Improve Multi-threaded Performance. #450
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The idea of this pull request is to improve the performance of CPM in multi-threaded conditions by removing the
cpm_add_subdirectory()calls from the scope of the lock.Before this change, each instance of CMake must wait for each instance that gets hold of the lock before it to completely finish checking if the cache is clean, then adding the subdirectory. This can become a very long process for even moderately sized libraries.
To solve this problem, I propose moving the
file(LOCK ... RELEASE)command to just after the fetch has taken place, and adding another one right before checking if the cache is clean. This will allow the first process to stop all others during the download, then when it is unlocked, all processes can simultaneously check the cache (still only done by processes that did not perform the download) and add the new subdirectory.This will help alleviate, but will not fix #419.