Add beast_basics module

modules/beast_basics/threads/beast_ReadWriteMutex.cpp

@@ -0,0 +1,111 @@
+/*============================================================================*/
+/*
+  VFLib: https://github.com/vinniefalco/VFLib
+
+  Copyright (C) 2008 by Vinnie Falco <vinnie.falco@gmail.com>
+
+  This library contains portions of other open source products covered by
+  separate licenses. Please see the corresponding source files for specific
+  terms.
+
+  VFLib is provided under the terms of The MIT License (MIT):
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files (the "Software"), to deal
+  in the Software without restriction, including without limitation the rights
+  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+  copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+  IN THE SOFTWARE.
+*/
+/*============================================================================*/
+
+ReadWriteMutex::ReadWriteMutex () noexcept
+{
+}
+
+ReadWriteMutex::~ReadWriteMutex () noexcept
+{
+}
+
+void ReadWriteMutex::enterRead () const noexcept
+{
+    for (;;)
+    {
+        // attempt the lock optimistically
+        // THIS IS NOT CACHE-FRIENDLY!
+        m_readers->addref ();
+
+        // is there a writer?
+        // THIS IS NOT CACHE-FRIENDLY!
+        if (m_writes->isSignaled ())
+        {
+            // a writer exists, give up the read lock
+            m_readers->release ();
+
+            // block until the writer is done
+            {
+                CriticalSection::ScopedLockType lock (m_mutex);
+            }
+
+            // now try the loop again
+        }
+        else
+        {
+            break;
+        }
+    }
+}
+
+void ReadWriteMutex::exitRead () const noexcept
+{
+    m_readers->release ();
+}
+
+void ReadWriteMutex::enterWrite () const noexcept
+{
+    // Optimistically acquire the write lock.
+    m_writes->addref ();
+
+    // Go for the mutex.
+    // Another writer might block us here.
+    m_mutex.enter ();
+
+    // Only one competing writer will get here,
+    // but we don't know who, so we have to drain
+    // readers no matter what. New readers will be
+    // blocked by the mutex.
+    //
+    if (m_readers->isSignaled ())
+    {
+        SpinDelay delay;
+
+        do
+        {
+            delay.pause ();
+        }
+        while (m_readers->isSignaled ());
+    }
+}
+
+void ReadWriteMutex::exitWrite () const noexcept
+{
+    // Releasing the mutex first and then decrementing the
+    // writer count allows another waiting writer to atomically
+    // acquire the lock, thus starving readers. This fulfills
+    // the write-preferencing requirement.
+
+    m_mutex.exit ();
+
+    m_writes->release ();
+}