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隊(duì)列queue 多應(yīng)用在多線(xiàn)程應(yīng)用中，多線(xiàn)程訪(fǎng)問(wèn)共享變量。對(duì)于多線(xiàn)程而言，訪(fǎng)問(wèn)共享變量時(shí)，隊(duì)列queue是線(xiàn)程安全的。從queue隊(duì)列的具體實(shí)現(xiàn)中，可以看出queue使用了1個(gè)線(xiàn)程互斥鎖(pthread.Lock())，以及3個(gè)條件標(biāo)量(pthread.condition()),來(lái)保證了線(xiàn)程安全。
queue隊(duì)列的互斥鎖和條件變量，可以參考另一篇文章：python線(xiàn)程中同步鎖
queue的用法如下：
import Queque a=[1,2,3] device_que=Queque.queue() device_que.put(a) device=device_que.get()
先看看它的初始化函數(shù)__init__(self,maxsize=0):
def __init__(self, maxsize=0): self.maxsize = maxsize self._init(maxsize) # mutex must be held whenever the queue is mutating. All methods # that acquire mutex must release it before returning. mutex # is shared between the three conditions, so acquiring and # releasing the conditions also acquires and releases mutex. self.mutex = _threading.Lock() # Notify not_empty whenever an item is added to the queue; a # thread waiting to get is notified then. self.not_empty = _threading.Condition(self.mutex) # Notify not_full whenever an item is removed from the queue; # a thread waiting to put is notified then. self.not_full = _threading.Condition(self.mutex) # Notify all_tasks_done whenever the number of unfinished tasks # drops to zero; thread waiting to join() is notified to resume self.all_tasks_done = _threading.Condition(self.mutex) self.unfinished_tasks = 0
定義隊(duì)列時(shí)有一個(gè)默認(rèn)的參數(shù)maxsize, 如果不指定隊(duì)列的長(zhǎng)度，即manxsize=0,那么隊(duì)列的長(zhǎng)度為無(wú)限長(zhǎng)，如果定義了大于0的值，那么隊(duì)列的長(zhǎng)度就是maxsize。
self._init(maxsize)：使用了python自帶的雙端隊(duì)列deque,來(lái)存儲(chǔ)元素。
self.mutex互斥鎖：任何獲取隊(duì)列的狀態(tài)(empty(),qsize()等)，或者修改隊(duì)列的內(nèi)容的操作(get,put等)都必須持有該互斥鎖。共有兩種操作require獲取鎖，release釋放鎖。同時(shí)該互斥鎖被三個(gè)共享變量同時(shí)享有，即操作conditiond時(shí)的require和release操作也就是操作了該互斥鎖。
self.not_full條件變量：當(dāng)隊(duì)列中有元素添加后，會(huì)通知notify其他等待添加元素的線(xiàn)程，喚醒等待require互斥鎖，或者有線(xiàn)程從隊(duì)列中取出一個(gè)元素后，通知其它線(xiàn)程喚醒以等待require互斥鎖。
self.not empty條件變量：線(xiàn)程添加數(shù)據(jù)到隊(duì)列中后，會(huì)調(diào)用self.not_empty.notify()通知其它線(xiàn)程，喚醒等待require互斥鎖后，讀取隊(duì)列。
self.all_tasks_done條件變量：消費(fèi)者線(xiàn)程從隊(duì)列中g(shù)et到任務(wù)后，任務(wù)處理完成，當(dāng)所有的隊(duì)列中的任務(wù)處理完成后，會(huì)使調(diào)用queue.join()的線(xiàn)程返回，表示隊(duì)列中任務(wù)以處理完畢。
queue.put(self, item, block=True, timeout=None)函數(shù):
申請(qǐng)獲得互斥鎖，獲得后，如果隊(duì)列未滿(mǎn)，則向隊(duì)列中添加數(shù)據(jù)，并通知notify其它阻塞的某個(gè)線(xiàn)程，喚醒等待獲取require互斥鎖。如果隊(duì)列已滿(mǎn)，則會(huì)wait等待。最后處理完成后釋放互斥鎖。其中還有阻塞block以及非阻塞，超時(shí)等邏輯，可以自己看一下:
def put(self, item, block=True, timeout=None):
"""Put an item into the queue.
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 non-negative 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).
"""
self.not_full.acquire()
try:
if self.maxsize > 0:
if not block:
if self._qsize() == self.maxsize:
raise Full
elif timeout is None:
while self._qsize() == self.maxsize:
self.not_full.wait()
elif timeout < 0:
raise ValueError("'timeout' must be a non-negative number")
else:
endtime = _time() + timeout
while self._qsize() == self.maxsize:
remaining = endtime - _time()
if remaining <= 0.0:
raise Full
self.not_full.wait(remaining)
self._put(item)
self.unfinished_tasks += 1
self.not_empty.notify()
finally:
self.not_full.release()
queue.get(self, block=True, timeout=None)函數(shù):
從隊(duì)列中獲取任務(wù)，并且從隊(duì)列中移除此任務(wù)。首先嘗試獲取互斥鎖，獲取成功則隊(duì)列中g(shù)et任務(wù)，如果此時(shí)隊(duì)列為空，則wait等待生產(chǎn)者線(xiàn)程添加數(shù)據(jù)。get到任務(wù)后，會(huì)調(diào)用self.not_full.notify()通知生產(chǎn)者線(xiàn)程，隊(duì)列可以添加元素了。最后釋放互斥鎖。
def get(self, block=True, timeout=None):
"""Remove and return an item from the queue.
If optional args 'block' is true and 'timeout' is None (the default),
block if necessary until an item is available. If 'timeout' is
a non-negative 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).
"""
self.not_empty.acquire()
try:
if not block:
if not self._qsize():
raise Empty
elif timeout is None:
while not self._qsize():
self.not_empty.wait()
elif timeout < 0:
raise ValueError("'timeout' must be a non-negative number")
else:
endtime = _time() + timeout
while not self._qsize():
remaining = endtime - _time()
if remaining <= 0.0:
raise Empty
self.not_empty.wait(remaining)
item = self._get()
self.not_full.notify()
return item
finally:
self.not_empty.release()
queue.put_nowait():無(wú)阻塞的向隊(duì)列中添加任務(wù)，當(dāng)隊(duì)列為滿(mǎn)時(shí)，不等待，而是直接拋出full異常，重點(diǎn)是理解block=False:
def put_nowait(self, item): """Put an item into the queue without blocking. Only enqueue the item if a free slot is immediately available. Otherwise raise the Full exception. """ return self.put(item, False)
queue.get_nowait():無(wú)阻塞的向隊(duì)列中g(shù)et任務(wù)，當(dāng)隊(duì)列為空時(shí)，不等待，而是直接拋出empty異常，重點(diǎn)是理解block=False:
def get_nowait(self): """Remove and return an item from the queue without blocking. Only get an item if one is immediately available. Otherwise raise the Empty exception. """ return self.get(False)
queue.qsize empty full 分別獲取隊(duì)列的長(zhǎng)度，是否為空，是否已滿(mǎn)等：
def qsize(self): """Return the approximate size of the queue (not reliable!).""" self.mutex.acquire() n = self._qsize() self.mutex.release() return n def empty(self): """Return True if the queue is empty, False otherwise (not reliable!).""" self.mutex.acquire() n = not self._qsize() self.mutex.release() return n def full(self): """Return True if the queue is full, False otherwise (not reliable!).""" self.mutex.acquire() n = 0 < self.maxsize == self._qsize() self.mutex.release() return n
queue.join()阻塞等待隊(duì)列中任務(wù)全部處理完畢，需要配合queue.task_done使用：
def task_done(self):
"""Indicate that a formerly enqueued task is complete.
Used by Queue consumer threads. For each get() used to fetch a task,
a subsequent call to task_done() tells the queue that the processing
on the task is complete.
If a join() is currently blocking, it will resume when all items
have been processed (meaning that a task_done() call was received
for every item that had been put() into the queue).
Raises a ValueError if called more times than there were items
placed in the queue.
"""
self.all_tasks_done.acquire()
try:
unfinished = self.unfinished_tasks - 1
if unfinished <= 0:
if unfinished < 0:
raise ValueError('task_done() called too many times')
self.all_tasks_done.notify_all()
self.unfinished_tasks = unfinished
finally:
self.all_tasks_done.release()
def join(self):
"""Blocks until all items in the Queue have been gotten and processed.
The count of unfinished tasks goes up whenever an item is added to the
queue. The count goes down whenever a consumer thread calls task_done()
to indicate the item was retrieved and all work on it is complete.
When the count of unfinished tasks drops to zero, join() unblocks.
"""
self.all_tasks_done.acquire()
try:
while self.unfinished_tasks:
self.all_tasks_done.wait()
finally:
self.all_tasks_done.release()
Queue模塊除了queue線(xiàn)性安全隊(duì)列（先進(jìn)先出），還有優(yōu)先級(jí)隊(duì)列LifoQueue(后進(jìn)先出)，也就是新添加的先被get到。PriorityQueue具有優(yōu)先級(jí)的隊(duì)列，即隊(duì)列中的元素是一個(gè)元祖類(lèi)型，（優(yōu)先級(jí)級(jí)別，數(shù)據(jù)）。
class PriorityQueue(Queue): '''''Variant of Queue that retrieves open entries in priority order (lowest first). Entries are typically tuples of the form: (priority number, data). ''' def _init(self, maxsize): self.queue = [] def _qsize(self, len=len): return len(self.queue) def _put(self, item, heappush=heapq.heappush): heappush(self.queue, item) def _get(self, heappop=heapq.heappop): return heappop(self.queue) class LifoQueue(Queue): '''''Variant of Queue that retrieves most recently added entries first.''' def _init(self, maxsize): self.queue = [] def _qsize(self, len=len): return len(self.queue) def _put(self, item): self.queue.append(item) def _get(self): return self.queue.pop()
至此queue模塊介紹完畢，重點(diǎn)是理解互斥鎖，條件變量如果協(xié)同工作，保證隊(duì)列的線(xiàn)程安全。
下面是queue的完全代碼：
class Queue:
"""Create a queue object with a given maximum size.
If maxsize is <= 0, the queue size is infinite.
"""
def __init__(self, maxsize=0):
self.maxsize = maxsize
self._init(maxsize)
# mutex must be held whenever the queue is mutating. All methods
# that acquire mutex must release it before returning. mutex
# is shared between the three conditions, so acquiring and
# releasing the conditions also acquires and releases mutex.
self.mutex = _threading.Lock()
# Notify not_empty whenever an item is added to the queue; a
# thread waiting to get is notified then.
self.not_empty = _threading.Condition(self.mutex)
# Notify not_full whenever an item is removed from the queue;
# a thread waiting to put is notified then.
self.not_full = _threading.Condition(self.mutex)
# Notify all_tasks_done whenever the number of unfinished tasks
# drops to zero; thread waiting to join() is notified to resume
self.all_tasks_done = _threading.Condition(self.mutex)
self.unfinished_tasks = 0
def task_done(self):
"""Indicate that a formerly enqueued task is complete.
Used by Queue consumer threads. For each get() used to fetch a task,
a subsequent call to task_done() tells the queue that the processing
on the task is complete.
If a join() is currently blocking, it will resume when all items
have been processed (meaning that a task_done() call was received
for every item that had been put() into the queue).
Raises a ValueError if called more times than there were items
placed in the queue.
"""
self.all_tasks_done.acquire()
try:
unfinished = self.unfinished_tasks - 1
if unfinished <= 0:
if unfinished < 0:
raise ValueError('task_done() called too many times')
self.all_tasks_done.notify_all()
self.unfinished_tasks = unfinished
finally:
self.all_tasks_done.release()
def join(self):
"""Blocks until all items in the Queue have been gotten and processed.
The count of unfinished tasks goes up whenever an item is added to the
queue. The count goes down whenever a consumer thread calls task_done()
to indicate the item was retrieved and all work on it is complete.
When the count of unfinished tasks drops to zero, join() unblocks.
"""
self.all_tasks_done.acquire()
try:
while self.unfinished_tasks:
self.all_tasks_done.wait()
finally:
self.all_tasks_done.release()
def qsize(self):
"""Return the approximate size of the queue (not reliable!)."""
self.mutex.acquire()
n = self._qsize()
self.mutex.release()
return n
def empty(self):
"""Return True if the queue is empty, False otherwise (not reliable!)."""
self.mutex.acquire()
n = not self._qsize()
self.mutex.release()
return n
def full(self):
"""Return True if the queue is full, False otherwise (not reliable!)."""
self.mutex.acquire()
n = 0 < self.maxsize == self._qsize()
self.mutex.release()
return n
def put(self, item, block=True, timeout=None):
"""Put an item into the queue.
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 non-negative 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).
"""
self.not_full.acquire()
try:
if self.maxsize > 0:
if not block:
if self._qsize() == self.maxsize:
raise Full
elif timeout is None:
while self._qsize() == self.maxsize:
self.not_full.wait()
elif timeout < 0:
raise ValueError("'timeout' must be a non-negative number")
else:
endtime = _time() + timeout
while self._qsize() == self.maxsize:
remaining = endtime - _time()
if remaining <= 0.0:
raise Full
self.not_full.wait(remaining)
self._put(item)
self.unfinished_tasks += 1
self.not_empty.notify()
finally:
self.not_full.release()
def put_nowait(self, item):
"""Put an item into the queue without blocking.
Only enqueue the item if a free slot is immediately available.
Otherwise raise the Full exception.
"""
return self.put(item, False)
def get(self, block=True, timeout=None):
"""Remove and return an item from the queue.
If optional args 'block' is true and 'timeout' is None (the default),
block if necessary until an item is available. If 'timeout' is
a non-negative 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).
"""
self.not_empty.acquire()
try:
if not block:
if not self._qsize():
raise Empty
elif timeout is None:
while not self._qsize():
self.not_empty.wait()
elif timeout < 0:
raise ValueError("'timeout' must be a non-negative number")
else:
endtime = _time() + timeout
while not self._qsize():
remaining = endtime - _time()
if remaining <= 0.0:
raise Empty
self.not_empty.wait(remaining)
item = self._get()
self.not_full.notify()
return item
finally:
self.not_empty.release()
def get_nowait(self):
"""Remove and return an item from the queue without blocking.
Only get an item if one is immediately available. Otherwise
raise the Empty exception.
"""
return self.get(False)
# Override these methods to implement other queue organizations
# (e.g. stack or priority queue).
# These will only be called with appropriate locks held
# Initialize the queue representation
def _init(self, maxsize):
self.queue = deque()
def _qsize(self, len=len):
return len(self.queue)
# Put a new item in the queue
def _put(self, item):
self.queue.append(item)
# Get an item from the queue
def _get(self):
return self.queue.popleft()
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