[platform-debug-dev] Launching with background build

[John Arthorne <John_Arthorne@xxxxxxxxxx>]

Hello,

I am planning on soon releasing new
platform support for background autobuild.  I have been self-hosting
on this for a few weeks, and one area that doesn't run very smoothly is
launching.  Here is one scenario:

- Autobuild is on, background build
enabled.
- User starts a background CVS checkout
operation.  Say it's a slow connection and it takes a few minutes.
- While waiting, the user continues
to do some work, modifying and saving a java file
- The save operation completes because
it is orthogonal to the checkout (operating on disjoint set of resources)
- The subsequent build cannot proceed,
because building requires write access to all projects
- The user then launches a debug VM
that involves the changed class
- Since the build has not run, the launched
VM will operate on stale .class files

One possible solution is to wait for
the auto-build to complete before launching.  This can be accomplished
using the job manager's join method, which allows a thread to join a running
job:

Platform.getJobManager().join(ResourcesPlugin.FAMILY_AUTO_BUILD,
null);

The problem is, this will now block
the launch from proceeding, possibly for several minutes until the checkout
completes.  A fancier solution would be to detect that the auto-build
is blocked, and then give the user the option to proceed anyway.  You
can determine that a job is blocked by seeing if it is in the waiting state
(this is pseudo-code, I haven't test it):

Job[] build = Platform.getJobManager().find(ResourcesPlugin.FAMILY_AUTO_BUILD);
if (build.length == 1) {
   if (build[0].getState()
== Job.WAITING) {
       //auto-build
is blocked by another process, so ask the user if they want to launch or
wait
   } else if (build[0].getState()
== Job.RUNNING) {
       //auto-build
is running, so join it to wait until it completes
      build[0].join();
   }
}

That way the user can choose to launch
without building.  If they know they have not made any changes that
will affect the running program, they will want to proceed without waiting.

Let me know your thoughts on this.

More info on the platform changes can
be found here (doc timelines are outdated):

http://dev.eclipse.org/viewcvs/index.cgi/%7Echeckout%7E/platform-core-home/documents/plan_concurrency_listeners.html

Background build can currently be enabled
with the following debug .options:

org.eclipse.core.resources/debug=true
org.eclipse.core.resources/build/background="">

(background build is broken in I20030916,
but should be fixed for tomorrow)

John.