fresh start

1 files changed, 120 insertions, 0 deletions

diff --git a/client/read_write_mutex.h b/client/read_write_mutex.h
new file mode 100644
index 00000000..721422e5
--- /dev/null
+++ b/client/read_write_mutex.h
@@ -0,0 +1,120 @@
+/*
+   Copyright (C) 2009 Red Hat, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2 of
+   the License, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef _H_READ_WRITE_MUTEX
+#define _H_READ_WRITE_MUTEX
+
+#include "threads.h"
+
+class ReadWriteMutex {
+public:
+    ReadWriteMutex()
+    {
+        _state.read_count = 0;
+        _state.write = false;
+        _state.write_waiting = false;
+    }
+
+    virtual ~ReadWriteMutex()
+    {
+    }
+
+    void read_lock()
+    {
+        Lock lock(_state_mutex);
+
+        while (_state.write || _state.write_waiting) {
+            _read_cond.wait(lock);
+        }
+
+        ++_state.read_count;
+    }
+
+    bool try_read_lock()
+    {
+        Lock lock(_state_mutex);
+        if (_state.write || _state.write_waiting) {
+            return false;
+        } else {
+            ++_state.read_count;
+            return true;
+        }
+    }
+
+    void read_unlock()
+    {
+        Lock lock(_state_mutex);
+        --_state.read_count;
+
+        if (!_state.read_count) { // last reader
+            _state.write_waiting = false;
+            release_waiters();
+        }
+    }
+
+    void write_lock()
+    {
+        Lock lock(_state_mutex);
+
+        while (_state.read_count || _state.write) {
+            _state.write_waiting = true;
+            _write_cond.wait(lock);
+        }
+        _state.write = true;
+    }
+
+    bool try_write_lock()
+    {
+        Lock lock(_state_mutex);
+
+        if (_state.read_count || _state.write) {
+            return false;
+        } else {
+            _state.write = true;
+            return true;
+        }
+    }
+
+    void write_unlock()
+    {
+        Lock lock(_state_mutex);
+        _state.write = false;
+        _state.write_waiting = false;
+        release_waiters();
+    }
+
+private:
+    void release_waiters()
+    {
+        _write_cond.notify_one();
+        _read_cond.notify_all();
+    }
+
+private:
+    struct {
+        unsigned int read_count;
+        bool write;
+        bool write_waiting;
+    } _state;
+
+    Mutex _state_mutex;
+    Condition _read_cond;
+    Condition _write_cond;
+};
+
+#endif
+