[PATCH] D60758: Add an assertion that parallelForEach doesn't nest.

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added inline comments.


================
Comment at: lld/Common/Threads.cpp:13
 bool lld::ThreadsEnabled = true;
+thread_local bool lld::ParallelForEachRunning;
----------------
This doesn't have to be `thread_local`. This is a fundamental problem of `TaskGroup`.

```
template <class IterTy, class FuncTy>
void parallel_for_each(IterTy Begin, IterTy End, FuncTy Fn) {
  TaskGroup TG;
.... // In ~Latch called by ~TaskGroup, all threads of the default executor can block on different `std::mutex`es if there are multiple concurrent `parallel_for_each` invocations.
}
```

It doesn't need nested `parallel_for_each` to get stuck. It just needs more concurrent `parallel_for_each` invocations than the number of executors.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D60758/new/

https://reviews.llvm.org/D60758