[all-commits] [llvm/llvm-project] 87ca22: [Support] Attempt to fix deadlock in ThreadGroup

[Tom Stellard via All-commits]

  Branch: refs/heads/release/13.x
  Home:   https://github.com/llvm/llvm-project
  Commit: 87ca22cba2fad9bbf553a74eced3b7bb69e187be
      https://github.com/llvm/llvm-project/commit/87ca22cba2fad9bbf553a74eced3b7bb69e187be
  Author: Alexandre Ganea <alexandre.ganea at ubisoft.com>
  Date:   2021-12-16 (Thu, 16 Dec 2021)

  Changed paths:
    M llvm/include/llvm/Support/Parallel.h
    M llvm/lib/Support/Parallel.cpp

  Log Message:
  -----------
  [Support] Attempt to fix deadlock in ThreadGroup

This is an attempt to fix the situation described by https://reviews.llvm.org/D104207#2826290 and PR41508.
See sequence of operations leading to the bug in https://reviews.llvm.org/D104207#3004689

We ensure that the Latch is completely "free" before decrementing the number of TaskGroupInstances.

Differential revision: https://reviews.llvm.org/D109914

(cherry picked from commit 7b25fa8c7a151e94be46ed8f0a56bf4e2af1c104)