In computer science, message queues and mailboxes are software-engineering components typically used for inter-process communication (IPC), or for inter-thread communication within the same process. They use a queue for messaging the passing of control or of content. Group communication systems provide similar kinds of functionality.
The message queue paradigm is a sibling of the subscriber pattern, and is typically one part of a larger message-oriented middleware system. Most messaging systems support both the publisher/subscriber and message queue models in their API, e.g. Java Message Service (JMS).
Common message queue options
- Durability: messages may be kept in memory, written to disk, or even committed to a DBMS if the need for reliability indicates a more resource-intensive solution.
- Security policies: which applications should have access to these messages?
- Message purging policies: queues or messages may have a TTL.
- Message filtering: some systems support filtering data so that a subscriber may only see messages matching some pre-specified criteria of interest.
- Delivery policies: do we need to guarantee that a message is delivered at least once, or no more than once?
- Routing policies: in a system with many queue servers, what servers should receive a message or a queue’s messages?
- Batching policies: should messages be delivered immediately? Or should the system wait a bit and try to deliver many messages at once?
- Queuing criteria: when should a message be considered “enqueued”? When one queue has it? Or when it has been forwarded to at least one remote queue? Or to all queues?
- Receipt notification: A publisher may need to know when some or all subscribers have received a message