// Obtain permissions to read objects in the workspace. This obtains
// many permissions on the read access and should be called in
// conjunction with _releaseAllReadPermissions.
// This method suspends the calling thread until such permission
// has been obtained. Permission is granted unless either another
// thread has write permission, or there are threads that
// have requested write permission and not gotten it yet.
// @param count This is the number of read permissions desired on the
// workspace.
// @exception InternalErrorException If the calling thread is interrupted
// while waiting to re-acquire read permissions.
private synchronized void _reacquireReadPermissions(int count) {
// If the count argument is equal to zero, which means we would like
// the current thread to has read depth equal to 0, i.e. not a reader,
// then it's already trivially done, since this method call is always
// preceded by _releaseAllReadPermissions.
if (count == 0) {
return;
}
Thread current = Thread.currentThread();
AccessRecord record = null;
if (current == _lastReader) {
record = _lastReaderRecord;
} else {
record = _getAccessRecord(current, false);
}
if ((record == null) || (count > record.failedReadAttempts)) {
throw new InvalidStateException(
this, "Trying to reacquire " + "read permission not in record.");
}
// Go into an infinite 'while (true)' loop, and each time through
// the loop, check if the condition is satisfied to have the current
// thread as a writer. If not, then wait on the workspace. Upon
// re-awakening, iterate in the loop again to check if the condition
// is now satisfied.
while (true) {
// If the current thread has write permission, or if there
// are no pending write requests, then grant read permission.
if ((current == _writer) || ((_waitingWriteRequests == 0) && (_writer == null))) {
_numReaders++;
record.failedReadAttempts -= count;
record.readDepth = count;
return;
}
try {
wait();
} catch (InterruptedException ex) {
throw new InternalErrorException(
"Thread interrupted while waiting for read access!" + ex.getMessage());
}
}
}
/**
* Frees the thread of all the readAccesses on the workspace. The method _reacquireAllReadAccesses
* should be called after this method is called.
*
* @return The number of readAccess that the thread possessed on the workspace
*/
private synchronized int _releaseAllReadPermissions() {
// Find the current thread.
Thread current = Thread.currentThread();
AccessRecord record = null;
if (current == _lastReader) {
record = _lastReaderRecord;
} else {
record = _getAccessRecord(current, false);
}
if ((record == null) || (record.readDepth == 0)) {
// current thread is not a reader
return 0;
} else {
_numReaders--;
notifyAll();
int result = record.readDepth;
record.failedReadAttempts += result;
record.readDepth = 0;
return result;
}
}