Patch #572628: Optional timeouts for put and get.

Doc/lib/libqueue.tex

@@ -54,35 +54,47 @@ semantics, this number is not reliable.
 \end{methoddesc}
 
 \begin{methoddesc}{empty}{}
-Return \code{1} if the queue is empty, \code{0} otherwise.  Because
+Return \code{True} if the queue is empty, \code{False} otherwise.
-of multithreading semantics, this is not reliable.
+Becauseof multithreading semantics, this is not reliable.
 \end{methoddesc}
 
 \begin{methoddesc}{full}{}
-Return \code{1} if the queue is full, \code{0} otherwise.  Because of
+Return \code{True} if the queue is full, \code{False} otherwise.
-multithreading semantics, this is not reliable.
+Because of multithreading semantics, this is not reliable.
 \end{methoddesc}
 
-\begin{methoddesc}{put}{item\optional{, block}}
+\begin{methoddesc}{put}{item\optional{, block\optional{, timeout}}}
-Put \var{item} into the queue.  If optional argument \var{block} is 1
+Put \var{item} into the queue. If optional args \var{block} is true
-(the default), block if necessary until a free slot is available.
+and \var{timeout} is None (the default), block if necessary until a
-Otherwise (\var{block} is 0), put \var{item} on the queue if a free
+free slot is available. If \var{timeout} is a positive number, it
+blocks at most \var{timeout} seconds and raises the \exception{Full}
+exception if no free slot was available within that time.
+Otherwise (\var{block} is false), put an item on the queue if a free
 slot is immediately available, else raise the \exception{Full}
-exception.
+exception (\var{timeout} is ignored in that case).
+
+\versionadded[the timeout parameter]{2.3}
+
 \end{methoddesc}
 
 \begin{methoddesc}{put_nowait}{item}
-Equivalent to \code{put(\var{item}, 0)}.
+Equivalent to \code{put(\var{item}, False)}.
 \end{methoddesc}
 
-\begin{methoddesc}{get}{\optional{block}}
+\begin{methoddesc}{get}{\optional{block\optional{, timeout}}}
-Remove and return an item from the queue.  If optional argument
+Remove and return an item from the queue. If optional args
-\var{block} is 1 (the default), block if necessary until an item is
+\var{block} is true and \var{timeout} is None (the default),
-available.  Otherwise (\var{block} is 0), return an item if one is
+block if necessary until an item is available. If \var{timeout} is
-immediately available, else raise the
+a positive number, it blocks at most \var{timeout} seconds and raises
-\exception{Empty} exception.
+the \exception{Empty} exception if no item was available within that
+time. Otherwise (\var{block} is false), return an item if one is
+immediately available, else raise the \exception{Empty} exception
+(\var{timeout} is ignored in that case).
+
+\versionadded[the timeout parameter]{2.3}
+
 \end{methoddesc}
 
 \begin{methoddesc}{get_nowait}{}
-Equivalent to \code{get(0)}.
+Equivalent to \code{get(False)}.
 \end{methoddesc}

Lib/Queue.py

@@ -1,5 +1,7 @@
 """A multi-producer, multi-consumer queue."""
 
+from time import time as _time, sleep as _sleep
+
 class Empty(Exception):
     "Exception raised by Queue.get(block=0)/get_nowait()."
     pass
@@ -29,29 +31,54 @@ class Queue:
         return n
 
     def empty(self):
-        """Return 1 if the queue is empty, 0 otherwise (not reliable!)."""
+        """Return True if the queue is empty, False otherwise (not reliable!)."""
         self.mutex.acquire()
         n = self._empty()
         self.mutex.release()
         return n
 
     def full(self):
-        """Return 1 if the queue is full, 0 otherwise (not reliable!)."""
+        """Return True if the queue is full, False otherwise (not reliable!)."""
         self.mutex.acquire()
         n = self._full()
         self.mutex.release()
         return n
 
-    def put(self, item, block=1):
+    def put(self, item, block=True, timeout=None):
         """Put an item into the queue.
 
-        If optional arg 'block' is 1 (the default), block if
+        If optional args 'block' is true and 'timeout' is None (the default),
-        necessary until a free slot is available.  Otherwise (block
+        block if necessary until a free slot is available. If 'timeout' is
-        is 0), put an item on the queue if a free slot is immediately
+        a positive number, it blocks at most 'timeout' seconds and raises
-        available, else raise the Full exception.
+        the Full exception if no free slot was available within that time.
+        Otherwise ('block' is false), put an item on the queue if a free slot
+        is immediately available, else raise the Full exception ('timeout'
+        is ignored in that case).
         """
         if block:
-            self.fsema.acquire()
+            if timeout is None:
+                # blocking, w/o timeout, i.e. forever
+                self.fsema.acquire()
+            elif timeout >= 0:
+                # waiting max. 'timeout' seconds.
+                # this code snipped is from threading.py: _Event.wait():
+                # Balancing act:  We can't afford a pure busy loop, so we
+                # have to sleep; but if we sleep the whole timeout time,
+                # we'll be unresponsive.  The scheme here sleeps very
+                # little at first, longer as time goes on, but never longer
+                # than 20 times per second (or the timeout time remaining).
+                delay = 0.0005 # 500 us -> initial delay of 1 ms
+                endtime = _time() + timeout
+                while True:
+                    if self.fsema.acquire(0):
+                        break
+                    remaining = endtime - _time()
+                    if remaining <= 0:  #time is over and no slot was free
+                        raise Full
+                    delay = min(delay * 2, remaining, .05)
+                    _sleep(delay)       #reduce CPU usage by using a sleep
+            else:
+                raise ValueError("'timeout' must be a positive number")
         elif not self.fsema.acquire(0):
             raise Full
         self.mutex.acquire()
@@ -80,18 +107,43 @@ class Queue:
         Only enqueue the item if a free slot is immediately available.
         Otherwise raise the Full exception.
         """
-        return self.put(item, 0)
+        return self.put(item, False)
 
-    def get(self, block=1):
+    def get(self, block=True, timeout=None):
         """Remove and return an item from the queue.
 
-        If optional arg 'block' is 1 (the default), block if
+        If optional args 'block' is true and 'timeout' is None (the default),
-        necessary until an item is available.  Otherwise (block is 0),
+        block if necessary until an item is available. If 'timeout' is
-        return an item if one is immediately available, else raise the
+        a positive number, it blocks at most 'timeout' seconds and raises
-        Empty exception.
+        the Empty exception if no item was available within that time.
+        Otherwise ('block' is false), return an item if one is immediately
+        available, else raise the Empty exception ('timeout' is ignored
+        in that case).
         """
         if block:
-            self.esema.acquire()
+            if timeout is None:
+                # blocking, w/o timeout, i.e. forever
+                self.esema.acquire()
+            elif timeout >= 0:
+                # waiting max. 'timeout' seconds.
+                # this code snipped is from threading.py: _Event.wait():
+                # Balancing act:  We can't afford a pure busy loop, so we
+                # have to sleep; but if we sleep the whole timeout time,
+                # we'll be unresponsive.  The scheme here sleeps very
+                # little at first, longer as time goes on, but never longer
+                # than 20 times per second (or the timeout time remaining).
+                delay = 0.0005 # 500 us -> initial delay of 1 ms
+                endtime = _time() + timeout
+                while 1:
+                    if self.esema.acquire(0):
+                        break
+                    remaining = endtime - _time()
+                    if remaining <= 0:  #time is over and no element arrived
+                        raise Empty
+                    delay = min(delay * 2, remaining, .05)
+                    _sleep(delay)       #reduce CPU usage by using a sleep
+            else:
+                raise ValueError("'timeout' must be a positive number")
         elif not self.esema.acquire(0):
             raise Empty
         self.mutex.acquire()
@@ -115,10 +167,10 @@ class Queue:
     def get_nowait(self):
         """Remove and return an item from the queue without blocking.
 
-        Only get an item if one is immediately available.  Otherwise
+        Only get an item if one is immediately available. Otherwise
         raise the Empty exception.
         """
-        return self.get(0)
+        return self.get(False)
 
     # Override these methods to implement other queue organizations
     # (e.g. stack or priority queue).

Lib/test/test_queue.py

@@ -60,17 +60,23 @@ def FailingQueueTest(q):
         raise RuntimeError, "Call this function with an empty queue"
     for i in range(queue_size-1):
         q.put(i)
-    q.fail_next_put = True
     # Test a failing non-blocking put.
+    q.fail_next_put = True
     try:
         q.put("oops", block=0)
         raise TestFailed("The queue didn't fail when it should have")
     except FailingQueueException:
         pass
+    q.fail_next_put = True
+    try:
+        q.put("oops", timeout=0.1)
+        raise TestFailed("The queue didn't fail when it should have")
+    except FailingQueueException:
+        pass
     q.put("last")
     verify(q.full(), "Queue should be full")
-    q.fail_next_put = True
     # Test a failing blocking put
+    q.fail_next_put = True
     try:
         _doBlockingTest( q.put, ("full",), q.get, ())
         raise TestFailed("The queue didn't fail when it should have")
@@ -79,6 +85,16 @@ def FailingQueueTest(q):
     # Check the Queue isn't damaged.
     # put failed, but get succeeded - re-add
     q.put("last")
+    # Test a failing timeout put
+    q.fail_next_put = True
+    try:
+        _doBlockingTest( q.put, ("full", True, 0.2), q.get, ())
+        raise TestFailed("The queue didn't fail when it should have")
+    except FailingQueueException:
+        pass
+    # Check the Queue isn't damaged.
+    # put failed, but get succeeded - re-add
+    q.put("last")
     verify(q.full(), "Queue should be full")
     q.get()
     verify(not q.full(), "Queue should not be full")
@@ -98,6 +114,13 @@ def FailingQueueTest(q):
     except FailingQueueException:
         pass
     verify(not q.empty(), "Queue should not be empty")
+    q.fail_next_get = True
+    try:
+        q.get(timeout=0.1)
+        raise TestFailed("The queue didn't fail when it should have")
+    except FailingQueueException:
+        pass
+    verify(not q.empty(), "Queue should not be empty")
     q.get()
     verify(q.empty(), "Queue should be empty")
     q.fail_next_get = True
@@ -128,8 +151,14 @@ def SimpleQueueTest(q):
         raise TestFailed("Didn't appear to block with a full queue")
     except Queue.Full:
         pass
+    try:
+        q.put("full", timeout=0.1)
+        raise TestFailed("Didn't appear to time-out with a full queue")
+    except Queue.Full:
+        pass
     # Test a blocking put
     _doBlockingTest( q.put, ("full",), q.get, ())
+    _doBlockingTest( q.put, ("full", True, 0.2), q.get, ())
     # Empty it
     for i in range(queue_size):
         q.get()
@@ -139,8 +168,14 @@ def SimpleQueueTest(q):
         raise TestFailed("Didn't appear to block with an empty queue")
     except Queue.Empty:
         pass
+    try:
+        q.get(timeout=0.1)
+        raise TestFailed("Didn't appear to time-out with an empty queue")
+    except Queue.Empty:
+        pass
     # Test a blocking get
     _doBlockingTest( q.get, (), q.put, ('empty',))
+    _doBlockingTest( q.get, (True, 0.2), q.put, ('empty',))
 
 def test():
     q=Queue.Queue(queue_size)

Misc/NEWS

@@ -348,6 +348,8 @@ Extension modules
 Library
 -------
 
+- Queue.Queue.{put,get} now support an optional timeout argument.
+
 - Various features of Tk 8.4 are exposed in Tkinter.py. The multiple
   option of tkFileDialog is exposed as function askopenfile{,name}s.