[libc-commits] [libc] [libc][Semaphore] Add public sem_t type and entry (PR #213489)

[Pengxiang Huang via libc-commits]

================
@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Definition of the sem_t type.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TYPES_SEM_T_H
+#define LLVM_LIBC_TYPES_SEM_T_H
+
+#include "__futex_word.h"
+
+typedef struct {
+  // The semaphore count. Waiters block on this word.
+  __futex_word __value;
+  // Set to a fixed value by sem_init/sem_open and cleared by sem_destroy, so
+  // that operations on an uninitialized or destroyed semaphore can be detected.
+  unsigned int __canary;
+  // Whether the semaphore is shared between processes.
+  unsigned int __is_shared : 1;
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Pengxiang-Huang wrote:

The `sem_t` is a public class in the user space, and double underscore prefix make them reserved and avoid collision. 

https://github.com/llvm/llvm-project/pull/213489