首頁猿問 java多線程關(guān)于join 的問題

java多線程關(guān)于join 的問題

Java

呼啦一陣風(fēng) 2019-02-19 16:05:09

我想通過join讓線程 a b c d順序打印，但是現(xiàn)在是亂序打印 public class ExJoin extends Thread { Thread thread; public ExJoin(){ } public ExJoin(Thread thread){ this.thread = thread; } @Override public void run() { try { if (thread != null){ thread.join(); } System.out.println(Thread.currentThread().getName()+" is running"); } catch (InterruptedException e) { e.printStackTrace(); } } public static void main(String[] args) { Thread threadA = new ExJoin(); threadA.setName("A"); Thread threadB = new ExJoin(threadA); threadB.setName("B"); Thread threadC = new ExJoin(threadB); threadC.setName("C"); Thread threadD = new ExJoin(threadC); threadD.setName("D"); threadC.start(); threadD.start(); threadA.start(); threadB.start(); } }

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3 回答

HUX布斯

TA貢獻1876條經(jīng)驗獲得超6個贊

按照樓主的代碼邏輯，join是無法做到有序的，因為A/B/C/D線程的啟動運行依賴于CPU調(diào)度，如果線程B未啟動線程C調(diào)用threadB.join方法是不會生效的?？梢钥纯?code>jdk內(nèi)置的邏輯實現(xiàn)isAlive()為false時直接返回了。

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;
        }
    }
}

反對回復(fù) 2019-03-01