Atomsem.c File Reference

From EdWiki

Semaphore library.

This module implements a counting semaphore library with the following features:

  • Flexible blocking APIs
    Threads which wish to decrement a semaphore can choose whether to block, block with timeout, or not block if the semaphore has reached zero.
  • Interrupt-safe calls
    All APIs can be called from interrupt context. Any calls which could potentially block have optional parameters to prevent blocking if you wish to call them from interrupt context. Any attempt to make a call which would block from interrupt context will be automatically and safely prevented.
  • Priority-based queueing
    Where multiple threads are blocking on a semaphore, they are woken in order of the threads' priorities. Where multiple threads of the same priority are blocking, they are woken in FIFO order.
  • Count up to 255
    Semaphore counts can be initialised and incremented up to a maximum of 255.
  • Smart semaphore deletion
    Where a semaphore is deleted while threads are blocking on it, all blocking threads are woken and returned a status code to indicate the reason for being woken

All semaphore objects must be initialised before use by calling atomSemCreate(). Once initialised atomSemGet() and atomSemPut() are used to decrement and increment the semaphore count respectively.

If a semaphore count reaches zero, further calls to atomSemGet() will block the calling thread (unless the calling parameters request no blocking). If a call is made to atomSemPut() while threads are blocking on a zero-count semaphore, the highest priority thread is woken. Where multiple threads of the same priority are blocking, they are woken in the order in which the threads started blocking.

A semaphore which is no longer required can be deleted using atomSemDelete(). This function automatically wakes up any threads which are waiting on the deleted semaphore.

Notes: Note that those considering using a semaphore initialised to 1 for mutual exclusion purposes may wish to investigate the mutex library available in Atomthreads.

#include "atom.h"
#include "atomsem.h"
#include "atomtimer.h"

Data Structures

struct  sem_timer


typedef struct sem_timer SEM_TIMER


uint8_t atomSemCreate(ATOM_SEM *sem, uint8_t initial_count)
uint8_t atomSemDelete(ATOM_SEM *sem)
uint8_t atomSemGet(ATOM_SEM *sem, int32_t timeout)
uint8_t atomSemPut(ATOM_SEM *sem)
uint8_t atomSemResetCount(ATOM_SEM *sem, uint8_t count)