fairbridge.java

英国帝国理工学院电脑系多线程课程教学材料之十 ---- 单行道范例

package concurrency.bridge;

import java.awt.*;

class FairBridge extends Bridge {

    private int nred  = 0;
    private int nblue = 0;
    private int waitblue = 0;
    private int waitred = 0;
    private boolean blueturn = true;

    synchronized void redEnter() throws InterruptedException {
        ++waitred;
        while (nblue>0 || (waitblue>0 && blueturn)) wait();
        --waitred;
        ++nred;
    }

    synchronized void redExit(){
        --nred;
        blueturn = true;
        if (nred==0)
            notifyAll();
    }

    synchronized void blueEnter()  throws InterruptedException {
        ++waitblue;
        while (nred>0 || (waitred>0 && !blueturn)) wait();
        --waitblue;
        ++nblue;
    }

    synchronized void blueExit(){
        --nblue;
        blueturn = false;
        if (nblue==0)
            notifyAll();
    }
}