![]() ![]() ![]() In the single-pool approach, higher priority messages are always received and processed before lower priority messages. There are some semantic differences between a solution that uses a single pool of consumer processes (either with a single queue that supports messages that have different priorities or with multiple queues that each handle messages of a single priority), and a solution that uses multiple queues with a separate pool for each queue. This diagram illustrates the use of separate message queues for each priority:Ī variation on this strategy is to implement a single pool of consumers that check for messages on high priority queues first, and only after that start to fetch messages from lower priority queues. Higher priority queues can have a larger pool of consumers that run on faster hardware than lower priority queues. Each queue can have a separate pool of consumers. The application is responsible for posting messages to the appropriate queue. In systems that don't support priority-based message queues, an alternative solution is to maintain a separate queue for each priority. (See the Competing Consumers pattern.) The number of consumer processes can be scaled up and down based on demand. Most message queue implementations support multiple consumers. The messages in the queue are automatically reordered so that those that have a higher priority are received before those that have a lower priority. The application that's posting a message can assign a priority. ![]() However, some message queues support priority messaging. SolutionĪ queue usually is a first-in, first-out (FIFO) structure, and consumers typically receive messages in the same order that they're posted to the queue. These requests should be processed earlier than lower priority requests that were previously sent by the application. In some cases, though, it's necessary to prioritize specific requests. In many cases, the order in which requests are received by a service isn't important. In the cloud, a message queue is typically used to delegate tasks to background processing. Context and problemĪpplications can delegate specific tasks to other services, for example, to perform background processing or to integrate with other applications or services. This pattern is useful in applications that offer different service level guarantees to individual clients. T1 = threading.Prioritize requests sent to services so that requests with a higher priority are received and processed more quickly than those with a lower priority. Which will print something like the below: FirstAccess: (0, 0)įor this reason, if you want to use an object from the top of a PriorityQueue, you should assign that object to a name: from queue import PriorityQueue T1 = threading.Thread(target=queue_manip) Here's an example: from queue import PriorityQueue While holding onto the queue object would be even less threadsafe, because that queue object is "live" (see this answer), you can still run into issues when accessing the objects on the queue if you expect the object ordering to be static. The above answers show how to access the elements of a PriorityQueue, however there is some danger when accessing objects from the inner queue in a multithreaded manner (as mentioned at the end of HYRY's answer). TL DR - If you are are using the top item multiple times in a multithreaded environment, you should assign the item to a variable. ![]()
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