mutex.c

#include <clod/thread.h>
#include <clod/sys/futex.h>
#include "debug.h"
#include "yield.h"
 
#define FUTEX_TIMEOUT_US (1000 * 1000)
 
#define ZERO 0
#define LOCKED 1
#define WAITER 2
 
void clod_mutex_lock(clod_mutex *mutex) {
    while (1) {
        int lock = clod_atomic_load(mutex);
        while (lock & LOCKED) {
            for (int i = 0; i < 500 && lock & LOCKED; i++) {
                clod_pause();
                lock = clod_atomic_load(mutex);
            }
 
            if (lock & LOCKED && clod_atomic_cas(mutex, &lock, lock + WAITER)) {
                clod_futex_wait(mutex, lock + WAITER, FUTEX_TIMEOUT_US);
                lock = clod_atomic_add(mutex, -WAITER);
            }
        }
 
        if (clod_atomic_cas(mutex, &lock, lock + 1))
            return;
    }
}
 
void clod_mutex_unlock(clod_mutex *mutex) {
    #if CLOD_DEBUG_THREAD
    if (!(clod_atomic_load(mutex) & 1)) {
        debug(CLOD_DEBUG_THREAD, "called clod_mutex_unlock on an unlocked mutex.");
    }
    #endif
 
    int lock = clod_atomic_add(mutex, -1);
    if (lock) {
        clod_futex_wake_one(mutex);
    }
}