Relax synchronization in Mojos

[jhonnen]

https://bugs.eclipse.org/bugs/show_bug.cgi?id=571434
https://bugzillaattachments.eclipsecontent.org/bugs/attachment.cgi?id=285635

Currently most (all?) tycho Mojos synchronize on a static lock, effectively allowing only different goals to run in parallel.
Especially the (relatively) long-running compile and package mojos spend more time waiting for the lock than doing actual work in a build with 32 threads.

Maven only recommends that pessimistic lock pattern "if a mojo uses a known-non-threadsafe external dependency" [1].
AFAICS that's not the case. Removing the locks speeds up a mvn clean package -T 2C (=32) a lot: 18min vs 1h before.
See the attached comparison.

[1] https://cwiki.apache.org/confluence/display/MAVEN/Parallel+builds+in+Maven+3

[mickaelistria]

Thanks for the patch.
Do you want to keep this issue open to track further improvements or do you prefer that we close it?

[jhonnen]

Those two mojos were just the low hanging fruits. I'll try to check the other mojos next week.

[jhonnen]

Apart from those two mojos, only the P2MetadataMojo blocks for some significant (but much less) time in our build. But there's a lot going on and I can't quite guarantee its threadsafety.
I don't have the time to dig deeper ATM, so I'll close this issue for now.