Semaphores

For general purpose resource management and synchronisation, a semaphore primitive is provided. poco provides both binary and counting semaphores for use within coroutines and ISRs.

Sempahores are a generalisation of mutexes and can be used for synchronisation between coroutines and ISRs, or for managing access to a shared resource with a specific number of instances.

For synchronisation between coroutines only, consider using Mutexes instead.

This functionality is available from the specific header <poco/semaphore.h>.

Creating a Semaphore

Semaphores can either be created statically or dynamically. This API provides the *_create and *_create_static variants for both types of semaphores.

• For binary semaphores, you can use semaphore_create_binary() or semaphore_create_binary_static().

• For counting semaphores, you can use semaphore_create() or semaphore_create_static().

Acquiring and Releasing

Sempahores can be acquired and released using the *_acquire and *_release functions. The exact function depends on the execution context of the caller.

• For coroutines, use semaphore_acquire() and semaphore_release() or the no wait variant semaphore_acquire_no_wait().

• For ISRs and code executed outside the scheduler, use semaphore_acquire_from_isr() and semaphore_release_from_isr().

Warning

Failure to release the semaphore may cause a deadlock, where all other coroutines will wait their defined timeout.