developers supposed to do
in the time between the two releases? They can't be adding new
features; the compatibility guidelines prevent that. But not everyone
will be enthusiastic about fixing bugs in the 3.5.0 code. Some people
may have new features they're trying to complete, and will become
irate if they are forced to choose between sitting idle and working on
things they're not interested in, just because the project's release
processes demand that the development tree remain unnaturally
quiescent.
The solution to these problems is to always use
a release branch. A release branch is just a
branch in the version control system (see
), on which the code
destined for this release can be isolated from mainline development.
The concept of release branches is certainly not original to free
software; many commercial development organizations use them too.
However, in commercial environments, release branches are sometimes
considered a luxury—a kind of formal "best practice" that can,
in the heat of a major deadline, be dispensed with while everyone on
the team scrambles to stabilize the main tree.
Release branches are pretty much required in open source
projects, however. I have seen projects do releases without them, but
it has always resulted in some developers sitting idle while
others—usually a minority—work on getting the release out
the door. The result is usually bad in several ways. First, overall
development momentum is slowed. Second, the release is of poorer
quality than it needed to be, because there were only a few people
working on it, and they were hurrying to finish so everyone else could
get back to work. Third, it divides the development team
psychologically, by setting up a situation in which different types of
work interfere with each other unnecessarily. The developers sitting
idle would probably be happy to contribute some
of their attention to a release branch, as long as that were a choice
they could make according to their own schedules and interests. But
without the branch, their choice becomes "Do I participate in the
project today or not?" instead of "Do I work on the release today, or
work on that new feature I've been developing in the mainline
code?"
Mechanics of Release Branches
The exact mechanics of creating a release branch depend on your
version control system, of course, but the general concepts are the
same in most systems. A branch usually sprouts from another branch or
from the trunk. Traditionally, the trunk is where mainline
development goes on, unfettered by release constraints. The first
release branch, the one leading to the "1.0" release, sprouts off the
trunk. In CVS, the branch command would be something like this
$ cd trunk-working-copy
$ cvs tag -b RELEASE_1_0_X
or in Subversion, like this:
$ svn copy http://.../repos/trunk http://.../repos/branches/1.0.x
(All these examples assume a three-component release numbering
system. While I can't show the exact commands for every version
control system, I'll give examples in CVS and Subversion and hope that
the corresponding commands in other systems can be deduced from those
two.)
Notice that we created branch "1.0.x" (with a literal "x")
instead of "1.0.0". This is because the same minor line—i.e.,
the same branch—will be used for all the micro releases in that
line. The actual process of stabilizing the branch for release is
covered in
later in this chapter. Here we are
concerned just with the interaction between the version control system
and the release process. When the release branch is stabilized and
ready, it is time to tag a snapshot from the branch:
$ cd RELEASE_1_0_X-working-copy
$ cvs tag RELEASE_1_0_0
or
$ svn copy http://.../repos/branches/1.0.x http://.../repos/tags/1.0.0
That tag now represents the exact state of the project's source
tree in the 1.0.0 release (this is useful in case anyone ever needs to
get an old version after the packaged distributions and binaries have
been taken down). The next micro release in the same line is likewise
prepared on the 1.0.x branch, and when it is ready, a tag is made for
1.0.1. Lather, rinse, repeat for 1.0.2, and so on. When it's time to
start thinking about a 1.1.x release, make a new branch from
trunk:
$ cd trunk-working-copy
$ cvs tag -b RELEASE_1_1_X
or
$ svn copy http://.../repos/trunk http://.../repos/branches/1.1.x
Maintenance can continue in parallel along both 1.0.x and 1.1.x,
and releases can be made independently from both lines. In fact, it
is not unusual to publish near-simultaneous releases from two
different lines. The older series is recommended for more
conservative site administrators, who may not want to make the big
jump to (say) 1.1 without careful preparation. Meanwhile, more
adventurous people usually take the most recent release on the highest
line, to make sure they're getting the latest features, even at the
risk of greater instability.
This is not the only release branch strategy, of course. In
some circumstances it may not even be the best, though it's worked out
pretty well for projects I've been involved in. Use any strategy that
seems to work, but remember the main points: the purpose of a release
branch is to isolate release work from the fluctuations of daily
development, and to give the project a physical entity around which to
organize its release process. That process is described in detail in
the next section.
Stabilizing a Release
Stabilization is the process of getting a
release branch into a releasable state; that is, of deciding which
changes will be in the release, which will not, and shaping the branch
content accordingly.
There's a lot of potential grief contained in that word,
"deciding". The last-minute feature rush is a familiar phenomenon in
collaborative software projects: as soon as developers see that a
release is about to happen, they scramble to finish their current
changes, in order not to miss the boat. This, of course, is the exact
opposite of what you want at release time. It would be much better
for people to work on features at a comfortable pace, and not worry
too much about whether their changes make it into this release or the
next one. The more changes one tries to cram into a release at the
last minute, the more the code is destabilized, and (usually) the more
new bugs are created.
Most software engineers agree in theory on rough criteria for
what changes should be allowed into a release line during its
stabilization period. Obviously, fixes for severe bugs can go in,
especially for bugs without workarounds. Documentation updates are
fine, as are fixes to error messages (except when they are considered
part of the interface and must remain stable). Many projects also
allow certain kinds of low-risk or non-core changes to go in during
stabilization, and may have formal guidelines for measuring risk. But
no amount of formalization can obviate the need for human judgement.
There will always be cases where the project simply has to make a
decision about whether a given change can go into a release. The
danger is that since each person wants to see their own favorite
changes admitted into the release, then there will be plenty of people
motivated to allow changes, and not enough people motivated to bar
them.
Thus, the process of stabilizing a release is mostly about
creating mechanisms for saying "no". The trick for open source
projects, in particular, is to come up with ways of saying "no" that
won't result in too many hurt feelings or disappointed developers, and
also won't prevent deserving changes from getting into the release.
There are many different ways to do this. It's pretty easy to design
systems that satisfy these criteria, once the team has focused on them
as the important criteria. Here I'll briefly describe two of the most
popular systems, at the extreme ends of the spectrum, but don't let
that discourage your project from being creative. Plenty of other
arrangements are possible; these are just two that I've seen work in
practice.
Dictatorship by Release Owner
The group agrees to let one person be the release
owner. This person has final say over what changes make
it into the release. Of course, it is normal and expected for there
to be discussions and arguments, but in the end the group must grant
the release owner sufficient authority to make final decisions. For
this system to work, it is necessary to choose someone with the
technical competence to understand all the changes, and the social
standing and people skills to navigate the discussions leading up to
the release without causing too many hurt feelings.
A common pattern is for the release owner to say "I don't think
there's anything wrong with this change, but we haven't had enough
time to test it yet, so it shouldn't go into this release." It helps
a lot if the release owner has broad technical knowledge of the
project, and can give reasons why the change could be potentially
destabilizing (for example, its interactions with other parts of the
software, or portability concerns). People will sometimes ask such
decisions to be justified, or will argue that a change is not as risky
as it looks. These conversations need not be confrontational, as long
as the release owner is able to consider all the arguments objectively
and not reflexively dig in his heels.
Note that the release owner need not be the same person as the
project leader (in cases where there is a project leader at all; see
in ). In fact,
sometimes it's
good to make sure they're not the same person.
The skills that make a good development leader are not necessarily the
same as those that make a good release owner. In something as
important as the release process, it may be wise to have someone
provide a counterbalance to the project leader's judgement.
Contrast the release owner role with the less dictatorial role
described in
later
in this chapter.
Change Voting
At the opposite extreme from dictatorship by release owner,
developers can simply vote on which changes to include in the release.
However, since the most important function of release stabilization is
to exclude changes, it's important to design the
voting system in such a way that getting a change into the release
involves positive action by multiple developers. Including a change
should need more than just a simple majority (see in
). Otherwise,
one vote for and none against a given change would suffice to get it
into the release, and an
unfortunate dynamic would be set up whereby each developer would vote
for her own changes, yet would be reluctant to vote against others'
changes, for fear of possible retaliation. To avoid this, the system
should be arranged such that subgroups of developers must act in
cooperation to get any change into the release. This not only means
that more people review each change, it also makes any individual
developer less hesitant to vote against a change, because she knows
that no particular one among those who voted for it would take her
vote against as a personal affront. The greater the number of people
involved, the more the discussion becomes about the change and less
about the individuals.
The system we use in the Subversion project seems to have struck
a good balance, so I'll recommend it here. In order for a change to
be applied to the release branch, at least three developers must vote
in favor of it, and none against. A single "no" vote is enough to
stop the change from being included; that is, a "no" vote in a release
context is equivalent to a veto (see ).
Naturally, any such vote must be accompanied by a justification, and
in theory the veto could be overridden if enough people feel it is
unreasonable and force a special vote over it. In practice, this has
never happened, and I don't expect that it ever will. People are
conservative around releases anyway, and when someone feels strongly
enough to veto the inclusion of a change, there's usually a good
reason for it.
Because the release procedure is deliberately biased toward
conservatism, the justifications offered for vetoes are sometimes
procedural rather than technical. For example, a person may feel that
a change is well-written and unlikely to cause any new bugs, but vote
against its inclusion in a micro release simply because it's too
big—perhaps it adds a new feature, or in some subtle way fails
to fully follow the compatibility guidelines. I've occasionally even
seen developers veto something because they simply had a gut feeling
that the change needed more testing, even though they couldn't spot
any bugs in it by inspection. People grumbled a little bit, but the
vetoes stood and the change was not included in the release (I don't
remember if any bugs were found in later testing or not,
though).
Managing collaborative release stabilization
If your project chooses a change voting system, it is imperative
that the physical mechanics of setting up ballots and casting votes be
as convenient as possible. Although there is plenty of open source
electronic voting software available, in practice the easiest thing to
do is just to set up a text file in the release branch,
called STATUS or VOTES or
something like that. This file lists each proposed change—any
developer can propose a change for inclusion—along with all the
votes for and against it, plus any notes or comments. (Proposing a
change doesn't necessarily mean voting for it, by the way, although
the two often go together.) An entry in such a file might look like
this:
* r2401 (issue #49)
Prevent client/server handshake from happening twice.
Justification:
Avoids extra network turnaround; small change and easy to review.
Notes:
This was discussed in http://.../mailing-lists/message-7777.html
and other messages in that thread.
Votes:
+1: jsmith, kimf
-1: tmartin (breaks compatibility with some pre-1.0 servers;
admittedly, those servers are buggy, but why be
incompatible if we don't have to?)
In this case, the change acquired two positive votes, but was
vetoed by tmartin, who gave the reason for the veto in a parenthetical
note. The exact format of the entry doesn't matter; whatever your
project settles on is fine—perhaps tmartin's explanation for the
veto should go up in the "Notes:" section, or perhaps the change
description should get a "Description:" header to match the other
sections. The important thing is that all the information needed to
evaluate the change be reachable, and that the mechanism for casting
votes be as lightweight as possible. The proposed change is referred
to by its revision number in the repository (in this case a single
revision, r2401, although a proposed change could just as easily
consist of multiple revisions). The revision is assumed to refer to a
change made on the trunk; if the change were already on the release
branch, there would be no need to vote on it. If your version control
system doesn't have an obvious syntax for referring to individual
changes, then the project should make one up. For voting to be
practical, each change under consideration must be unambiguously
identifiable.
Those proposing or voting for a change are responsible for
making sure it applies cleanly to the release branch, that is, applies
without conflicts (see ).
If there are conflicts, then the entry should either point to an
adjusted patch that does apply cleanly, or to a temporary branch that
holds an adjusted version of the change, for example:
* r13222, r13223, r13232
Rewrite libsvn_fs_fs's auto-merge algorithm
Justification:
unacceptable performance (>50 minutes for a small commit) in
a repository with 300,000 revisions
Branch:
1.1.x-r13222@13517
Votes:
+1: epg, ghudson
That example is taken from real life; it comes from the
STATUS file for the Subversion 1.1.4 release
process. Notice how it uses the original revisions as canonical
handles on the change, even though there is also a branch with a
conflict-adjusted version of the change (the branch also combines the
three trunk revisions into one, r13517, to make it easier to merge the
change into the release, should it get approval). The original
revisions are provided because they're still the easiest entity to
review, since they have the original log messages. The temporary
branch wouldn't have those log messages; in order to avoid duplication
of information (see
in
), the
branch's log message for r13517 should simply say "Adjust r13222,
r13223, and r13232 for backport to 1.1.x branch." All other
information about the changes can be chased down at their original
revisions.
Release manager
The actual process of merging (see
) approved changes into the
release branch can be performed by any developer. There does not need
to be one person whose job it is to merge changes; if there are a lot
of changes, it can be better to spread the burden around.
However, although both voting and merging happen in a
decentralized fashion, in practice there are usually one or two people
driving the release process. This role is sometimes formally blessed
as release manager, but it is quite different
from a release owner (see
earlier
in this chapter) who has
final say over the changes. Release managers keep track of how many
changes are currently under consideration, how many have been
approved, how many seem likely to be approved, etc. If they sense
that important changes are not getting enough attention, and might be
left out of the release for lack of votes, they will gently nag other
developers to review and vote. When a batch of changes are approved,
these people will often take it upon themselves to merge them into the
release branch; it's fine if others leave that task to them, as
long as everyone understands that they are not obligated to do all the
work unless they have explicitly committed to it. When the time comes
to put the release out the door (see
later in this chapter), the release managers
also take care of the logistics of creating the final release
packages, collecting digital signatures, uploading the packages, and
making the public announcement.
Packaging
The canonical form for distribution of free software is as
source code. This is true regardless of whether the software normally
runs in source form (i.e., can be interpreted, like Perl, Python, PHP,
etc.) or needs to be compiled first (like C, C++, Java, etc.). With
compiled software, most users will probably not compile the sources
themselves, but will instead install from pre-built binary packages
(see
later in this chapter). However, those binary
packages are still derived from a master source distribution. The
point of the source package is to unambiguously define the release.
When the project distributes "Scanley 2.5.0", what it means,
specifically, is "The tree of source code files that, when compiled
(if necessary) and installed, produces Scanley 2.5.0."
There is a fairly strict standard for how source releases
should look. One will occasionally see deviations from this standard,
but they are the exception, not the rule. Unless there is a compelling
reason to do otherwise, your project should follow this standard
too.
Format
The source code should be shipped in the standard formats for
transporting directory trees. For Unix and Unix-like operating
systems, the convention is to use TAR format, compressed
by compress, gzip,
bzip or bzip2. For MS Windows,
the standard method for distributing directory trees
is zip format, which happens to do compression
as well, so there is no need to compress the archive after creating
it.
TAR Files
TAR stands for "Tape ARchive",
because tar format represents a directory tree as a linear data
stream, which makes it ideal for saving directory trees to tape.
The same property also makes it the standard for distributing
directory trees as a single file. Producing compressed tar files
(or tarballs) is pretty easy. On some
systems, the tar command can produce a
compressed archive itself; on others, a separate compression
program is used.
Name and Layout
The name of the package should consist of the software's name
plus the release number, plus the format suffixes appropriate for the
archive type. For example, Scanley 2.5.0, packaged for Unix using GNU
Zip (gzip) compression, would look like this:
scanley-2.5.0.tar.gz
or for Windows using zip compression:
scanley-2.5.0.zip
Either of these archives, when unpacked, should create a single
new directory tree named scanley-2.5.0 in the
current directory. Underneath the new directory, the source code
should be arranged in a layout ready for compilation (if compilation
is needed) and installation. In the top level of new directory tree,
there should be a plain text README file
explaining what the software does and what release this is, and giving
pointers to other resources, such as the project's web site, other
files of interest, etc. Among those other files should be an
INSTALL file, sibling to
the README file, giving instructions on how to build
and install the software for all the operating systems it supports.
As mentioned in
in , there should also
be a COPYING or LICENSE
file, giving the software's terms of distribution.
There should also be a CHANGES file
(sometimes called NEWS), explaining what's new in
this release. The CHANGES file accumulates
changelists for all releases, in reverse chronological order, so that
the list for this release appears at the top of the file. Completing
that list is usually the last thing done on a stabilizing release
branch; some projects write the list piecemeal as they're developing,
others prefer to save it all up for the end and have one person write
it, getting information by combing the version control logs. The list
looks something like this:
Version 2.5.0
(20 December 2004, from /branches/2.5.x)
http://svn.scanley.org/repos/svn/tags/2.5.0/
New features, enhancements:
* Added regular expression queries (issue #53)
* Added support for UTF-8 and UTF-16 documents
* Documentation translated into Polish, Russian, Malagasy
* ...
Bugfixes:
* fixed reindexing bug (issue #945)
* fixed some query bugs (issues #815, #1007, #1008)
* ...
The list can be as long as necessary, but don't bother to
include every little bugfix and feature enhancement. Its purpose is
simply to give users an overview of what they would gain by upgrading
to the new release. In fact, the changelist is customarily included
in the announcement email (see
later in this chapter), so write it with that
audience in mind.
CHANGES Versus ChangeLog
Traditionally, a file named ChangeLog
lists every change ever made to a project—that is, every
revision committed to the version control system. There are
various formats for ChangeLog files; the details of the formats
aren't important here, as they all contain the same information:
the date of the change, its author, and a brief summary (or just
the log message for that change).
A CHANGES file is different. It too is
a list of changes, but only the ones thought important for a
certain audience to see, and often with metadata like the exact
date and author stripped off. To avoid confusion, don't use the
terms interchangeably. Some projects use "NEWS" instead of
"CHANGES"; although this avoids the potential for confusion with
"ChangeLog", it is a bit of a misnomer, since the CHANGES file
retains change information for all releases, and thus has a lot of
old news in addition to the new news at the top.
ChangeLog files may be slowly disappearing anyway. They were
helpful in the days when CVS was the only choice of version control
system, because change data was not easy to extract from CVS.
However, with more recent version control systems, the data that
used to be kept in the ChangeLog can be requested from the version
control repository at any time, making it pointless for the project
to keep a static file containing that data—in fact, worse
than pointless, since the ChangeLog would merely duplicate the log
messages already stored in the repository.
The actual layout of the source code inside the tree should be
the same as, or as similar as possible to, the source code layout one
would get by checking out the project directly from its version
control repository. Usually there are a few differences, for example
because the package contains some generated files needed for
configuration and compilation (see
later in this chapter), or because it includes
third-party software that is not maintained by the project, but that
is required and that users are not likely to already have. But even
if the distributed tree corresponds exactly to some development tree
in the version control repository, the distribution itself should not
be a working copy (see ).
The release is supposed to represent a static reference point—a
particular, unchangeable configuration of source files. If it were a
working copy, the danger would be that the user might update it, and
afterward think that he still has the release when in fact he has
something different.
Remember that the package is the same regardless of the
packaging. The release—that is, the precise entity referred to
when someone says "Scanley 2.5.0"—is the tree created by
unpacking a zip file or tarball. So the project might offer all of
these for download:
scanley-2.5.0.tar.bz2
scanley-2.5.0.tar.gz
scanley-2.5.0.zip
...but the source tree created by unpacking them must be the
same. That source tree is the distribution; the form in which it is
downloaded is merely a matter of convenience. Certain trivial
differences between source packages are allowable: for example, in the
Windows package, text files should have lines ending with CRLF
(Carriage Return and Line Feed), while Unix packages should use just
LF. The trees may be arranged slightly differently between source
packages destined for different operating systems, too, if those
operating systems require different sorts of layouts for compilation.
However, these are all basically trivial transformations. The basic
source files should be the same across all the packagings of a given
release.
To capitalize or not to capitalize
When referring to a project by name, people generally capitalize
it as a proper noun, and capitalize acronyms if there are any:
"MySQL 5.0", "Scanley 2.5.0", etc. Whether this
capitalization is reproduced in the package name is up to the project.
Either Scanley-2.5.0.tar.gz or
scanley-2.5.0.tar.gz would be fine, for example
(I personally prefer the latter, because I don't like to make people
hit the shift key, but plenty of projects ship capitalized packages).
The important thing is that the directory created by unpacking the
tarball use the same capitalization. There should be no surprises:
the user must be able to predict with perfect accuracy the name of the
directory that will be created when she unpacks a distribution.
Pre-releases
When shipping a pre-release or candidate release, the qualifier
is truly a part of the release number, so include it in the name of
the package's name. For example, the ordered sequence of alpha and
beta releases given earlier in
would result in
package names like this:
scanley-2.3.0-alpha1.tar.gz
scanley-2.3.0-alpha2.tar.gz
scanley-2.3.0-beta1.tar.gz
scanley-2.3.0-beta2.tar.gz
scanley-2.3.0-beta3.tar.gz
scanley-2.3.0.tar.gz
The first would unpack into a directory
named scanley-2.3.0-alpha1, the second into
scanley-2.3.0-alpha2, and so on.
Compilation and Installation
For software requiring compilation or installation from source,
there are usually standard procedures that experienced users expect to
be able to follow. For example, for programs written in C, C++, or
certain other compiled languages, the standard under Unix-like systems
is for the user to type:
$ ./configure
$ make
# make install
The first command autodetects as much about the environment as
it can and prepares for the build process, the second command builds
the software in place (but does not install it), and the last command
installs it on the system. The first two commands are done as a
regular user, the third as root. For more details about setting up
this system, see the excellent GNU Autoconf, Automake, and
Libtool book by Vaughan, Elliston, Tromey, and Taylor. It
is published as treeware by New Riders, and its content is also freely
available online at
.
This is not the only standard, though it is one of the most
widespread. The Ant () build
system is gaining popularity, especially with projects written in
Java, and it has its own standard procedures for building and
installing. Also, certain programming languages, such as Perl and
Python, recommend that the same method be used for most programs
written in that language (for example, Perl modules use the
command perl Makefile.PL). If it's not
obvious to you what the applicable standards are for your project, ask
an experienced developer; you can safely assume
that some standard applies, even if you don't
know what it is at first.
Whatever the appropriate standards for you project are, don't
deviate from them unless you absolutely must. Standard installation
procedures are practically spinal reflexes for a lot of system
administrators now. If they see familiar invocations documented in
your project's INSTALL file, that instantly
raises their faith that your project is generally aware of
conventions, and that it is likely to have gotten other things right
as well. Also, as discussed in
in
, having a standard
build procedure pleases potential developers.
On Windows, the standards for building and installing are a bit
less settled. For projects requiring compilation, the general
convention seems to be to ship a tree that can fit into the
workspace/project model of the standard Microsoft development
environments (Developer Studio, Visual Studio, VS.NET, MSVC++, etc.).
Depending on the nature of your software, it may be possible to offer
a Unix-like build option on Windows via the Cygwin
() environment. And of course,
if you're using a language or programming framework that comes with
its own build and install conventions—e.g., Perl or
Python—you should simply use whatever the standard method is for
that framework, whether on Windows, Unix, Mac OS X, or any other
operating system.
Be willing to put in a lot of extra effort in order to make your
project conform to the relevant build or installation standards.
Building and installing is an entry point: it's okay for things to get
harder after that, if they absolutely must, but it would be a shame
for the user's or developer's very first interaction with the software
to require unexpected steps.
Binary Packages
Although the formal release is a source code package, most users
will install from binary packages, either provided by their operating
system's software distribution mechanism, or obtained manually from
the project web site or from some third party. Here "binary" doesn't
necessarily mean "compiled"; it just means any pre-configured form of
the package that allows a user to install it on his computer without
going through the usual source-based build and install procedures. On
RedHat GNU/Linux, it is the RPM system; on Debian GNU/Linux, it is the
APT (.deb) system; on MS Windows, it's usually
.MSI files or self-installing
.exe files.
Whether these binary packages are assembled by people closely
associated with the project, or by distant third parties, users are
going to treat them as equivalent to the
project's official releases, and will file issues in the project's bug
tracker based on the behavior of the binary packages. Therefore, it
is in the project's interest to provide packagers with clear
guidelines, and work closely with them to see to it that what they
produce represents the software fairly and accurately.
The main thing packagers need to know is that they should always
base their binary packages on an official source release. Sometimes
packagers are tempted to pull a later incarnation of the code from the
repository, or include selected changes that were committed after the
release was made, in order to provide users with certain bug fixes or
other improvements. The packager thinks he is doing his users a favor
by giving them the more recent code, but actually this practice can
cause a great deal of confusion. Projects are prepared to receive
reports of bugs found in released versions, and bugs found in recent
trunk and major branch code (that is, found by people who deliberately
run bleeding edge code). When a bug report comes in from these
sources, the responder will often be able to confirm that the bug is
known to be present in that snapshot, and perhaps that it has since
been fixed and that the user should upgrade or wait for the
next release. If it is a previously unknown bug, having the precise
release makes it easier to reproduce and easier to categorize in the
tracker.
Projects are not prepared, however, to receive bug reports based
on unspecified intermediate or hybrid versions. Such bugs can be hard
to reproduce; also, they may be due to unexpected interactions in
isolated changes pulled in from later development, and thereby cause
misbehaviors that the project's developers should not have to take the
blame for. I have even seen dismayingly large amounts of time wasted
because a bug was absent when it should have been
present: someone was running a slightly patched up version, based on
(but not identical to) an official release, and when the predicted bug
did not happen, everyone had to dig around a lot to figure out
why.
Still, there will sometimes be circumstances when a packager
insists that modifications to the source release are necessary.
Packagers should be encouraged to bring this up with the project's
developers and describe their plans. They may get approval, but
failing that, they will at least have notified the project of their
intentions, so the project can watch out for unusual bug reports. The
developers may respond by putting a disclaimer on the project's web
site, and may ask that the packager do the same thing in the
appropriate place, so that users of that binary package know what they
are getting is not exactly the same as what the project officially
released. There need be no animosity in such a situation, though
unfortunately there often is. It's just that packagers have a
slightly different set of goals from developers. The packagers mainly
want the best out-of-the-box experience for their users. The
developers want that too, of course, but they also need to ensure that
they know what versions of the software are out there, so they can
receive coherent bug reports and make compatibility guarantees.
Sometimes these goals conflict. When they do, it's good to keep in
mind that the project has no control over the packagers, and that the
bonds of obligation run both ways. It's true that the project is
doing the packagers a favor simply by producing the software. But the
packagers are also doing the project a favor, by taking on a mostly
unglamorous job in order to make the software more widely available,
often by orders of magnitude. It's fine to disagree with packagers,
but don't flame them; just try to work things out as best you
can.
Testing and Releasing
Once the source tarball is produced from the stabilized release
branch, the public part of the release process begins. But before the
tarball is made available to the world at large, it should be tested
and approved by some minimum number of developers, usually three or
more. Approval is not simply a matter of inspecting the release for
obvious flaws; ideally, the developers download the tarball, build and
install it onto a clean system, run the regression test suite (see
) in
, and do some
manual testing. Assuming it passes these checks, as well as any other
release checklist criteria the project may have, the developers then
digitally sign the tarball using GnuPG
(), PGP
(), or some other program capable
of producing PGP-compatible signatures.
In most projects, the developers just use their personal digital
signatures, instead of a shared project key, and as many developers as
want to may sign (i.e., there is a minimum number, but not a maximum).
The more developers sign, the more testing the release undergoes, and
also the greater the likelihood that a security-conscious user can
find a digital trust path from herself to the tarball.
Once approved, the release (that is, all tarballs, zip files,
and whatever other formats are being distributed) should be placed
into the project's download area, accompanied by the digital
signatures, and by MD5/SHA1 checksums (see ).
There are various standards for doing this. One way is to accompany
each released package with a file giving the corresponding digital
signatures, and another file giving the checksum. For example, if one
of the released packages is scanley-2.5.0.tar.gz,
place in the same directory a file
scanley-2.5.0.tar.gz.asc containing the digital
signature for that tarball, another file
scanley-2.5.0.tar.gz.md5 containing its MD5
checksum, and optionally another,
scanley-2.5.0.tar.gz.sha1, containing the SHA1
checksum. A different way to provide checking is to collect all the
signatures for all the released packages into a single file,
scanley-2.5.0.sigs; the same may be done with the
checksums.
It doesn't really matter which way you do it. Just keep to a
simple scheme, describe it clearly, and be consistent from release to
release. The purpose of all this signing and checksumming is to give
users a way to verify that the copy they receive has not been
maliciously tampered with. Users are about to run this code on their
computers—if the code has been tampered with, an attacker could
suddenly have a back door to all their data. See
later in this chapter for more about paranoia.
Candidate Releases
For important releases containing many changes, many projects
prefer to put out release candidates first,
e.g., scanley-2.5.0-beta1 before
scanley-2.5.0. The purpose of a candidate is to
subject the code to wide testing before blessing it as an official
release. If problems are found, they are fixed on the release branch
and a new candidate release is rolled out
(scanley-2.5.0-beta2). The cycle continues until
no unacceptable bugs are left, at which point the last candidate
release becomes the official release—that is, the only
difference between the last candidate release and the real release
is the removal of the qualifier from the version number.
In most other respects, a candidate release should be treated
the same as a real release. The alpha,
beta, or rc qualifier is
enough to warn conservative users to wait until the real release, and
of course the announcement emails for the candidate releases should
point out that their purpose is to solicit feedback. Other than
that, give candidate releases the same amount of care as regular
releases. After all, you want people to use the candidates, because
exposure is the best way to uncover bugs, and also because you never
know which candidate release will end up becoming the official
release.
Announcing Releases
Announcing a release is like announcing any other event, and
should use the procedures described in
in
. There are a few
specific things to do for releases, though.
Whenever you give the URL to the downloadable release tarball,
make sure to also give the MD5/SHA1 checksums and pointers to the
digital signatures file. Since the announcement happens in multiple
forums (mailing list, news page, etc.), this means users can get the
checksums from multiple sources, which gives the most
security-conscious among them extra assurance that the checksums
themselves have not been tampered with. Giving the link to the
digital signature files multiple times doesn't make those signatures
more secure, but it does reassure people (especially those who don't
follow the project closely) that the project takes security
seriously.
In the announcement email, and on news pages that contain more
than just a blurb about the release, make sure to include the relevant
portion of the CHANGES file, so people can see why it might be in
their interests to upgrade. This is as important with candidate
releases as with final releases; the presence of bugfixes and new
features is important in tempting people to try out a candidate
release.
Finally, don't forget to thank the development team, the
testers, and all the people who took the time to file good bug
reports. Don't single out anyone by name, though, unless there's
someone who is individually responsible for a huge piece of work,
the value of which is widely recognized by everyone in the
project. Just be wary of sliding down the slippery slope of credit
inflation (see
in ).
Maintaining Multiple Release Lines
Most mature projects maintain multiple release lines in
parallel. For example, after 1.0.0 comes out, that line should
continue with micro (bugfix) releases 1.0.1, 1.0.2, etc., until the
project explicitly decides to end the line. Note that merely
releasing 1.1.0 is not sufficient reason to end the 1.0.x line. For
example, some users make it a policy never to upgrade to the first
release in a new minor or major series—they let others shake the
bugs out of, say 1.1.0, and wait until 1.1.1. This isn't necessarily
selfish (remember, they're forgoing the bugfixes and new features
too); it's just that, for whatever reason, they've decided to be very
careful with upgrades. Accordingly, if the project learns of a major
bug in 1.0.3 right before it's about to release 1.1.0, it would be a
bit severe to just put the bugfix in 1.1.0 and tell all the old 1.0.x
users they should upgrade. Why not release both 1.1.0 and 1.0.4, so
everyone can be happy?
After the 1.1.x line is well under way, you can declare 1.0.x to
be at end of life. This should be announced
officially. The announcement could stand alone, or it could be
mentioned as part of a 1.1.x release announcement; however you do
it, users need to know that the old line is being phased out, so they
can make upgrade decisions accordingly.
Some projects set a window of time during which they pledge to
support the previous release line. In an open source context,
"support" means accepting bug reports against that line, and making
maintenance releases when significant bugs are found. Other projects
don't give a definite amount of time, but watch incoming bug reports
to gauge how many people are still using the older line. When the
percentage drops below a certain point, they declare end of life for
the line and stop supporting it.
For each release, make sure to have a target
version or target milestone
available in the bug tracker, so people filing bugs will be able to do
so against the proper release. Don't forget to also have a target
called "development" or "latest" for the most recent development
sources, since some people—not only active developers—will
often stay ahead of the official releases.
Security Releases
Most of the details of handling security bugs were covered in
in
, but there are some
special details to discuss for doing security releases.
A security release is a release made
solely to close a security vulnerability. The code that fixes the bug
cannot be made public until the release is available, which means not
only that the fixes cannot be committed to the repository until the
day of the release, but also that the release cannot be publicly
tested before it goes out the door. Obviously, the developers can
examine the fix among themselves, and test the release privately, but
widespread real-world testing is not possible.
Because of this lack of testing, a security release should
always consist of some existing release plus the fixes for the
security bug, with no other changes. This is
because the more changes you ship without testing, the more likely
that one of them will cause a new bug, perhaps even a new security
bug! This conservatism is also friendly to administrators who may
need to deploy the security fix, but whose upgrade policy prefers that
they not deploy any other changes at the same time.
Making a security release sometimes involves some minor
deception. For example, the project may have been working on a 1.1.3
release, with certain bug fixes to 1.1.2 already publicly declared,
when a security report comes in. Naturally, the developers cannot
talk about the security problem until they make the fix available;
until then, they must continue to talk publicly as though 1.1.3 will
be what it's always been planned to be. But when 1.1.3 actually
comes out, it will differ from 1.1.2 only in the security fixes, and
all those other fixes will have been deferred to 1.1.4 (which, of
course, will now also contain the security
fix, as will all other future releases).
You could add an extra component to an existing release to
indicate that it contains security changes only. For example, people
would be able to tell just from the numbers that 1.1.2.1 is a security
release against 1.1.2, and they would know that any release "higher"
than that (e.g., 1.1.3, 1.2.0, etc.) contains the same security fixes.
For those in the know, this system conveys a lot of information. On
the other hand, for those not following the project closely, it can be
a bit confusing to see a three-component release number most of the
time with an occasional four-component one thrown in seemingly at
random. Most projects I've looked at choose consistency and simply
use the next regularly scheduled number for security releases, even
when it means shifting other planned releases by one.
Releases and Daily Development
Maintaining parallel releases simultaneously has implications
for how daily development is done. In particular, it makes
practically mandatory a discipline that would be recommended anyway:
have each commit be a single logical change, and never mix unrelated
changes in the same commit. If a change is too big or too disruptive
to do in one commit, break it across N commits, where each commit is a
well-partitioned subset of the overall change, and includes nothing
unrelated to the overall change.
Here's an example of an ill-thought-out commit:
------------------------------------------------------------------------
r6228 | jrandom | 2004-06-30 22:13:07 -0500 (Wed, 30 Jun 2004) | 8 lines
Fix Issue #1729: Make indexing gracefully warn the user when a file
is changing as it is being indexed.
* ui/repl.py
(ChangingFile): New exception class.
(DoIndex): Handle new exception.
* indexer/index.py
(FollowStream): Raise new exception if file changes during indexing.
(BuildDir): Unrelatedly, remove some obsolete comments, reformat
some code, and fix the error check when creating a directory.
Other unrelated cleanups:
* www/index.html: Fix some typos, set next release date.
------------------------------------------------------------------------
The problem with it becomes apparent as soon as someone needs to
port the BuildDir error check fix over to a
branch for an upcoming maintenance release. The porter doesn't want
any of the other changes—for example, perhaps the fix to issue
#1729 wasn't approved for the maintenance branch at all, and the
index.html tweaks would simply be irrelevant
there. But she cannot easily grab just the
BuildDir change via the version control tool's
merge functionality, because the version control system was told that
that change is logically grouped with all these other unrelated
things. In fact, the problem would become apparent even before the
merge. Merely listing the change for voting would become problematic:
instead of just giving the revision number, the proposer would have to
make a special patch or change branch just to isolate the portion of
the commit being proposed. That would be a lot of work for others to
suffer through, and all because the original committer couldn't be
bothered to break things into logical groups.
In fact, that commit really should have been
four separate commits: one to fix issue
#1729, another to remove obsolete comments and reformat code in
BuildDir, another to fix the error check in
BuildDir, and finally, one to tweak
index.html. The third of those commits would be
the one proposed for the maintenance release branch.
Of course, release stabilization is not the only reason why
having each commit be one logical change is desirable.
Psychologically, a semantically unified commit is easier to review,
and easier to revert if necessary (in some version control systems,
reversion is really a special kind of merge anyway). A little
up-front discipline on everyone's part can save the project a lot of
headache later.
Planning Releases
One area where open source projects have historically differed
from proprietary projects is in release planning. Proprietary
projects usually have firmer deadlines. Sometimes it's because
customers were promised that an upgrade would be available by a
certain date, because the new release needs to be coordinated with
some other effort for marketing purposes, or because the venture
capitalists who invested in the whole thing need to see some results
before they put in any more funding. Free software projects, on the
other hand, were until recently mostly motivated by amateurism in the
most literal sense: they were written for the love of it. No one felt
the need to ship before all the features were ready, and why should
they? It wasn't as if anyone's job was on the line.
Nowadays, many open source projects are funded by corporations,
and are correspondingly more and more influenced by deadline-conscious
corporate culture. This is in many ways a good thing, but it can
cause conflicts between the priorities of those developers who are
being paid and those who are volunteering their time. These conflicts
often happen around the issue of when and how to schedule releases.
The salaried developers who are under pressure will naturally want to
just pick a date when the releases will occur, and have everyone's
activities fall into line. But the volunteers may have other
agendas—perhaps features they want to complete, or some testing
they want to have done—that they feel the release should wait
on.
There is no general solution to this problem except discussion
and compromise, of course. But you can minimize the frequency and
degree of friction caused, by decoupling the proposed
existence of a given release from the date when
it would go out the door. That is, try to steer discussion toward the
subject of which releases the project will be making in the near- to
medium-term future, and what features will be in them, without at
first mentioning anything about dates, except for rough guesses with
wide margins of error. By nailing down feature sets early, you reduce
the complexity of the discussion centered on any individual release,
and therefore improve predictability. This also creates a kind of
inertial bias against anyone who proposes to expand the definition of
a release by adding new features or other complications. If the
release's contents are fairly well defined, the onus is on the
proposer to justify the expansion, even though the date of the release
may not have been set yet.
In his multi-volume biography of Thomas Jefferson,
Jefferson and His Time, Dumas Malone tells the
story of how Jefferson handled the first meeting held to decide the
organization of the future University of Virginia. The University had
been Jefferson's idea in the first place, but (as is the case
everywhere, not just in open source projects) many other parties had
climbed on board quickly, each with their own interests and agendas.
When they gathered at that first meeting to hash things out, Jefferson
made sure to show up with meticulously prepared architectural
drawings, detailed budgets for construction and operation, a proposed
curriculum, and the names of specific faculty he wanted to import from
Europe. No one else in the room was even remotely as prepared; the
group essentially had to capitulate to Jefferson's vision, and the
University was eventually founded more or less in accordance with his
plans. The facts that construction went far over budget, and that
many of his ideas did not, for various reasons, work out in the end,
were all things Jefferson probably knew perfectly well would happen.
His purpose was strategic: to show up at the meeting with something so
substantive that everyone else would have to fall into the role of
simply proposing modifications to it, so that the overall shape, and
therefore schedule, of the project would be roughly as he
wanted.
In the case of a free software project, there is no single
"meeting", but instead a series of small proposals made mostly by
means of the issue tracker. But if you have some credibility in the
project to start with, and you start assigning various features,
enhancements, and bugs to target releases in the issue tracker,
according to some announced overall plan, people will mostly go along
with you. Once you've got things laid out more or less as you want
them, the conversations about actual release
dates will go much more smoothly.
It is crucial, of course, to never present any individual
decision as written in stone. In the comments associated with each
assignment of an issue to a specific future release, invite
discussion, dissent, and be genuinely willing to be persuaded whenever
possible. Never exercise control merely for the sake of exercising
control: the more deeply others participate in the release planning
process (see
in
), the easier it
will be to persuade them to share your priorities on the issues that
really count for you.
The other way the project can lower tensions around release
planning is to make releases fairly often. When there's a long time
between releases, the importance of any individual release is
magnified in everyone's minds; people are that much more crushed when
their code doesn't make it in, because they know how long it might be
until the next chance. Depending on the complexity of the release
process and the nature of your project, somewhere between every three
and six months is usually about the right gap between releases, though
maintenance lines may put out micro releases a bit faster, if there is
demand for them.