java線程的狀態

時間 2019-11-26

標籤 java 線程狀態欄目 Java 简体版

原文原文鏈接

線程狀態

線程的狀態包含，NEW，RUNNABLE，BLOCKED，WAITING，TIMED_WAITING，TERMINATED

線程狀態相關定義由java.lang.Thread.State枚舉給出
/**
 * Thread state for a thread which has not yet started.
 */
NEW, 

/**
 * Thread state for a runnable thread.  A thread in the runnable
 * state is executing in the Java virtual machine but it may
 * be waiting for other resources from the operating system
 * such as processor.
 */
RUNNABLE, 

/**
 * Thread state for a thread blocked waiting for a monitor lock.
 * A thread in the blocked state is waiting for a monitor lock
 * to enter a synchronized block/method or
 * reenter a synchronized block/method after calling
 * {@link Object#wait() Object.wait}.
 */
BLOCKED,

/**
 * Thread state for a waiting thread.
 * A thread is in the waiting state due to calling one of the
 * following methods:
 * <ul>
 *   <li>{@link Object#wait() Object.wait} with no timeout</li>
 *   <li>{@link #join() Thread.join} with no timeout</li>
 *   <li>{@link LockSupport#park() LockSupport.park}</li>
 * </ul>
 *
 * <p>A thread in the waiting state is waiting for another thread to
 * perform a particular action.
 *
 * For example, a thread that has called <tt>Object.wait()</tt>
 * on an object is waiting for another thread to call
 * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
 * that object. A thread that has called <tt>Thread.join()</tt>
 * is waiting for a specified thread to terminate.
 */
WAITING,

/**
 * Thread state for a waiting thread with a specified waiting time.
 * A thread is in the timed waiting state due to calling one of
 * the following methods with a specified positive waiting time:
 * <ul>
 *   <li>{@link #sleep Thread.sleep}</li>
 *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
 *   <li>{@link #join(long) Thread.join} with timeout</li>
 *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
 *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
 * </ul>
 */
TIMED_WAITING,

/**
 * Thread state for a terminated thread.
 * The thread has completed execution.
 */
TERMINATED;

具體事例場景

NEW

private static void testThreadNew() {
    Thread thread = new Thread();
    System.out.println(thread.getState());
}
Console:NEW
當線程被建立且不作其餘操做時爲NEW

RUNNABLE

private static void testThreadRunnable() {
    Thread thread = new Thread();
    thread.start();
    System.out.println(thread.getState());
}
當前線程被建立且.start時線程進入Runnable狀態

BLOCKED

private static final Object lockObj = new Object();
private static void testThreadBlocked() throws InterruptedException {
    Thread thread1 = new Thread(new TestBkickedRunnable());
    thread1.setName("線程1");
    thread1.start();
    //主線程阻塞，使得線程1 同步住
    Thread.sleep(1000L);
    Thread thread2 = new Thread(new TestBkickedRunnable());
    thread2.setName("線程2");
    thread2.start();
    Thread.sleep(Integer.MAX_VALUE);
}


static class TestBkickedRunnable implements Runnable {
    @Override
    public void run() {
        synchronized(lockObj) {
            try {
                //sleep會持有鎖，wait不會
                Thread.sleep(Integer.MAX_VALUE);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}
線程等待監視鎖阻塞的線程狀態。
處於阻塞狀態的線程正在等待監視器鎖。
當線程1使用同步塊或方法獲取對象監視鎖後未釋放，線程2想獲取監視鎖這個監視鎖時，線程2從新進入同步塊/方法調用後會進入blocking狀態。
查看方式
1.使用 jps -m 獲取到pid
2. 使用stack pid 查看 關注設置的制指定名稱的線程狀態

注意block狀態只針對於synchronized有效，當使用java.util.concurrent.lock時沒有這個狀態java

WAIT

private static final Object lockObj = new Object();

private static void testThreadWait() {
    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                synchronized (lockObj) {
                    lockObj.wait();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    });
    thread.setName("等待線程");
    thread.start();
}
線程調用wait,join,LockSupport.park方法進入等待狀態
當被調用notify,notifyAll,LockSupport.unpark時解除

TIMED_WAITING

private static final Object lockObj = new Object();

private static void testThreadWaitTimed() {
    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                synchronized (lockObj) {
                    lockObj.wait(1000000L);
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    });
    thread.setName("等待超時線程");
    thread.start();
}
線程調用wait(time),join(join),LockSupport.parkNanos，LockSupport.parkUntil方法進入等待狀態
達到指定時間時解除

TERMINATED

private static void testThreadTerminated() throws InterruptedException {
    Thread thread = new Thread();
    thread.setName("結束線程");
    thread.start();
    //給線程執行時間
    Thread.sleep(200L);
    System.out.println(thread.getState()); TERMINATED
    Thread.sleep(Integer.MAX_VALUE);
}
線程執行完畢後進入狀態