I have not looked at parallel execution closely and don't fully
understand the usecase, but I am not sure race condition is the code in
DefaultClassRealmManager.
As far as I can tell, DefaultClassRealmManager only provides create*
methods, which create new realms and the current implementation looks
proper.
If parallel execution logic needs to be able to create-or-query plugin
realms in thread-safe manner, I think this should be implemented
somewhere at higher levels, where one-plugin-realm-per-plugin-perproject
constraint can be enforced properly.
Again, I do not know parallel execution, so I can be completely wrong
about this.
--
Regards,
Igor
On 12-07-26 12:36 PM, Jason van Zyl wrote:
In that case we may just want to differentiate because the parallel execution
use case is not one that happens inside the IDE. In the case of CLI execution
it can all be handled up front as additional realm construction beyond the CLI
execution isn't going to happen. In an IDE or shell wouldn't a map of realms
keyed by GAV suffice? Sync on write everyone is free to read?
On Jul 26, 2012, at 12:06 PM, Igor Fedorenko wrote:
This is required in m2e where multiple versions of the same plugin can
coexist for long time in the same container.
--
Regards,
Igor
On 12-07-26 8:44 AM, Kristian Rosenvold wrote:
There is a race condition in parallel builds that occurs related to
this piece of code:
http://maven.apache.org/ref/3.0.4/maven-core/xref/org/apache/maven/classrealm/DefaultClassRealmManager.html#75
The thing is, for some reason, there's a loop that retries the class
realm generation with a random suffix if the class realm already
exists. In a parallel run, there will be multiple threads requesting
the same realm-id, which semantically should map to the same instance
of the class realm.
(Most plugins do not really mind if there's a duplicate class realm
every now and then, but some take it very seriously ;)
I'm tempted to change the semantics of the "newRealm" method to
"getOrCreateRealm", since that seems to be the correct semantics no
matter what. I've tried tracking the origin of the while loop, and it
seems to be very old. Anyone have any idea of what purpose it served ?
Kristian
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Thanks,
Jason
----------------------------------------------------------
Jason van Zyl
Founder & CTO, Sonatype
Founder, Apache Maven
http://twitter.com/jvanzyl
---------------------------------------------------------
The modern conservative is engaged in one of man's oldest exercises in moral
philosophy; that is,
the search for a superior moral justification for selfishness.
-- John Kenneth Galbraith
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