What have you used sysv/posix message queues for?

I've never seen any project or anything utilizing posix or sysv message queues - and being cu开发者_如何学Gorious, what problems or projects have you guys used them for ?

---

I had a series of commands that needed to be executed in order, but the main program flow did not depend on their completion so I queued them up and passed them to another process via a System V message queue to be executed independently of the main program. Since message queues provide an asynchronous communications protocol, they were a good fit for this task.

To be honest, I used System V message queues because I had never used them before and I wanted to. I'm sure there are other IPC methods I could have used.

---

It's been a while since I've done any real VxWorks programming, but you can also find message queues used in VxWorks applications. According to the VxWorks Application Programmer's Guide (Google search), the primary intertask communication mechanism within a single CPU is message queues. VxWorks uses two message queue subroutine libraries (POSIX and VxWorks).

---

I once wrote a text-mode I/O generator utility that had one thread in charge of updating the UI and a number of worker threads to do the actual I/O work. When a worker thread completed an I/O, it sent an update message to the UI thread. I implemented this message system using a POSIX message queue.

Why implement it like this? It sounded like a good idea at the time, and I was curious about how they worked. I figured I could solve the problem and learn something at the same time. There were many different techniques I could have used, and I don't suppose there was any profound reason why I chose this technique. I didn't realize it until later, but I was glad I used a POSIX queue when I had to port the utility to another system (it was also POSIX compliant, so I didn't have to worry about porting external libraries to get my app to run).

---

You can use it for IPC for sure because it is an IPC mechanism. With this mechanism you can write multi-process event processing applications in which all of the applications are using the queue and each of which are waiting for a special type of message (an special event to occur). When the message arrives that process takes the message, processes that and puts the result back into the queue so that the other process can use it.
Once i wrote such an application using message queues. It is pretty easy to work with and does not need Inter-process synchronization mechanisms such as semaphores. You can use it in place of Shared Memory of Memory Mapped files as well, in situations in which all you need is just sending a structure or some kind of packed data to other processes Message Queues are far easier to use than any other IPC mechanism.
This book contains all information you need to know about Message Queues and other IPC mechanisms in Linux.