iTron data-queue in linux

Question

In iTron there is lighter version of the message-queue called data-queue. They are very easy to use for fast message transfers. Is there any equivalent synchronization primitive in Linux?

Definition of data-queue: It is a queue for one word messages

Answer 1

I don't know of any such primitive. I implemented an atomic queue using POSIX semaphores.

Answer 2

On the few occassions I have needed to implement my own message queue, I tend to use 1 semaphore and 1 mutex(or semaphore) for each queue. I have only dealt with thread level queues, so this probably doesn't apply if you want a queue between two processes.

The semaphore is used to count the number of messages in the queue and provide the OS mechanism for thread to suspend/wait upon new messages.

The mutex is used to protect the overall queue structure.

So, it might look a bit like this (very much pseudo code):

DataQueueRx( Queue*, WORD*, timeout? )
{
   WaitOnSemaphore( Queue->sema, timeout? );  //get token
   LockMutex
   {
      //manipulate your queue, and transfer the data to WORD
   } 
   ReleaseMutex
}

DataQueueTx( Queue*, WORD )
{
   LockMutex
   {
      //manipulate your queue, inserting new WORD msg

      ReleaseSemaphore(Queue->sema);  //increment semaphore count
   }
   UnlockMutex
}

However, perhaps this isn't very "light weight". This also assumes that queues are not destroyed while in use. Also, I suspect that with a "WORD" only queue, there could be some optimizations.

If you are seeking "Lock-free code", then I suggest spending a day or two reading through these articles by Sutter.

Good luck!