前言:前一段時間在做項目的時候,某段代碼中用到了多線程,該處代碼需要開啓多個線程,待這幾個線程執行完畢後再接着執行後續的流程。現將可採用的方法記錄如下。
要達到上述的描述的情形,可以使用Thread的join()方法,也可以使用java.util.concurrent包中的CountDownLatch類。具體如下:
一、使用Thread.join()方法
該方法在JDK API中的解釋爲“等待該線程終止”,存在三個方法重載,如下:
void join();
void join(long millis); // 等待該線程終止的最長時間爲millis毫秒
void join(long millis, int nanos); // 等待該線程終止的最長時間爲millis毫秒+nanos納秒
代碼如下:
package threadTest;
import java.util.Vector;
import java.util.concurrent.*;
/**
* Created by worm0527 on 2017/7/17.
*/
public class ThreadTest extends Thread {
// 線程名稱
private String threadName;
// 線程休眠時間
private int sleepSec;
ThreadTest(String threadName, int sleepSec) {
super(threadName);
this.sleepSec = sleepSec;
start();// 在構造方法中啓動線程
}
@Override
public void run() {
long starttime = System.currentTimeMillis();
System.out.println(Thread.currentThread().getName() + " running...");
try {
// 休眠制定時間(單位:秒)
TimeUnit.SECONDS.sleep(sleepSec);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " run at " + (System.currentTimeMillis() - starttime) + " ms");
}
public static void main(String[] args) throws InterruptedException {
long starttime = System.currentTimeMillis();
System.out.println("Thread main running...");
Vector<Thread> threadVector = new Vector<Thread>();
for (int i = 1; i < 5; i++) { // 開啓四個線程
Thread t = new ThreadTest("Thread" + i, i);
threadVector.add(t);
}
for (Thread t : threadVector) { // 循環調用線程join()方法,等待線程結束
t.join();
}
System.out.println("Thread main End");
System.out.println("Thread main run at " + (System.currentTimeMillis() - starttime) + " ms");
}
}
運行結果:
二、使用CountDownLatch類
主要使用了該類的await()和countDown()兩個方法。await()阻塞線程,直到計數器歸零或者線程被中斷,調用countDown()來遞減計數器。
代碼如下:
package threadTest;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
/**
* Created by worm0527 on 2017/7/18.
*/
public class ThreadTest1 extends Thread {
// 線程名稱
private String threadName;
// 線程休眠時間
private int sleepSec;
private CountDownLatch latch; // 線程類中持有CountDownLatch對象的引用
public ThreadTest1(String threadName, int sleepSec, CountDownLatch latch) {
super(threadName);
this.sleepSec = sleepSec;
this.latch = latch;
start();// 在構造方法中啓動線程
}
@Override
public void run() {
long starttime = System.currentTimeMillis();
System.out.println(Thread.currentThread().getName() + " running...");
try {
// 休眠制定時間(單位:秒)
TimeUnit.SECONDS.sleep(sleepSec);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " run at " + (System.currentTimeMillis() - starttime) + " ms");
latch.countDown();
}
public static void main(String[] args) throws InterruptedException {
long starttime = System.currentTimeMillis();
System.out.println("Thread main running...");
CountDownLatch latch = new CountDownLatch(4); // 共四個子線程
for (int i = 1; i < 5; i++) {
new ThreadTest1("Thread" + i, i, latch);
}
latch.await(); // 阻塞,直到線程計數歸零
System.out.println("Thread main End");
System.out.println("Thread main run at " + (System.currentTimeMillis() - starttime) + " ms");
}
}
運行結果: