12.2. Multi-threaded communication: Queue

Queue

• What is a queue: a special structure, similar to a list. But just like in a queue, once the elements in the queues are removed, they are removed from the queue.
• Communication between threads can be done using queue queues
• How the thread uses the queue. Queue "There are other types of objects to talk about below" to communicate:
• 1. Create a Queue object: Object =queue. Queue (x), X is the queued capacity, X can not be filled, the default is no capacity limit,
• 2.get () allows a thread to get an element from the queue, if the queue is empty, get waits, get can set the timeout parameter, which is the wait time
• 3.put () can put an element into the queue "the default queue is first-in, first-out, first-placed elements will be taken out first", if the queue is full, put will wait, put can set the timeout parameter, which is the wait time

The following example is: Sender thread sends diameter to Recvder thread, Recvder calculates perimeter "

ImportThreading,time,queue,randomdefSender ():#Sender Send diameter     whiletrue:x=random.randint (1,10)        Print("Send done:", X) q.put (x)#put a random number on each secondTime.sleep (1)#Put a A in every seconddefRecvder ():#recvder Calculate Perimeter    whiletrue:x=Q.get ()Print("recv Done:", x*3.14)#Take out an element every second and calculate the resultTime.sleep (1) Q=queue. Queue () T1=threading. Thread (target=sender) T2=threading. Thread (target=recvder) T1.start () T2.start () T1.join () T2.join ()

• The Queue object already contains the necessary locks, so do not worry about errors

ImportThreading,time,queue,randomdefSender ():#Sender Send diameter     whiletrue:x=random.randint (1,10)        Print("Send done:", X) q.put (x)#put a random number on each secondTime.sleep (1)#Put a A in every seconddefRecvder ():#recvder Calculate Perimeter    whiletrue:x=Q.get ()Print(Threading.current_thread (),"recv Done:", x*3.14)#Take out an element every second and calculate the resultTime.sleep (2) Q=queue. Queue () T1=threading. Thread (target=sender) T2=threading. Thread (target=recvder) T3=threading. Thread (target=recvder) T1.start () T2.start () T3.start () t1.join () t2.join () T3.join ()

Note:

Queues can have capacity limits:

Settings for timeout:

Other related functions of the queue "set Q as a queue object":

• Q.qsize (): Returns the number of elements in the current queue
• Q.empty (): Determines whether the queue is empty, returns a Boolean value
• Q.full (): Determines whether the queue is full, returns a Boolean value

• Q.get_nowait (): Use Get () directly, if there is no element in the queue, then it will block wait, after using get_nowait (), if there is no element in the queue, then an error will be
• Q.put_nowait (): Direct use put (), if the queue is full, then will block wait, using put_nowait (), if the queue is full, then will be an error

• Q.task_done (): After completing a work, the Task_done () function sends a signal to the queue that the task has completed "functions similar to: There is a single-plank bridge that can only load one person, a came to find B in the bridges, so a can not on the bridge, he is waiting, wait until B after the bridge shout him, He knew B had finished the bridge. "Q.task_done is mainly used in conjunction with Q.join ()
• Q.join (): actually means waiting until the queue is empty, and then performing another operation "you need to call Task_done after each get, until all the queues are empty, then the join below is executed"

ImportThreading,queue,time"""This example is: Manufacturers with the driver agreed, the production of 3, the driver to pull, and a pull away, only when 3 are pulled away, manufacturers continue to produce"""defProducer ():#Manufacturers     whileTrue: forIinchRange (3): Q.put (i) start_time=time.time () q.join ( )##结果显示join这里堵塞住了厂家线程        Print("Wait Time:", Time.time ()-start_time)#used to test for blockage, proving not because the driver's sleep jam is runningdefDriver ():#Old driver     whileTrue: forIinchRange (3):            Print(Q.get ()) Q.task_done ()Print("") Time.sleep (2) Q=queue. Queue () T1=threading. Thread (target=producer) T2=threading. Thread (target=driver) T1.start () T2.start () T1.join () T2.join ()

In the queue, there are other queues, and here are some common ones:

• A queue is a first-in, first-out line:

• The Lifoqueue is the back-in-first-out queue:

• Priorityqueue is the order in which elements are determined by the precedence specified when the element is loaded:
• Create method: Queue Object =queue. Priorityqueue ()
• Priority is small priority, but cannot be mixed, str can only be sorted with str, int can only be sorted with int
• The priorityqueue put parameter is a tuple in the format: Queue object. Put ((priority, data))

• The deque is a double-ended queue that allows first-in, first-out and back-to-back, i.e. both ends can be
• Because the double-ended queue is not practical, and the list is not very different, do not elaborate here, we can refer to: https://www.cnblogs.com/zhenwei66/p/6598996.html

12.2. Multi-threaded communication: Queue