MESSAGE QUEUE SYSTEM CODE

A distributed system should be robust enough to continue to operate when one or more nodes fail, stop working, lag or are taken down for maintenance. Now you might ask, what is a distributed system? It is an integrated system that spans multiple machines, clients or nodes which execute their tasks in parallel in a non-disruptive way. Message Queues are one of the best ways, if not the best, to That's a complex topic but to put it simply: Your thread would then go onto to process the rest of the messages as normal, provided no more messages from the critical thread are found. You can each time you check your queue for messages, first check for messages from the critical thread, and service those messages first. Say for instance that you consider messages from a time critical thread to be more important that other messages. Most message queue APIs also offer support for reading messages from the queue based on a filter that you designate. It also insures that a reader of the queue cannot read a partially written message from the queue. It insures that all writes to the queue are atomic. The message queue layer uses lower level synchronization schemes to insure that no two writers to the queue can write at the same time. For two-way use, after my thread sends a message to your thread, your thread may need to send data back to my thread via my message queue. For one-way use, my thread can use it to keep your thread appraised of key events in my thread, without acknowledgement back from your thread. Message queues can be used for both one-way and two-way, asynchronous messaging. The underlying message queue layer itself takes care of making sure that messages get into the queue without race conditions affecting the integrity of the queue. Message queues avoid needing to have a critical section or mutex shared between the two threads, or processes. Your code, when it gets around to it, reads the next message from the message queue, and then decides what to do about that message.

MESSAGE QUEUE SYSTEM CODE

An example: My thread or process can send a message to your message queue, and having sent it, my code goes on to do something else.

Message queue system