Initial Commit

plexpy/lock.py

@@ -0,0 +1,87 @@
+"""
+Locking-related classes
+"""
+
+import plexpy.logger
+import time
+import threading
+import Queue
+
+
+class TimedLock(object):
+    """
+    Enforce request rate limit if applicable. This uses the lock so there
+    is synchronized access to the API. When N threads enter this method, the
+    first will pass trough, since there there was no last request recorded.
+    The last request time will be set. Then, the second thread will unlock,
+    and see that the last request was X seconds ago. It will sleep
+    (request_limit - X) seconds, and then continue. Then the third one will
+    unblock, and so on. After all threads finish, the total time will at
+    least be (N * request_limit) seconds. If some request takes longer than
+    request_limit seconds, the next unblocked thread will wait less.
+    """
+
+    def __init__(self, minimum_delta=0):
+        """
+        Set up the lock
+        """
+        self.lock = threading.Lock()
+        self.last_used = 0
+        self.minimum_delta = minimum_delta
+        self.queue = Queue.Queue()
+
+    def __enter__(self):
+        """
+        Called when with lock: is invoked
+        """
+        self.lock.acquire()
+        delta = time.time() - self.last_used
+        sleep_amount = self.minimum_delta - delta
+        if sleep_amount >= 0:
+            # zero sleeps give the cpu a chance to task-switch
+            plexpy.logger.debug('Sleeping %s (interval)', sleep_amount)
+            time.sleep(sleep_amount)
+        while not self.queue.empty():
+            try:
+                seconds = self.queue.get(False)
+                plexpy.logger.debug('Sleeping %s (queued)', seconds)
+                time.sleep(seconds)
+            except Queue.Empty:
+                continue
+            self.queue.task_done()
+
+    def __exit__(self, type, value, traceback):
+        """
+        Called when exiting the with block.
+        """
+        self.last_used = time.time()
+        self.lock.release()
+
+    def snooze(self, seconds):
+        """
+        Asynchronously add time to the next request. Can be called outside
+        of the lock context, but it is possible for the next lock holder
+        to not check the queue until after something adds time to it.
+        """
+        # We use a queue so that we don't have to synchronize
+        # across threads and with or without locks
+        plexpy.logger.info('Adding %s to queue', seconds)
+        self.queue.put(seconds)
+
+
+class FakeLock(object):
+    """
+    If no locking or request throttling is needed, use this
+    """
+
+    def __enter__(self):
+        """
+        Do nothing on enter
+        """
+        pass
+
+    def __exit__(self, type, value, traceback):
+        """
+        Do nothing on exit
+        """
+        pass