Java线程——Thread

线程Thread

Java的线程对应OS中的线程，相当于对OS线程的封装

作用	线程
JVM的基本操作 如 自动内存管理、取消偏向锁 线程dump、线程挂起等	VM Thread
负责执行定时操作	Periodic task Thread
负责垃圾回收	GC Thread
负责将字节码编译为本地代码	Compiler Thread
负责响应JVM外部信号	Singal Dispatcher Thread

意义	成员变量	类型
线程ID	tid	long
线程序列数	threadSeqNumber	static long
线程名	name	String
优先级	priority	int
是否守护线程	daemon	boolean
要执行的任务	target	Runnable
线程数组	group	ThreadGroup
状态码 New、Runnable、Bolcked、Waiting、Timed_Waiting、Terminated	threadStatus	int
线程对应的本地变量map	threadLocals	ThreadLocal.ThreadLocalMap

作用	API
创建线程	Thread(ThreadGroup group, Runnable target, String name, long stackSize)
启动	start
强制结束	stop
等待线程结束	join
当前线程进入等待	sleep
调用run方法	run
线程让步	yield
是否存活	isAlive
设置未捕获异常处理器	setUncaughtExceptionHandler
获取未捕获异常	getUncaughtException

UncaughtExceptionHandler 未捕获异常处理器，当线程发生非受检异常而终止时，JVM调用线程未捕获异常处理器的 uncaughtException方法

钩子

使用Runtime类的addShutdownHook(Thread hook)添加
ApplicationShutdownHooks.add(hook)
IdentityHashMap hooks.put(hook,hook)

源码解析（native方法就不解析了）

创建

构造函数调用init方法初始化线程

private void init(ThreadGroup g, Runnable target, String name,
                  long stackSize, AccessControlContext acc,
                  boolean inheritThreadLocals) {
    if (name == null) {
        throw new NullPointerException("name cannot be null");
    }

    this.name = name;

    Thread parent = currentThread();
    SecurityManager security = System.getSecurityManager();
    if (g == null) {
        //令securityManager获取当前线程的ThreadGroup
        if (security != null) {
            g = security.getThreadGroup();
        }

        //自行获取当前线程的ThreadGroup
        if (g == null) {
            g = parent.getThreadGroup();
        }
    }

    //确定权限——调用securityManager检查当前线程组是否拥有RuntimePermission("modifyThreadGroup")权限
    g.checkAccess();

    //确定权限——RuntimePermission("enableContextClassLoaderOverride")
    if (security != null) {
        if (isCCLOverridden(getClass())) {
            security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
        }
    }

    g.addUnstarted();

    this.group = g;
    this.daemon = parent.isDaemon();
    this.priority = parent.getPriority();
    if (security == null || isCCLOverridden(parent.getClass()))
        this.contextClassLoader = parent.getContextClassLoader();
    else
        this.contextClassLoader = parent.contextClassLoader;
    this.inheritedAccessControlContext =
        acc != null ? acc : AccessController.getContext();
    this.target = target;
    setPriority(priority);
    if (inheritThreadLocals && parent.inheritableThreadLocals != null)
        this.inheritableThreadLocals =
        ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
    /* Stash the specified stack size in case the VM cares */
    this.stackSize = stackSize;

    /* Set thread ID */
    tid = nextThreadID();
}

启动

public synchronized void start() {
    //状态必须为“NEW”
    if (threadStatus != 0)
        throw new IllegalThreadStateException();

    //添加至线程组
    group.add(this);

    boolean started = false;
    try {
        start0();
        started = true;
    } finally {
        try {
            if (!started) {
                group.threadStartFailed(this);
            }
        } catch (Throwable ignore) {
            /* do nothing. If start0 threw a Throwable then
                  it will be passed up the call stack */
        }
    }
}

private native void start0();

休眠

public static native void sleep(long millis) throws InterruptedException;

public static void sleep(long millis, int nanos)
    throws InterruptedException {
    if (millis < 0) {
        throw new IllegalArgumentException("timeout value is negative");
    }

    if (nanos < 0 || nanos > 999999) {
        throw new IllegalArgumentException(
            "nanosecond timeout value out of range");
    }

    if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
        millis++;
    }

    sleep(millis);
}

等待线程

public final synchronized void join(long millis)
    throws InterruptedException {
    long base = System.currentTimeMillis();
    long now = 0;

    if (millis < 0) {
        throw new IllegalArgumentException("timeout value is negative");
    }

    if (millis == 0) {
        while (isAlive()) {
            wait(0);
        }
    } else {
        while (isAlive()) {
            long delay = millis - now;
            if (delay <= 0) {
                break;
            }
            wait(delay);
            now = System.currentTimeMillis() - base;
        }
    }
}

让步

public static native void yield();