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/*
Copyright (C) 2009 Red Hat, Inc.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; 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
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