[libc-commits] [libc] [libc] add rwlock (PR #94156)

[Michael Jones via libc-commits]

================
@@ -0,0 +1,525 @@
+//===--- Implementation of a Linux RwLock class ---------------*- 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_LINUX_RWLOCK_H
+#define LLVM_LIBC_SRC_SUPPORT_THREADS_LINUX_RWLOCK_H
+
+#include "hdr/errno_macros.h"
+#include "hdr/types/pid_t.h"
+#include "src/__support/CPP/atomic.h"
+#include "src/__support/CPP/optional.h"
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_assert.h"
+#include "src/__support/macros/attributes.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/threads/linux/futex_utils.h"
+#include "src/__support/threads/linux/futex_word.h"
+#include "src/__support/threads/linux/raw_mutex.h"
+#include "src/__support/threads/sleep.h"
+
+#ifndef LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT
+#define LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT 100
+#endif
+
+#ifndef LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY
+#define LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY 1
+#warning "LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY is not defined, defaulting to 1"
+#endif
+
+#if LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY
+#include "src/__support/time/linux/monotonicity.h"
+#endif
+
+namespace LIBC_NAMESPACE {
+class RwLock {
+public:
+  enum class Role : char { Reader, Writer };
----------------
michaelrj-google wrote:

if the intent is just to use a small storage type for `Role` then I'd recommend using `uint8_t` instead of `char`.

https://github.com/llvm/llvm-project/pull/94156