[libc-commits] [libc] [libc] Add Darwin mutex support via os_sync primitives (PR #167722)

[Schrodinger ZHU Yifan via libc-commits]

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@@ -0,0 +1,78 @@
+//===--- Futex utils for Darwin ------------------------*- C++-*-===//
+//
+// 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
+//
+//===------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_THREADS_DARWIN_FUTEX_UTILS_H
+#define LLVM_LIBC_SRC___SUPPORT_THREADS_DARWIN_FUTEX_UTILS_H
+
+#include "src/__support/CPP/atomic.h"
+#include "src/__support/CPP/optional.h"
+#include "src/__support/time/abs_timeout.h"
+#include "src/__support/time/clock_conversion.h"
+
+#include <os/os_sync_wait_on_address.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+using FutexWordType = uint32_t;
+
+struct Futex : public cpp::Atomic<FutexWordType> {
+  using cpp::Atomic<FutexWordType>::Atomic;
+  using Timeout = internal::AbsTimeout;
+
+  LIBC_INLINE long wait(FutexWordType val, cpp::optional<Timeout> timeout,
+                        bool /* is_shared */) {
+    // TODO(bojle): consider using OS_SYNC_WAIT_ON_ADDRESS_SHARED to sync
+    // betweeen processes. Catch: it is recommended to only be used by shared
+    // processes, not threads of a same process.
+
+    for (;;) {
+      if (this->load(cpp::MemoryOrder::RELAXED) != val)
+        return 0;
+      long ret = 0;
+      if (timeout) {
+        // Assuming, OS_CLOCK_MACH_ABSOLUTE_TIME is equivalent to CLOCK_REALTIME
+        uint64_t tnsec = timeout->get_timespec().tv_sec * 1000000000 +
+                         timeout->get_timespec().tv_nsec;
+        ret = os_sync_wait_on_address_with_timeout(
+            reinterpret_cast<void *>(this), static_cast<uint64_t>(val),
+            sizeof(FutexWordType), OS_SYNC_WAIT_ON_ADDRESS_NONE,
+            OS_CLOCK_MACH_ABSOLUTE_TIME, tnsec);
+      } else {
+        ret = os_sync_wait_on_address(
+            reinterpret_cast<void *>(this), static_cast<uint64_t>(val),
+            sizeof(FutexWordType), OS_SYNC_WAIT_ON_ADDRESS_NONE);
+      }
+      if ((ret < 0) && (errno == ETIMEDOUT)) {
+        return -ETIMEDOUT;
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SchrodingerZhu wrote:

Please remove extra brace to conform LLVM's guide line.

https://github.com/llvm/llvm-project/pull/167722