mirror of https://github.com/sbt/sbt.git
5dc671c7f8
Construction of Scala providers was already properly synchronized jvm and machine-wide. The cache on top of construction was not and neither was the newer ClassLoaderCache. This could cause the same Scala version to be loaded in multiple class loaders, taking up more permgen space and possibly decreasing performance due to less effective jit. The issue is very rare in practice for 0.13 because of the low probability of contention on ClassLoaderCache. This is because the work for a cache miss is mainly the construction of a URLClassLoader. In 0.12, however, the work potentially involved network access and class loading (not just class loader construction), thus greatly increasing the probability of contention and thus duplicate work (i.e. class loader construction). When there is contention, multiple class loaders are constructed and then preserved by the scalaInstance task in each project throughout the first task execution. Only when multiple scalaInstance tasks execute simultaneously and only during the first execution does this occur. (Technically, it could still happen later, but it doesn't in practice.) This means that the number of duplicate class loaders should quickly saturate instead of growing linearly with the number of projects. It also means that the impact depends on the exact tree structure of projects. A linear chain of dependencies will be unaffected, but a build with independent leaves may be limited by the number of cores. The number of cores affects the number of threads typically used by the task engine, which limits the number of concurrently executing scalaInstance tasks. In summary, this might affect the first, cold compilation of a multi-module project with independent leaves on a multi-core machine with Scala version different from the version used for sbt. It might increase the maximum permgen requirements as well as slow the jit compilation by up to one task execution. Subsequent compilations should be unaffected and the permgen utilization return to be as expected. |
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| .. | ||
| Docs.scala | ||
| Proguard.scala | ||
| Release.scala | ||
| Sbt.scala | ||
| Status.scala | ||
| Sxr.scala | ||
| Transform.scala | ||
| Util.scala | ||
| build.properties | ||
| p.sbt | ||