void RWLock_local::read_lock()
{
mutex.lock();
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
if (state.writerswaiting > 0 || state.writing > 0)
{
state.readerswaiting++;
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
while (state.writerswaiting > 0 || state.writing > 0)
okToRead.wait(mutex);
state.readerswaiting--;
}
state.reading++;
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
mutex.unlock();
}
void RWLock_local::upgrade_to_write()
{
mutex.lock();
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
state.reading--;
// try to cut in line
if (state.reading == 0) {
state.writing++;
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
return;
}
// cut & paste from write_lock()
if (state.writing > 0 || state.reading > 0) {
state.writerswaiting++;
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
while (state.writing > 0 || state.reading > 0)
okToWrite.wait(mutex);
state.writerswaiting--;
}
state.writing++;
}
void RWLock_local::read_unlock()
{
mutex.lock();
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
state.reading--;
if (state.writerswaiting > 0 && state.reading == 0)
okToWrite.notify_one();
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
mutex.unlock();
}
/* It's safe (and necessary) to simply convert this writer to a reader without
blocking */
void RWLock_local::downgrade_to_read()
{
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
state.writing--;
if (state.readerswaiting > 0)
okToRead.notify_all();
state.reading++;
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
mutex.unlock();
}
void RWLock_local::write_unlock()
{
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
state.writing--;
if (state.writerswaiting > 0)
okToWrite.notify_one();
else if (state.readerswaiting > 0)
okToRead.notify_all();
#ifdef DEBUG
CHECKSAFETY();
CHECKLIVENESS();
#endif
mutex.unlock();
}
