RWLock.cpp revision 617e2443dfc17fe44fd44c0675d6aad2ffc9df42
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "RWLock.h"
RWLock::RWLock() : _counter(0) {}
void RWLock::acquire(const RWMode mode_p)
{
if (mode_p == READ_ONLY) {
//wait for writer's exit
_writeSem.acquire();
//might be blocked only to decrement _counter and _readSem.release() in release()
_countSem.acquire();
int tmp = ++_counter;
_countSem.release();
if (tmp == 1) {
//never blocks, no writers, first reader
_readSem.acquire();
}
_writeSem.release();
} else {
_writeSem.acquire();
//wait for reader's exit
_readSem.acquire();
}
return;
}
//will do nothing if no read-write lock was acquired
void RWLock::switch2RO()
{
_countSem.acquire();
if (!_counter) {
_counter = 1;
_writeSem.release();
}
_countSem.release();
}
//will do nothing if no lock was acquired
void RWLock::release()
{
//might be blocked only to increment _counter in read-only mode
_countSem.acquire();
if (_counter) {
//read-only mode
_counter--;
if (!_counter) {
//the last reader
_readSem.release();
}
} else {
//read-write mode
_readSem.release();
_writeSem.release();
}
_countSem.release();
return;
}