llvm /
llvm /
8e834b5cde54810be54679924dcd11ec662eba2f Parallel: only allow the first TaskGroup to run tasks parallelly
Summary:
Concurrent (e.g. nested) llvm::parallel::for_each() may lead to dead
locks. See PR35788 (fixed by rLLD322041) and PR41508 (fixed by D60757).
When parallel_for_each() is about to return, in ~Latch() called by
~TaskGroup(), a thread (in the default executor) may block in
Latch::sync() waiting for Count to become zero. If all threads in the
default executor are blocked, it is a dead lock.
To fix this, force serial execution if the current TaskGroup is not the
first one. For a nested llvm::parallel::for_each(), this parallelizes
the outermost loop and serializes inner loops.
Differential Revision: https://reviews.llvm.org/D61115
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@359182 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed
