vsync / spinlock / semaphore.h

Counting Semaphore.

see vsync/spinlock/rwlock.h

Example:

#include <vsync/spinlock/semaphore.h>
#include <vsync/common/assert.h>
#include <pthread.h>
#include <stdio.h>

#define N             12
#define EXPECTED_VAL  N
#define NUM_RESOURCES 1

semaphore_t g_semaphore = SEMAPHORE_INIT(NUM_RESOURCES);
vuint32_t g_x           = 0;
vuint32_t g_y           = 0;

void *
run(void *args)
{
    semaphore_acquire(&g_semaphore, NUM_RESOURCES);
    g_x++;
    g_y++;
    semaphore_release(&g_semaphore, NUM_RESOURCES);
    (void)args;
    return NULL;
}

int
main(void)
{
    pthread_t threads[N];

    for (vsize_t i = 0; i < N; i++) {
        pthread_create(&threads[i], NULL, run, (void *)i);
    }

    for (vsize_t i = 0; i < N; i++) {
        pthread_join(threads[i], NULL);
    }

    ASSERT(g_x == EXPECTED_VAL);
    ASSERT(g_x == g_y);
    printf("Final value %u\n", g_x);
    return 0;
}

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Macros

Macro	Description
SEMAPHORE_INIT	Initializer of semaphore_t with n resources.

Macro SEMAPHORE_INIT

SEMAPHORE_INIT(n)

Initializer of semaphore_t with n resources.

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Functions

Function	Description
semaphore_init	Initializes the semaphore.
semaphore_acquire	Acquires i resources of the semaphore if available.
semaphore_tryacquire	Tries to acquire i resources of the semaphore if available.
semaphore_release	Releases i resources of the semaphore.

Function semaphore_init

static void semaphore_init(semaphore_t *s, vuint32_t n)

Initializes the semaphore.

Parameters:

• s: address of semaphore_t object.
• n: number of resources.

Note: alternatively use SEMAPHORE_INIT

Function semaphore_acquire

static void semaphore_acquire(semaphore_t *s, vuint32_t i)

Acquires i resources of the semaphore if available.

other blocks until enough resources are available in the semaphore.

Parameters:

• s: address of semaphore_t object.
• i: number of resources to acquire.

Precondition: call semaphore_acquire with i <= N.

Function semaphore_tryacquire

static vbool_t semaphore_tryacquire(semaphore_t *s, vuint32_t i)

Tries to acquire i resources of the semaphore if available.

Parameters:

• s: address of semaphore_t object.
• i: number of resources to acquire.

Returns: true, if i resources were acquired.

Returns: false, if failed to acquire i resources.

Precondition: call semaphore_tryacquire with i <= N.

Function semaphore_release

static void semaphore_release(semaphore_t *s, vuint32_t i)

Releases i resources of the semaphore.

Parameters:

• s: address of semaphore_t object.
• i: number of resources to release.

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