N3659: Shared locking in C++ Revision 2, c++1y only
llvm-svn: 191127
diff --git a/libcxx/src/shared_mutex.cpp b/libcxx/src/shared_mutex.cpp
new file mode 100644
index 0000000..5fb22e4
--- /dev/null
+++ b/libcxx/src/shared_mutex.cpp
@@ -0,0 +1,101 @@
+//===---------------------- shared_mutex.cpp ------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#define _LIBCPP_BUILDING_SHARED_MUTEX
+#include "shared_mutex"
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+shared_mutex::shared_mutex()
+ : __state_(0)
+{
+}
+
+// Exclusive ownership
+
+void
+shared_mutex::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::try_lock()
+{
+ unique_lock<mutex> lk(__mut_);
+ if (__state_ == 0)
+ {
+ __state_ = __write_entered_;
+ return true;
+ }
+ return false;
+}
+
+void
+shared_mutex::unlock()
+{
+ lock_guard<mutex> _(__mut_);
+ __state_ = 0;
+ __gate1_.notify_all();
+}
+
+// Shared ownership
+
+void
+shared_mutex::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::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::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();
+ }
+}
+
+
+_LIBCPP_END_NAMESPACE_STD
