vsync / spinlock / twalock.h

Ticketlock with waiting array (TWA).

Groups: Fair locks

To use the TWA lock, one must declare the global waiting array once in the program. Use TWALOCK_ARRAY_DECL to declare the array where convenient.

Example:

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

#define N            12
#define EXPECTED_VAL N

TWALOCK_ARRAY_DECL;
twalock_t g_lock = TWALOCK_INIT();

vuint32_t g_x = 0;
vuint32_t g_y = 0;

void *
run(void *args)
{
    twalock_acquire(&g_lock);
    g_x++;
    g_y++;
    twalock_release(&g_lock);

    (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;
}

References:

Dice and Kogan - [TWA - Ticket Locks Augmented with a Waiting Array, EuroPar-19]

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Macros

Macro	Description
TWALOCK_ARRAY_DECL	TWALOCK_ARRAY_DECL declares the global g_vtwa_array variable.
TWALOCK_INIT	Initializer of twalock_t.

Macro TWALOCK_ARRAY_DECL

TWALOCK_ARRAY_DECL declares the global g_vtwa_array variable.

Macro TWALOCK_INIT

TWALOCK_INIT()

Initializer of twalock_t.

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Functions

Function	Description
twalock_init	Initializes the given TWA lock.
twalock_acquire	Acquires the given TWA lock.
twalock_release	Releases the given TWA lock.
twalock_tryacquire	Tries to acquire the given TWA lock.

Function twalock_init

static void twalock_init(twalock_t *l)

Initializes the given TWA lock.

Parameters:

• l: address of twalock_t object.

Note: alternatively use TWALOCK_INIT

Function twalock_acquire

static void twalock_acquire(twalock_t *l)

Acquires the given TWA lock.

Parameters:

• l: address of twalock_t object.

Function twalock_release

static void twalock_release(twalock_t *l)

Releases the given TWA lock.

Parameters:

• l: address of twalock_t object.

Function twalock_tryacquire

static vbool_t twalock_tryacquire(twalock_t *l)

Tries to acquire the given TWA lock.

Parameters:

• l: address of twalock_t object.

Returns: true on success.

Returns: false on failure.

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