The futex_waitv syscall is a new syscall through which the process can wait for multiple futexes. The task wakes up when any futex in the list is awakened. This can be used to implement wait on multiple locks and wait lists, etc, without the limitations imposed by using eventfd. This k...
voidlock(int lockval){//trylock是用户级的自旋锁while(!trylock(lockval)){wait();//释放cpu,并将当期线程加入等待队列,是系统调用}}booleantrylock(int lockval){int i=0;//localval=1代表上锁成功while(!compareAndSet(lockval,0,1)){if(++i>10){returnfalse;}}returntrue;}voidunlock(int lockval)...
if(box64_futex_waitv) R_RAX=syscall(__NR_futex_waitv,R_RDI,R_RSI,R_RDX,R_R10,R_R8); else #endif R_RAX=(uint64_t)-ENOSYS; break; default: printf_log(LOG_INFO,"Error: Unsupported Syscall 0x%02Xh (%d)\n",s,s); emu->quit=1; ...
futexv = kcalloc(nr_futexes, sizeof(*futexv), GFP_KERNEL); if (!futexv) return -ENOMEM; if (!futexv) { ret = -ENOMEM; goto destroy_timer; } ret = futex_parse_waitv(futexv, waiters, nr_futexes); if (!ret) ret = futex_wait_multiple(futexv, nr_futexes, timeout ? &to :...
对于内核而言,futex是一个系统调用。当用户态出现锁竞争,线程需要休眠等待时,通过futex系统调用陷入内核并挂在wait queue中。当释放锁发现有线程在休眠等锁时,通过futex系统调用陷入内核去唤醒等锁的线程。 相比传统的SYSTEM V IPC机制,在无竞争时,用户态通过futex原子变量操作,替代内核对象操作,来提升性能。而绝大部...
（4）加锁的内存地址和值：v_ 变量 cpp源文件：在内部实现 futex函数，实现syscall调用。并提供wait和...
atomic_increment(mutex);while(1){// code-2if(atomic_test_set(mutex,1)==0){// 将mutex减1。atomic_decrement(mutex);return;}// code-3v=*mutex;// 检查mutex的最高位是不是0。if(v>0){continue;}// 把当前申请锁的线程加入申请锁的线程队列,然后阻塞这个线程。futex_wait(mutex,v);}}...
首先来看看FUTEX_WAIT的内核部分源码,如下: //linux kernel v4.6 kernel/futex.cstaticinlinevoidqueue_me(structfutex_q *q,structfutex_hash_bucket *hb)__releases(&hb->lock){intprio;// ... ... 省略plist_node_init(&q->list, prio);
Glibc中常用的线程同步方式举例: Semaphore 变量定义: sem_t sem; 初始化: sem_init(&sem,0,1); 进入加锁: sem_wait(&sem); 退出解锁: sem_post(&sem); Mutex 变量定义: pthread_mutex_t mut; 初始化: pthread_mutex_init(&mut,NULL); 进入加锁: pthread_mutex_lock(&mut); 退出解锁: pthread_mu...
当 进程尝试持有锁或者要进入互斥区的时候,对futex执行"down"操作,即原子性的给futex同步变量减1。如果同步变量变为0,则没有竞争发生, 进程照常执行。如果同步变量是个负数,则意味着有竞争发生,需要调用futex系统调用的futex_wait操作休眠当前进程。 当进程释放锁或 者要离开互斥区的时候,对futex进行"up"操作,即原...