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Nested semaphore locking

Posted by Nobody/Anonymous on March 6, 2006
Hello,

is there any simple way to extend FreeRTOS
semaphores to add nesting? Like in:

xSemaphoreTake(s, portMAX_DELAY); /* obtains s */
xSemaphoreTake(s, portMAX_DELAY); /* does not deadlock! */
xSemaphoreGive(s); /* does not free s */
xSemaphoreGive(s); /* really frees s */

I tried to implement it on top of FreeRTOS semaphores, but it's quite tricky.

RE: Nested semaphore locking

Posted by Nobody/Anonymous on March 6, 2006
I've solved the problem like this.
Does it look sane?

typedef struct Semaphore
{
xSemaphoreHandle lock;
xTaskHandle owner;
int nest_count;
} Semaphore;

void sem_obtain(struct Semaphore *s)
{
if (s->owner != xTaskGetCurrentTaskHandle())
xSemaphoreTake(s->lock, portMAX_DELAY);

s->owner = xTaskGetCurrentTaskHandle();
s->nest_count++;
}


void sem_release(struct Semaphore *s)
{
ASSERT(s->owner == xTaskGetCurrentTaskHandle());

if (--s->nest_count == 0)
{
/* Disown semaphore */
s->owner = NULL;
xSemaphoreGive(s->lock);
}
}

RE: Nested semaphore locking

Posted by Nobody/Anonymous on March 6, 2006
Probably very sane, as I don't really under stand it :-)


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