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Patch #572628: Optional timeouts for put and get.

This commit is contained in:
Martin v. Löwis 2002-10-15 15:11:13 +00:00
parent d98d25e22d
commit 77ac429eff
4 changed files with 137 additions and 36 deletions
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46
Doc/lib/libqueue.tex
View File

@ -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
of multithreading semantics, this is not reliable.
Return \code{True} if the queue is empty, \code{False} otherwise.
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
multithreading semantics, this is not reliable.
Return \code{True} if the queue is full, \code{False} otherwise.
Because of multithreading semantics, this is not reliable.
\end{methoddesc}
\begin{methoddesc}{put}{item\optional{, block}}
Put \var{item} into the queue. If optional argument \var{block} is 1
(the default), block if necessary until a free slot is available.
Otherwise (\var{block} is 0), put \var{item} on the queue if a free
\begin{methoddesc}{put}{item\optional{, block\optional{, timeout}}}
Put \var{item} into the queue. If optional args \var{block} is true
and \var{timeout} is None (the default), block if necessary until a
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}}
Remove and return an item from the queue. If optional argument
\var{block} is 1 (the default), block if necessary until an item is
available. Otherwise (\var{block} is 0), return an item if one is
immediately available, else raise the
\exception{Empty} exception.
\begin{methoddesc}{get}{\optional{block\optional{, timeout}}}
Remove and return an item from the queue. If optional args
\var{block} is true and \var{timeout} is None (the default),
block if necessary until an item is available. If \var{timeout} is
a positive number, it blocks at most \var{timeout} seconds and raises
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}

86
Lib/Queue.py
View File

@ -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
necessary until a free slot is available. Otherwise (block
is 0), put an item on the queue if a free slot is immediately
available, else raise the Full exception.
If optional args 'block' is true and 'timeout' is None (the default),
block if necessary until a free slot is available. If 'timeout' is
a positive number, it blocks at most 'timeout' seconds and raises
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
necessary until an item is available. Otherwise (block is 0),
return an item if one is immediately available, else raise the
Empty exception.
If optional args 'block' is true and 'timeout' is None (the default),
block if necessary until an item is available. If 'timeout' is
a positive number, it blocks at most 'timeout' seconds and raises
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).

39
Lib/test/test_queue.py
View File

@ -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)

2
Misc/NEWS
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@ -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.