python隊列queue模塊詳解

更新時間：2018年04月27日 09:50:49 作者：菜鳥磊子

這篇文章主要為大家詳細介紹了python隊列queue模塊的相關(guān)資料，具有一定的參考價值，感興趣的小伙伴們可以參考一下

隊列queue 多應(yīng)用在多線程應(yīng)用中，多線程訪問共享變量。對于多線程而言，訪問共享變量時，隊列queue是線程安全的。從queue隊列的具體實現(xiàn)中，可以看出queue使用了1個線程互斥鎖(pthread.Lock())，以及3個條件標量(pthread.condition()),來保證了線程安全。

queue隊列的互斥鎖和條件變量，可以參考另一篇文章：python線程中同步鎖

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

定義隊列時有一個默認的參數(shù)maxsize, 如果不指定隊列的長度，即manxsize=0,那么隊列的長度為無限長，如果定義了大于0的值，那么隊列的長度就是maxsize。

self._init(maxsize)：使用了python自帶的雙端隊列deque,來存儲元素。

self.mutex互斥鎖：任何獲取隊列的狀態(tài)(empty(),qsize()等)，或者修改隊列的內(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。同時該互斥鎖被三個共享變量同時享有，即操作conditiond時的require和release操作也就是操作了該互斥鎖。

self.not_full條件變量：當隊列中有元素添加后，會通知notify其他等待添加元素的線程，喚醒等待require互斥鎖，或者有線程從隊列中取出一個元素后，通知其它線程喚醒以等待require互斥鎖。

self.not empty條件變量：線程添加數(shù)據(jù)到隊列中后，會調(diào)用self.not_empty.notify()通知其它線程，喚醒等待require互斥鎖后，讀取隊列。

self.all_tasks_done條件變量：消費者線程從隊列中g(shù)et到任務(wù)后，任務(wù)處理完成，當所有的隊列中的任務(wù)處理完成后，會使調(diào)用queue.join()的線程返回，表示隊列中任務(wù)以處理完畢。

queue.put(self, item, block=True, timeout=None)函數(shù):

申請獲得互斥鎖，獲得后，如果隊列未滿，則向隊列中添加數(shù)據(jù)，并通知notify其它阻塞的某個線程，喚醒等待獲取require互斥鎖。如果隊列已滿，則會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):

從隊列中獲取任務(wù)，并且從隊列中移除此任務(wù)。首先嘗試獲取互斥鎖，獲取成功則隊列中g(shù)et任務(wù)，如果此時隊列為空，則wait等待生產(chǎn)者線程添加數(shù)據(jù)。get到任務(wù)后，會調(diào)用self.not_full.notify()通知生產(chǎn)者線程，隊列可以添加元素了。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():無阻塞的向隊列中添加任務(wù)，當隊列為滿時，不等待，而是直接拋出full異常，重點是理解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():無阻塞的向隊列中g(shù)et任務(wù)，當隊列為空時，不等待，而是直接拋出empty異常，重點是理解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 分別獲取隊列的長度，是否為空，是否已滿等：

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線性安全隊列（先進先出），還有優(yōu)先級隊列LifoQueue(后進先出)，也就是新添加的先被get到。PriorityQueue具有優(yōu)先級的隊列，即隊列中的元素是一個元祖類型，（優(yōu)先級級別，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，重點是理解互斥鎖，條件變量如果協(xié)同工作，保證隊列的線程安全。

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()

以上就是本文的全部內(nèi)容，希望對大家的學習有所幫助，也希望大家多多支持腳本之家。

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