address_based_sync.c

#include <stdint.h>
#include <threads.h>
#include <stdatomics.h>
#include <linux/futex.h>      /* Definition of FUTEX_* constants */
#include <sys/syscall.h>      /* Definition of SYS_* constants */
#include <unistd.h>
#include <errno.h>

static int futex(uint32_t *uaddr, int futex_op, uint32_t val, const struct timespec *timeout, uint32_t *uaddr2, uint32_t val3)
{
    return syscall(SYS_futex, uaddr, futex_op, val, timeout, uaddr2, val3);
}

static int address_wait(_Atomic uint32_t *addr, uint32_t *compare)
{
    if (atomic_load(addr) == *compare) {
        int ret = futex(addr, FUTEX_WAIT_PRIVATE, *compare, nullptr, nullptr, 0);
        if (ret == 0) {
            return thrd_success;
        } else {
            return thrd_error;
        }
    } else {
        return thrd_error;
    }
}

static int address_timedwait(_Atomic uint32_t* addr, uint32_t *compare, const struct timespec *restrict ts)
{
    if (atomic_load(addr) == *compare) {
        int ret = futex(addr, FUTEX_WAIT_BITSET_PRIVATE | FUTEX_CLOCK_REALTIME, *compare, ts, nullptr, FUTEX_BITSET_MATCH_ANY);
        if (ret == 0) {
                return thrd_success;
        } else if (ret == -1) {
                if (errno == ETIMEDOUT) {
                        return thrd_timeout;
                } else {
                        return thrd_error;
                }
        }
    } else {
        return thrd_success;
    }
}

static int address_signal(_Atomic uint32_t *addr)
{
    return futex((uint32_t *)addr, FUTEX_WAKE_BITSET_PRIVATE, 1, nullptr, nullptr, FUTEX_BITSET_MATCH_ANY);
}

static int address_broadcast(_Atomic uint32_t *addr)
{
        return futex((uint32_t *)addr, FUTEX_WAKE_BITSET_PRIVATE, 128, nullptr, nullptr, FUTEX_BITSET_MATCH_ANY);
}