Introduce libcxx <shared_mutex>

git@github.com:llvm-mirror/libcxx.git
78d6a7767ed57b50122a161b91f59f19c9bd0d19

third_party/libcxx/shared_mutex.cc

@@ -0,0 +1,119 @@
+// clang-format off
+//===---------------------- shared_mutex.cpp ------------------------------===//
+//
+// 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 "third_party/libcxx/__config"
+#ifndef _LIBCPP_HAS_NO_THREADS
+
+#include "third_party/libcxx/shared_mutex"
+#if defined(__unix__) && !defined(__ANDROID__) && defined(__ELF__) && defined(_LIBCPP_HAS_COMMENT_LIB_PRAGMA)
+#pragma comment(lib, "pthread")
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// Shared Mutex Base
+__shared_mutex_base::__shared_mutex_base()
+    : __state_(0)
+{
+}
+
+// Exclusive ownership
+
+void
+__shared_mutex_base::lock()
+{
+    unique_lock<mutex> lk(__mut_);
+    while (__state_ & __write_entered_)
+        __gate1_.wait(lk);
+    __state_ |= __write_entered_;
+    while (__state_ & __n_readers_)
+        __gate2_.wait(lk);
+}
+
+bool
+__shared_mutex_base::try_lock()
+{
+    unique_lock<mutex> lk(__mut_);
+    if (__state_ == 0)
+    {
+        __state_ = __write_entered_;
+        return true;
+    }
+    return false;
+}
+
+void
+__shared_mutex_base::unlock()
+{
+    lock_guard<mutex> _(__mut_);
+    __state_ = 0;
+    __gate1_.notify_all();
+}
+
+// Shared ownership
+
+void
+__shared_mutex_base::lock_shared()
+{
+    unique_lock<mutex> lk(__mut_);
+    while ((__state_ & __write_entered_) || (__state_ & __n_readers_) == __n_readers_)
+        __gate1_.wait(lk);
+    unsigned num_readers = (__state_ & __n_readers_) + 1;
+    __state_ &= ~__n_readers_;
+    __state_ |= num_readers;
+}
+
+bool
+__shared_mutex_base::try_lock_shared()
+{
+    unique_lock<mutex> lk(__mut_);
+    unsigned num_readers = __state_ & __n_readers_;
+    if (!(__state_ & __write_entered_) && num_readers != __n_readers_)
+    {
+        ++num_readers;
+        __state_ &= ~__n_readers_;
+        __state_ |= num_readers;
+        return true;
+    }
+    return false;
+}
+
+void
+__shared_mutex_base::unlock_shared()
+{
+    lock_guard<mutex> _(__mut_);
+    unsigned num_readers = (__state_ & __n_readers_) - 1;
+    __state_ &= ~__n_readers_;
+    __state_ |= num_readers;
+    if (__state_ & __write_entered_)
+    {
+        if (num_readers == 0)
+            __gate2_.notify_one();
+    }
+    else
+    {
+        if (num_readers == __n_readers_ - 1)
+            __gate1_.notify_one();
+    }
+}
+
+
+// Shared Timed Mutex
+// These routines are here for ABI stability
+shared_timed_mutex::shared_timed_mutex() : __base() {}
+void shared_timed_mutex::lock()     { return __base.lock(); }
+bool shared_timed_mutex::try_lock() { return __base.try_lock(); }
+void shared_timed_mutex::unlock()   { return __base.unlock(); }
+void shared_timed_mutex::lock_shared() { return __base.lock_shared(); }
+bool shared_timed_mutex::try_lock_shared() { return __base.try_lock_shared(); }
+void shared_timed_mutex::unlock_shared() { return __base.unlock_shared(); }
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !_LIBCPP_HAS_NO_THREADS