#include <linux/futex.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <unistd.h>
#include "mutex.h"
#include <atomic>

void FutexWait(std::atomic<int> *value, uint64_t expected_value) {
    syscall(SYS_futex, value, FUTEX_WAIT_PRIVATE, expected_value, nullptr, nullptr, 0);
}

void FutexWake(std::atomic<int> *value, int count) {
    syscall(SYS_futex, value, FUTEX_WAKE_PRIVATE, count, nullptr, nullptr, 0);
}

void Mutex::Lock() {
    int c = 0;
    if (!val_.compare_exchange_strong(c, 1)) {
        c = val_.exchange(2);
        while (c != 0) {
            FutexWait(&val_, 2);
            c = val_.exchange(2);
        }
    }
}

void Mutex::Unlock() {
    if (val_.fetch_sub(1) != 1) {
        val_ = 0;
        FutexWake(&val_, 1);
    }
}