Synchronize the access to LRUCache

[ramele1907]

• a wizard that is creating multiple cdt projects encounters ConcurrentModificationException

[jonahgraham]

Hi @ramele1907 - thanks for the PR. Unfortunately the code as provided doesn't compile. See build ouput for more details.

findPathInProjectCache has some more complicated semantics as it is a map of maps, so the inner map probably needs synchronizing too. e.g. add additional Collections.synchronizedMap around the new LRUCache in findPathInProject.

Because # of reads far outweigh number of writes and you indicated that multiple projects are being created simultaneously, did you consider concurrency instead of synchronizing all accesses to the map? Those caches were added in 9e7b5be to dramatically speed up the code, and I think that adding synchronized around each read access may have an unintentional slowdown. If you can demonstrate that synchronizedMap doesn't (seriously) negatively affect performance (see the lined commit for some stats) then we don't need to consider concurrency.

It would help if there is a way to reproduce the problem so that we can see the problem in action.