Written by daweibayu
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Thread API

最近在面试，遇到不少要手撕 Thread 相关的面试题，发现确实有不少东西还是模棱两可，所以写本文梳理一下线程相关逻辑。本文不重在线程相关的原理，而是使用。为了让本文更专注一点，所以只列 API。

pthread

不管是 Kotlin、Java 还是其他 JVM 语言，本身的线程都是由 Native 支持，所以先看一下 Native 的 API。

所谓的 pthread 即是 posix(Portable Operating System Interface) thread，相关的协议规范于 IEEE Std 1003，文档本身收费，其接口定义则由 The Open Group 维护，好在这个不收费，其中关于 pthread 的 api 位于 pthread.h。不论是哪种（NPTL、LinuxThreads、FreeBSD、Windows 等）实现，最终都要遵循这一规范。

和线程切换等相关的 api 如下：

int   pthread_create(pthread_t *, const pthread_attr_t *, void *(*)(void *), void *);
int   pthread_detach(pthread_t);
int   pthread_equal(pthread_t, pthread_t);
void  pthread_exit(void *);
int   pthread_cancel(pthread_t);
int   pthread_join(pthread_t, void **);


int   pthread_mutex_init(pthread_mutex_t *, const pthread_mutexattr_t *);
int   pthread_mutex_lock(pthread_mutex_t *);
int   pthread_mutex_destroy(pthread_mutex_t *);
int   pthread_mutex_trylock(pthread_mutex_t *);
int   pthread_mutex_unlock(pthread_mutex_t *);

int   pthread_cond_destroy(pthread_cond_t *);
int   pthread_cond_init(pthread_cond_t *, const pthread_condattr_t *);
int   pthread_cond_timedwait(pthread_cond_t *, pthread_mutex_t *, const struct timespec *);
int   pthread_cond_wait(pthread_cond_t *, pthread_mutex_t *);
int   pthread_cond_signal(pthread_cond_t *);
int   pthread_cond_broadcast(pthread_cond_t *);
int   pthread_once(pthread_once_t *, void (*)(void));

Java Thread

public final void join(long millis)
public void interrupt()
public synchronized void start()
public static void sleep(long millis)
public static native void yield();

suspend、resume、stop、destroy 等均以废弃。

 public final native void wait(long timeout, int nanos)
 @FastNative public final native void notifyAll();
 @FastNative public final native void notify();

void ObjectMonitor::wait(jlong millis) {
    pthread_mutex_lock(&_mutex);  // 加锁
    if (millis == 0) {
        pthread_cond_wait(&_cond, &_mutex);  // 无限期等待
    } else {
        struct timespec ts;
        clock_gettime(CLOCK_REALTIME, &ts);
        ts.tv_sec += millis / 1000;
        ts.tv_nsec += (millis % 1000) * 1000000;
        pthread_cond_timedwait(&_cond, &_mutex, &ts);  // 超时等待
    }
    pthread_mutex_unlock(&_mutex);  // 释放锁
}