mutex_example

mutex_example

This program shows the usage of sharing data between an RT and a non-RT thread via the cactus_rt::mutex, which is a priority-inheritence mutex compatible with the Lockable interface. This means you can use this mutex just like you would a normal mutex from STL and expect that priority inheritance is enabled on it.

In this example, we use the cactus_rt::mutex to implement a very naive double buffer. It has 2 data slots guarded by the priority-inheriting mutex. The RT thread writes to the double buffer at 1 kHz and the non-RT thread reads it every half second. Once it is read, it is logged via the cactus_rt logging capability.

Note: a lockless version of this double buffer is implemented by the cactus-rt framework under cactus_rt::experimental::lockless::spsc::RealtimeWritableValue which doesn't require a lock. That serves as an alternative to this code without the usage of a mutex.

To run:

$ make debug
$ sudo build/debug/examples/mutex_example/rt_mutex_example

You should be able to see 4 values changing every 0.5s, and they are:

1. The elapsed time in nanoseconds.
2. The elapsed time in microseconds.
3. The output of the cosine function (amplitude = 1, period = 5 seconds).
4. The output of the cosine function times 10.

These 4 values are written by the RT thread into the double buffer and read from the non-RT thread from the double buffer live, so you should see the third column go from 1 -> -1 -> 1 every 5 seconds.