12.2 排他(mutual exclusion)制御

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12.2 排他(mutual exclusion)制御

独立の並行して走るスレッドから同じオブジェクトをアクセスするプログラムコードは きわどい領域(critical sections)と呼ばれる．


// synchronize1.java
class synchronize1
{
    public static void main(String args[])
    {
        Shared shared = new Shared();

        CustomThread4 thread1 =
            new CustomThread4(shared, "one");
        CustomThread4 thread2 =
            new CustomThread4(shared, "two");
        CustomThread4 thread3 =
            new CustomThread4(shared, "three");
        CustomThread4 thread4 =
            new CustomThread4(shared, "four");

        try {
            thread1.join();
            thread2.join();
            thread3.join();
            thread4.join();
        } catch(InterruptedException e) {}
    }
}

class CustomThread4 extends Thread
{
    Shared shared;

    public
      CustomThread4(Shared shared, String string)
    {
        super(string);
        this.shared = shared;
        start();
    }

    public void run() {
        shared.doWork(
            Thread.currentThread().getName());
    }
}

class Shared
{
    void doWork(String string)
    {
        System.out.println("Starting " + string);
        try {
            Thread.sleep((long)
                         (Math.random() * 500));
        } catch (InterruptedException e) {}
        
        System.out.println("Ending " + string);
    }
}


これを実行すると，

% java synchronize1
Starting one
Starting two
Starting three
Starting four
Ending one
Ending two
Ending four
Ending three

という形で，Endingの順番がStartingの順番と異なる．

generated through LaTeX2HTML. M.Inaba 平成18年5月7日