threading.Queue

Describing the queue Module

• The queue module implements various mulitproducer multiconsumer queues
• These can be used to safely exchange information between multiple threads

• The queue module defines three different queue classes:

  • Queue
  • LifoQueue
  • PriorityQueue
• An instance q of any of these constructors can be created

Describing Queue(maxsize=0)

• This class creates a FIFO queue
• maxsize is the maximum number of items that can be placed in the queue
• If maxsize is omitted or $0$, then the queue size is infinite

Describing LifoQueue(maxsize=0)

• This class creates a LIFO queue
• A LIFO queue is also known as a stack

Describing PriorityQueue(maxsize=0)

• This class creates a priority queue in which items are ordered from lowest to highest priority
• When working with this queue, items should be tuples
• These tuples should take the form of (priority, data)

Summarizing Instance Methods

• Each q instance should call get on the queue to retrieve a task

  • This call will block if no tasks are available
  • This will causes workers to go idle until one becomes available
• Then, the worker should execute the task
• Once the tasks is done, task_done shoul dbe called on q
• We can put tasks in q by calling put
• Calling join on q will wait until all pending tasks have completed

Benefit of Queues

• Using queues instead of thread pools has the following benefit:

  • Not creating threads, which is expensive
  • Not destroying threads, which is expensive
• The worker threads will run continuously
• When no tasks are in the queue, the queue will sleep
• This won't use any CPU time

References

• Python Essential References
• Documentation for Queue API
• Summarizing Methods of the Queue Class