Introduction

I know @kaspar030 is working on something like this too, but when I was working with lwIP again, I decided to port out the messaging layer I implemented for it, to better test it and to give it as an alternative to @kaspar030's work (and since it was already laying around in my repo it took me only half a day and some hours of boredom on Christmas to port it to msg_t).

mbox is thought to be an alternative - not a replacement - to standard-IPC. There are probably many ways to make it a little bit smaller in memory consumption, but I based it on the unix support for mbox of lwIP (with many adaptations to make it more RIOT-y) so it is quite stable.

Summary

mbox is a datatype with two base operations (of that there are some variations - more on that later):

• mbox_put() and
• mbox_get()

Blocking IPC

mbox_put() allows a user to put a msg_t in the mbox. If the mbox is full the thread will block and be signaled through the mbox::not_full semaphore, when there is space in the mbox again.

mbox_get() allows a user to get a msg_t from the mbox. If the mbox is empty the thread will block and be signaled through the mbox::not_empty semaphore, when another thread puts something in the mbox.

Non-blocking IPC

There is a non-blocking variant mbox_tryget() and mbox_tryput() for both operations, that just returns -EAGAIN when the normal operations would block (they don't require the semaphores, though they both post them, so the blocking variants are woken up).

mbox and time

Since the blocking mechanism is based on semaphores there is also a timeout-variant of mbox_get(): mbox_get_timed(). If we make this optional for semaphores we also can make it optional here.

Dependencies

Depends on #4551 and maybe #4374 (though I did not run into any problems during tests, regarding this bug).