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 1 package com.led.test; 2  3 /** 4  * @author Alan 5  * @date 2018/6/18 15:09 6  * @description 測(cè)試同一個(gè)線(xiàn)程多次調(diào)用start()方法 7  */ 8 public class MuchStart implements Runnable{ //實(shí)現(xiàn)Runnable接口 9     public void run() {10         System.out.println(Thread.currentThread().getName() + "is running ...");11     }12 13     public static void main(String[] args) {14         MuchStart muchStart = new MuchStart();15         Thread t = new Thread(muchStart);//創(chuàng)建實(shí)現(xiàn)了Runnable接口的Thread實(shí)例16         t.start();//多次調(diào)用start()方法17         t.start();18         t.start();19     }20 }

Thread-0is running ...Exception in thread "main" java.lang.IllegalThreadStateException    at java.lang.Thread.start(Thread.java:708)    at com.led.test.MuchStart.main(MuchStart.java:17)

 1 /** 2      * Causes this thread to begin execution; the Java Virtual Machine 3      * calls the <code>run</code> method of this thread.
　　　　  讓這個(gè)線(xiàn)程開(kāi)始執(zhí)行。JVM會(huì)調(diào)用這個(gè)線(xiàn)程的run()方法。 4      * <p> 5      * The result is that two threads are running concurrently: the 6      * current thread (which returns from the call to the 7      * <code>start</code> method) and the other thread (which executes its 8      * <code>run</code> method). 9      * <p>10      * It is never legal to start a thread more than once.一個(gè)線(xiàn)程多次調(diào)用start()方法是非法的。11      * In particular, a thread may not be restarted once it has completed12      * execution.13      *特別說(shuō)明：一個(gè)線(xiàn)程執(zhí)行完后，不太可能重新運(yùn)行。14      * @exception  IllegalThreadStateException  if the thread was already15      *               started.
　　　　　　　　　　　　　　如果該線(xiàn)程已經(jīng)啟動(dòng)，則再次調(diào)用start()方法，就會(huì)拋出IllegalThreadStateException異常。16      * @see        #run()17      * @see        #stop()18      */19     public synchronized void start() {20         /**21          * This method is not invoked for the main method thread or "system"22          * group threads created/set up by the VM. Any new functionality added23          * to this method in the future may have to also be added to the VM.24          *25          * A zero status value corresponds to state "NEW".26          */27         if (threadStatus != 0)//新的線(xiàn)程threadState值是028             throw new IllegalThreadStateException();29 30         /* Notify the group that this thread is about to be started31          * so that it can be added to the group's list of threads32          * and the group's unstarted count can be decremented. */33         group.add(this);//通知線(xiàn)程組該線(xiàn)程將要開(kāi)始運(yùn)行，這樣該線(xiàn)程就會(huì)被添加到線(xiàn)程列表中，此時(shí)列表的unstarted數(shù)將會(huì)減少。34 35         boolean started = false;36         try {37             start0();//調(diào)用原生方法態(tài)方法啟動(dòng)線(xiàn)程38             started = true;//已經(jīng)運(yùn)行的標(biāo)記設(shè)置為true39         } finally {40             try {41                 if (!started) {//若開(kāi)始運(yùn)行標(biāo)記未設(shè)置成功，則通知線(xiàn)程組該線(xiàn)程嘗試運(yùn)行失敗42                     group.threadStartFailed(this);43                 }44             } catch (Throwable ignore) {45                 /* do nothing. If start0 threw a Throwable then46                   it will be passed up the call stack */47             }48         }49     }

 1 /** 2      * Adds the specified thread to this thread group. 3      * 添加特定的線(xiàn)程到該線(xiàn)程組 4      * <p> Note: This method is called from both library code 5      * and the Virtual Machine. It is called from VM to add 6      * certain system threads to the system thread group. 7      * 8      * @param  t 9      *         the Thread to be added10      *11      * @throws  IllegalThreadStateException12      *          if the Thread group has been destroyed13      */14     void add(Thread t) {15         synchronized (this) {//線(xiàn)程同步16             if (destroyed) {//如果線(xiàn)程組的銷(xiāo)毀標(biāo)記(destroyed)是true，則拋出IllegalThreadStateException17                 throw new IllegalThreadStateException();18             }19             if (threads == null) {//如果線(xiàn)程數(shù)組為空，則初始為4個(gè)新的線(xiàn)程20                 threads = new Thread[4];21             } else if (nthreads == threads.length) {//如果當(dāng)前線(xiàn)程組已滿(mǎn)，則擴(kuò)容至原來(lái)的2倍22                 threads = Arrays.copyOf(threads, nthreads * 2);23             }24             threads[nthreads] = t;//將當(dāng)前線(xiàn)程放入線(xiàn)程數(shù)組的末尾25 26             // This is done last so it doesn't matter in case the27             // thread is killed28             nthreads++;//線(xiàn)程數(shù)組元素個(gè)數(shù)+129 30             // The thread is now a fully fledged member of the group, even31             // though it may, or may not, have been started yet. It will prevent32             // the group from being destroyed so the unstarted Threads count is33             // decremented.34             nUnstartedThreads--;//未啟動(dòng)線(xiàn)程數(shù)-135         }36     }

1 private native void start0();//原生態(tài)代碼，源碼不在當(dāng)前文件中，調(diào)用的其它文件的代碼（可能是c/c++寫(xiě)的代碼）

 1 /** 2      * Notifies the group that the thread {@code t} has failed 3      * an attempt to start. 4      * 通知線(xiàn)程組該線(xiàn)程嘗試運(yùn)行失敗 5      * <p> The state of this thread group is rolled back as if the 6      * attempt to start the thread has never occurred. The thread is again 7      * considered an unstarted member of the thread group, and a subsequent 8      * attempt to start the thread is permitted. 9      *10      * @param  t11      *         the Thread whose start method was invoked12      */13     void threadStartFailed(Thread t) {14         synchronized(this) {//同步15             remove(t);//從線(xiàn)程組中移除該線(xiàn)程16             nUnstartedThreads++;//未啟動(dòng)線(xiàn)程數(shù)+117         }18     }