[libc-commits] [libc] [libc] Implement barriers for pthreads (PR #148948)

[Brooks Moses via libc-commits]

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@@ -0,0 +1,83 @@
+//===-- Implementation of Barrier class ------------- ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/threads/barrier.h"
+#include "barrier.h"
+#include "hdr/errno_macros.h"
+#include "src/__support/threads/mutex.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+const int BARRIER_FIRST_EXITED = -1;
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brooksmoses wrote:

(Repeating offline conversation, for the record.)

I think the concept of one thread returning a special value is fairly pthreads-specific.  C11 `threads.h` doesn't have a barrier functionality, and C++20's `std::barrier` doesn't return a value.  And if this does end up needing to be used by a different threading API, it might be a different return value like returning the decremented thread count.  So I would personally use the pthreads constant for it, until we find another thing that needs this return value.

For the second point -- you need to declare the variable as `static` to keep it from getting global linkage.  With global linkage, it's no longer a compile-time constant since some other compilation unit could access it and change it.



https://github.com/llvm/llvm-project/pull/148948