Method acquireRead

vrtManager/rwlock.py:63–108

Acquire a read lock for the current thread, waiting at most timeout seconds or doing a non-blocking check in case timeout is <= 0. In case timeout is None, the call to acquireRead blocks until the lock request can be serviced. In case the timeout expires before the

(self, timeout=None)

        self.__readers = {}

    def acquireRead(self, timeout=None):
        """Acquire a read lock for the current thread, waiting at most
        timeout seconds or doing a non-blocking check in case timeout is <= 0.

        In case timeout is None, the call to acquireRead blocks until the
        lock request can be serviced.

        In case the timeout expires before the lock could be serviced, a
        RuntimeError is thrown."""

        if timeout is not None:
            endtime = time() + timeout
        me = currentThread()
        self.__condition.acquire()
        try:
            if self.__writer is me:
                # If we are the writer, grant a new read lock, always.
                self.__writercount += 1
                return
            while True:
                if self.__writer is None:
                    # Only test anything if there is no current writer.
                    if self.__upgradewritercount or self.__pendingwriters:
                        if me in self.__readers:
                            # Only grant a read lock if we already have one
                            # in case writers are waiting for their turn.
                            # This means that writers can't easily get starved
                            # (but see below, readers can).
                            self.__readers[me] += 1
                            return
                        # No, we aren't a reader (yet), wait for our turn.
                    else:
                        # Grant a new read lock, always, in case there are
                        # no pending writers (and no writer).
                        self.__readers[me] = self.__readers.get(me, 0) + 1
                        return
                if timeout is not None:
                    remaining = endtime - time()
                    if remaining <= 0:
                        # Timeout has expired, signal caller of this.
                        raise RuntimeError("Acquiring read lock timed out")
                    self.__condition.wait(remaining)
                else:
                    self.__condition.wait()
        finally:
            self.__condition.release()

    def acquireWrite(self, timeout=None):
        """Acquire a write lock for the current thread, waiting at most