My multi-module POM contains of ten modules. Each of that modules does the same: Invoke the 'copy' goal of the dependency plugin. The idea is to have ten copies of the identical source, which then will end up in ten different targets by getting furthere processed.
As long as I do not use more than one Maven worker thread, everything works well always. But when using -T 5 to have five worker threads, rather often the reactor fails because the source file is locked:
So it seems that the 'copy' task actually is locking the source file, which is not multi-threading-compatible. Hence, either that is a bug and should get fixed, or it is on purpose, then this goal has to be marked as non-multithreading-able.