Each Buildmaster has a set of Scheduler objects, each of which
gets a copy of every incoming Change. The Schedulers are responsible
for deciding when Builds should be run. Some Buildbot installations
might have a single Scheduler, while others may have several, each for
a different purpose.
For example, a “quick” scheduler might exist to give immediate
feedback to developers, hoping to catch obvious problems in the code
that can be detected quickly. These typically do not run the full test
suite, nor do they run on a wide variety of platforms. They also
usually do a VC update rather than performing a brand-new checkout
each time. You could have a “quick” scheduler which used a 30 second
timeout, and feeds a single “quick” Builder that uses a VC
mode='update' setting.
A separate “full” scheduler would run more comprehensive tests a
little while later, to catch more subtle problems. This scheduler
would have a longer tree-stable-timer, maybe 30 minutes, and would
feed multiple Builders (with a mode= of 'copy',
'clobber', or 'export').
The tree-stable-timer and fileIsImportant decisions are
made by the Scheduler. Dependencies are also implemented here.
Periodic builds (those which are run every N seconds rather than after
new Changes arrive) are triggered by a special Periodic
Scheduler subclass. The default Scheduler class can also be told to
watch for specific branches, ignoring Changes on other branches. This
may be useful if you have a trunk and a few release branches which
should be tracked, but when you don't want to have the Buildbot pay
attention to several dozen private user branches.
When the setup has multiple sources of Changes the category
can be used for Scheduler objects to filter out a subset
of the Changes. Note that not all change sources can attach a category.
Some Schedulers may trigger builds for other reasons, other than recent Changes. For example, a Scheduler subclass could connect to a remote buildmaster and watch for builds of a library to succeed before triggering a local build that uses that library.
Each Scheduler creates and submits BuildSet objects to the
BuildMaster, which is then responsible for making sure the
individual BuildRequests are delivered to the target
Builders.
Scheduler instances are activated by placing them in the
c['schedulers'] list in the buildmaster config file. Each
Scheduler has a unique name.