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Active Development Warning: The features described in this chapter
are likely to change in incompatible ways before the 1
.0 release of
arch
.
In some circumstances, it is very useful to trigger actions upon the detection of changes to an archive. For example, you might want to send an email notification whenever new revisions are checked in.
The command notify
provides this capability:
% larch notify NOTIFICATION-DIR
That command reads configuration files found in NOTIFICATION-DIR
.
Those configuration files explain what parts of which repositories to
monitor, and what actions to take upon changes. When changes are
detected, notify
invokes actions.
This chapter explains notify
in general. It documents the format of
a NOTIFICATION-DIR
and the configuration files. It explains what
notify
does.
|=rules.archives| |=rules.categories| |=rules.branches| |=rules.versions|
notify
is controlled by four configuration files, found at the root
of a NOTIFICATION-DIR
. These are:
=rules.archives Specifies actions to take whenever new categories are added to specific archives. =rules.categories Specifies actions to take whenever new branches are added to specific categories. =rules.branches Specifies actions to take whenever new versions are added to specific branches. =rules.versions Specifies actions to take whenever new revisions are added to specific versions.
Within these files, blank lines are permitted and comments begin with '#' and continue to the end of line.
The file =rules.versions
contains lines with the format:
VERSION ACTION
where VERSION
is a fully-qualified version name, and action a string
(with no whitespace) of the form:
COMMAND:THUNK
Whenever new revisions are detected in VERSION
, notify
invokes:
larch COMMAND THUNK RVN ...
where COMMAND
and THUNK
are from the configuration file, and the
trailing RVN
arguments are a list of fully qualified revision names
of newly detected revisions.
The file =rules.branches
is similar. It contains lines of the form:
BRANCH COMMAND:THUNK VERSION-ACTION
Whenever new versions are created in BRANCH
, notify
takes two
actions. First, it invokes:
larch COMMAND THUNK VSN ...
Second, it adds new rules to =rules.versions
of the form:
VSN VERSION-ACTION
The files =rules.categories
and =rules.archives
are similar. The
former contains lines of the form:
CATEGORY COMMAND:THUNK BRANCH-ACTION VERSION-ACTION
and the latter lines of the form:
ARCHIVE COMMAND:THUNK CATEGORY-ACT BRANCH-ACT VERSION-ACT
In addition to the configuration files, notify
maintains its private
state in NOTIFY-DIR
. In particular, it keeps track of what
notifications have already been sent, in order to try to avoid sending
redundant notifications.
Configuring notifiers for every category, branch, and version in an
archive is quite simple: you only need to write the =rules.archives
file -- other configuration files will be automatically generated from
that.
The initial =rules.archives
file should contain lines of the form:
ARCHIVE COMMAND:THUNK CATEGORY-ACT BRANCH-ACT VERSION-ACT
for each set of actions you want to trigger. After creating the config
file, run notify
in that directory. The first run will detect all
categories in the repository, invoke COMMAND
for those, and create a
rules.categories
file with lines:
CATEGORY CATEGORY-ACT BRANCH-ACT VERSION-ACT
Then notify
will read that config file, detect all the branches in
the repository, invoke CATEGORY-ACT
, and create =rules.branches
.
Finally, =rules.versions
will be automatically created in a similar
way.
Whenever a new category, branch, or version is added to an archive,
the rules files will be automatically updated to reflect the addition
(when notify
is run, of course).
These commands can be used in notifier rules to send mail announcing new additions to an archive:
mail-new-categories mail-new-branches mail-new-versions mail-new-revisions
This command, if invoked for new revisions, can be used to add those
revisions to the revision library registered with
my-revision-library
:
notify-library
Finally, the noop
command can be used as a place-holder for notifier
events where no actions is needed.
Putting those commands together, you can create an =rules.archives
file that sends out announcements and updates a revision library for
an archive (long lines wrapped for legibility):
/*insert
lord@emf.net--2003 mail-new-categories:lord \ mail-new-branches:lord \ mail-new-versions:lord \ mail-new-revisions:lord
lord@emf.net--2003 noop:notify-library:lord \ noop:notify-library:lord \ noop:notify-library:lord \ notify-library:lord
/*end-insert
Unfortunately, some fundamental physical properties of the universe
make it impossible for notify
to guarantee that actions will be
invoked only once for each new category, branch, version, or revision.
A (presumably rare) well timed interrupt or system failure can cause
notify
to invoke actions more than once for a given change to the
archive.
Consequently, actions should be designed to be robust against that eventuality.
notify
is designed to be safe in the face of concurrent invocations:
if two processes invoke notify
at the same time, everything should
work wonderfully with no resultant redundant actions or NOTIFY-DIR
corruptions.
One strategy for using notify
is to run it from a cron
job.
These commands (and only these commands) modify arch repositories in
ways that are significant to notify
:
make-category make-branch make-version import commit tag
If you register a notifier directory with the command my-notifier
:
% larch my-notifier NOTIFIER-DIR
then the commands listed above will, after completing their work,
spawn a detached daemon process that runs larch notify
in that
directory. Note that the start times and exit status of those daemons
are recorded in ~/.arch-params/log-file
which can be useful when
trying to debug problems. You may want to clear that file from
time-to-time.
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