Python Queue接口的简单说明

2018-04-28

Queue是线程安全的

创建队列

Queue的初始化函数中可以指定队列的最大长度，默认值是0，表示队列长度为无限长。

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

向队列添加数据

首先申请获取互斥锁，获得后，如果队列未满，则向队列添加数据；如果队列已满，则等待。最后处理完成后释放互斥锁。
该方法带有两个额外的参数（block和timeout），用于控制队列已满时，是否阻塞线程，以及阻塞的最大时间。

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). 
    """

从队列中获取数据

首先申请获取互斥锁，获得后，如果队列中有数据，则取出数据，同时该数据从队列中移除。
该方法同样带有两个额外参数，用于控制队列为空时，是否阻塞线程，以及阻塞的最大时间。

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). 
    """

put_nowait/get_nowait

只是对put/get的一层封装而已。是否无阻塞的添加/获取数据。

qsize/empty/full

这三个方法分别获取队列的长度、是否是空队列、是否已满。