Thread
一、源码
1、注册本地方法
private static native void registerNatives();
static {
registerNatives();
}
Java有两种方法：Java方法和本地方法。Java方法是由Java语言编写，编译成字节码，存储在class文件中。本地方法是由其他语言（比如C，C++，或者汇编）编写的，编译成和处理器相关的机器代码。本地方法保存在动态连接库中，格式是各个平台专有的。Java方法是平台无关的，单本地方法却不是。运行中的Java程序调用本地方法时，虚拟机装载包含这个本地方法的动态库，并调用这个方法。本地方法是联系Java程序和底层主机操作系统的连接方法
registerNatives()方法的作用就是注册除了registerNatives()以外的其他本地方法
2、属性
private volatile String name;
线程名称，volatile保证变量可见性
private int priority;
线程优先级
private boolean daemon = false;
默认不是守护线程
private Runnable target;
可执行的runnable
private ThreadGroup group;
当前线程的分组
private ClassLoader contextClassLoader;
thread的类加载器，方便有需要的父类加载器调用子类加载器，完成类的加载
private static int threadInitNumber;
private static synchronized int nextThreadNum() {
return threadInitNumber++;
}
默认的线程名称编号，全局唯一并递增，在没有指定线程名称时会被使用
ThreadLocal.ThreadLocalMap threadLocals = null; ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
线程的本地副本、线程父类的本地副本
private long stackSize;
可以手动设置线程的栈深度，默认0，有些虚拟机不支持
private long tid;
private static long threadSeqNumber;
private static synchronized long nextThreadID() {
return ++threadSeqNumber;
}
线程的id，全局唯一并递增，编号大于等于threadInitNumber
volatile Object parkBlocker
是给LockSupport使用的，控制线程阻塞
private volatile Interruptible blocker;
private final Object blockerLock = new Object();
void blockedOn(Interruptible b) {
synchronized (blockerLock) {
blocker = b;
}
}
blocker和blockerLock用于控制线程中断，blockedOn是给nio对blocker赋值用的
public final static int MIN_PRIORITY = 1; public final static int NORM_PRIORITY = 5; public final static int MAX_PRIORITY = 10;
线程的优先级常量
3、构造方法
public Thread() {
init(null, null, "Thread-" + nextThreadNum(), 0);
}
public Thread(Runnable target) {
init(null, target, "Thread-" + nextThreadNum(), 0);
}
Thread(Runnable target, AccessControlContext acc) {
init(null, target, "Thread-" + nextThreadNum(), 0, acc, false);
}
public Thread(ThreadGroup group, Runnable target) {
init(group, target, "Thread-" + nextThreadNum(), 0);
}
public Thread(String name) {
init(null, null, name, 0);
}
public Thread(ThreadGroup group, String name) {
init(group, null, name, 0);
}
public Thread(Runnable target, String name) {
init(null, target, name, 0);
}
public Thread(ThreadGroup group, Runnable target, String name) {
init(group, target, name, 0);
}
public Thread(ThreadGroup group, Runnable target, String name, long stackSize) {
init(group, target, name, stackSize);
}
各种构造方法
private void init(ThreadGroup g, Runnable target, String name,
long stackSize) {
init(g, target, name, stackSize, null, true);
}
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;
//从本地方法获得当前线程作为parent
Thread parent = currentThread();
//安全管理器相关
SecurityManager security = System.getSecurityManager();
if (g == null) {
if (security != null) {
g = security.getThreadGroup();
}
if (g == null) {
g = parent.getThreadGroup();
}
}
g.checkAccess();
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);
this.stackSize = stackSize;
tid = nextThreadID();
}
初始化线程的方法
4、一般方法
public static native Thread currentThread();
本地方法，获得当前线程
public static native void yield();
使线程暂停并允许执行其他线程
public static native void sleep(long millis) throws InterruptedException;
使线程睡眠指定的时间，单位毫秒
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);
}
使线程睡眠指定的时间，增加了一个纳秒，如果大于500微秒（500000纳秒），就增加1毫秒，是一个四舍五入的近似运算
@Override
protected Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException();
}
不支持克隆
public synchronized void start() {
if (threadStatus != 0)
throw new IllegalThreadStateException();
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();
启动线程，如果线程已经启动就不能启动了，如果启动失败就通知线程组启动失败
@Override
public void run() {
if (target != null) {
target.run();
}
}
执行线程
private void exit() {
if (group != null) {
group.threadTerminated(this);
group = null;
}
/* Aggressively null out all reference fields: see bug 4006245 */
target = null;
/* Speed the release of some of these resources */
threadLocals = null;
inheritableThreadLocals = null;
inheritedAccessControlContext = null;
blocker = null;
uncaughtExceptionHandler = null;
}
终止线程
public void interrupt() {
if (this != Thread.currentThread())
checkAccess();
synchronized (blockerLock) {
Interruptible b = blocker;
if (b != null) {
interrupt0(); // Just to set the interrupt flag
b.interrupt(this);
return;
}
}
interrupt0();
}
public static boolean interrupted() {
return currentThread().isInterrupted(true);
}
public boolean isInterrupted() {
return isInterrupted(false);
}
private native boolean isInterrupted(boolean ClearInterrupted);
中断线程，暂时还不理解，后面补充
public final native boolean isAlive();
本地方法，线程是否存活
public final void setPriority(int newPriority) {
ThreadGroup g;
checkAccess();
if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
throw new IllegalArgumentException();
}
if((g = getThreadGroup()) != null) {
if (newPriority > g.getMaxPriority()) {
newPriority = g.getMaxPriority();
}
setPriority0(priority = newPriority);
}
}
public final int getPriority() {
return priority;
}
设置优先级，获得优先级
public final synchronized void setName(String name) {
checkAccess();
if (name == null) {
throw new NullPointerException("name cannot be null");
}
this.name = name;
if (threadStatus != 0) {
setNativeName(name);
}
}
public final String getName() {
return name;
}
设置线程名称，获得线程名称
public final ThreadGroup getThreadGroup() {
return group;
}
获得线程组
public static int activeCount() {
return currentThread().getThreadGroup().activeCount();
}
线程组存活线程数
public static int enumerate(Thread tarray[]) {
return currentThread().getThreadGroup().enumerate(tarray);
}
将线程组的线程复制到数组中
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;
}
}
}
public final synchronized void join(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++;
}
join(millis);
}
public final void join() throws InterruptedException {
join(0);
}
等待当前线程结束，当线程不再存活时，再执行调用join方法的进程
public static void dumpStack() {
new Exception("Stack trace").printStackTrace();
}
打印输出流便于调试
public final void setDaemon(boolean on) {
checkAccess();
if (isAlive()) {
throw new IllegalThreadStateException();
}
daemon = on;
}
public final boolean isDaemon() {
return daemon;
}
设置为守护进程
public final void checkAccess() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkAccess(this);
}
}
安全验证，判断是否有权限修改此线程
public String toString() {
ThreadGroup group = getThreadGroup();
if (group != null) {
return "Thread[" + getName() + "," + getPriority() + "," +
group.getName() + "]";
} else {
return "Thread[" + getName() + "," + getPriority() + "," +
"" + "]";
}
}
输出tostring
public ClassLoader getContextClassLoader() {
if (contextClassLoader == null)
return null;
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
ClassLoader.checkClassLoaderPermission(contextClassLoader, Reflection.getCallerClass());
}
return contextClassLoader;
}
public void setContextClassLoader(ClassLoader cl) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
sm.checkPermission(new RuntimePermission("setContextClassLoader"));
}
contextClassLoader = cl;
}
获得和设置thread的类加载器
public static native boolean holdsLock(Object obj);
判断当前线程是否持有某个对象的锁
private static final StackTraceElement[] EMPTY_STACK_TRACE = new StackTraceElement[0];
public StackTraceElement[] getStackTrace() {
if (this != Thread.currentThread()) {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkPermission(
SecurityConstants.GET_STACK_TRACE_PERMISSION);
}
if (!isAlive()) {
return EMPTY_STACK_TRACE;
}
StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
StackTraceElement[] stackTrace = stackTraceArray[0];
if (stackTrace == null) {
stackTrace = EMPTY_STACK_TRACE;
}
return stackTrace;
} else {
return (new Exception()).getStackTrace();
}
}
private native static StackTraceElement[][] dumpThreads(Thread[] threads);
private native static Thread[] getThreads();
返回表示此线程的堆栈转储的堆栈跟踪元素数组
private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION = new RuntimePermission("enableContextClassLoaderOverride");
当enableContextClassLoaderOverride被开启时，checkPermission将被重写子类直接或间接地调用
private static class Caches {
static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits = new ConcurrentHashMap<>();
static final ReferenceQueue<Class<?>> subclassAuditsQueue = new ReferenceQueue<>();
}
subclassAudits保存子类的代码执行安全性检测结果，subclassAuditsQueue保存已审核过的子类弱引用
private static boolean isCCLOverridden(Class<?> cl) {
if (cl == Thread.class)
return false;
processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
Boolean result = Caches.subclassAudits.get(key);
if (result == null) {
result = Boolean.valueOf(auditSubclass(cl));
Caches.subclassAudits.putIfAbsent(key, result);
}
return result.booleanValue();
}
private static boolean auditSubclass(final Class<?> subcl) {
Boolean result = AccessController.doPrivileged(
new PrivilegedAction() {
public Boolean run() {
for (Class<?> cl = subcl;
cl != Thread.class;
cl = cl.getSuperclass())
{
try {
cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
return Boolean.TRUE;
} catch (NoSuchMethodException ex) {
}
try {
Class<?>[] params = {ClassLoader.class};
cl.getDeclaredMethod("setContextClassLoader", params);
return Boolean.TRUE;
} catch (NoSuchMethodException ex) {
}
}
return Boolean.FALSE;
}
}
);
return result.booleanValue();
}
static void processQueue(ReferenceQueue<Class<?>> queue, ConcurrentMap<? extends WeakReference<Class<?>>, ?> map)
{
Reference<? extends Class<?>> ref;
while((ref = queue.poll()) != null) {
map.remove(ref);
}
}
static class WeakClassKey extends WeakReference<Class<?>> {
private final int hash;
WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
super(cl, refQueue);
hash = System.identityHashCode(cl);
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
if (obj == this)
return true;
if (obj instanceof WeakClassKey) {
Object referent = get();
return (referent != null) && (referent == ((WeakClassKey) obj).get());
} else {
return false;
}
}
}
安全相关
public enum State {
NEW,
RUNNABLE,
BLOCKED,
WAITING,
TIMED_WAITING,
TERMINATED;
}
public State getState() {
return sun.misc.VM.toThreadState(threadStatus);
}
获得线程的状态
public interface UncaughtExceptionHandler {
void uncaughtException(Thread t, Throwable e);
}
private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
sm.checkPermission(new RuntimePermission("setDefaultUncaughtExceptionHandler"));
}
defaultUncaughtExceptionHandler = eh;
}
public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
return defaultUncaughtExceptionHandler;
}
public UncaughtExceptionHandler getUncaughtExceptionHandler() {
return uncaughtExceptionHandler != null ? uncaughtExceptionHandler : group;
}
public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
checkAccess();
uncaughtExceptionHandler = eh;
}
private void dispatchUncaughtException(Throwable e) {
getUncaughtExceptionHandler().uncaughtException(this, e);
}
异常处理相关，jvm会调用线程的getUncaughtExceptionHandler来处理未捕获的异常，这个异常实现Thread.UncaughtExceptionHandler接口，以下是ThreadGroup的实现
public void uncaughtException(Thread t, Throwable e) {
if (parent != null) {
parent.uncaughtException(t, e);
} else {
Thread.UncaughtExceptionHandler ueh = Thread.getDefaultUncaughtExceptionHandler();
if (ueh != null) {
ueh.uncaughtException(t, e);
} else if (!(e instanceof ThreadDeath)) {
System.err.print("Exception in thread \"" + t.getName() + "\" ");
e.printStackTrace(System.err);
}
}
}
优先调用当前线程的异常handler，没有的话调用全局的默认异常handler，如果还没有就执行e.printStackTrace
long threadLocalRandomSeed; int threadLocalRandomProbe; int threadLocalRandomSecondarySeed;
给ThreadLocalRandom使用的属性
private native void setPriority0(int newPriority); private native void stop0(Object o); private native void suspend0(); private native void resume0(); private native void interrupt0(); private native void setNativeName(String name);
一些私有的本地方法
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