JAVA线程的一些总结

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1.避免过多的同步

// Page 196import java.util.*;public abstract class WorkQueue {    private final List queue = new LinkedList();    private boolean stopped = false;    protected WorkQueue() { new WorkerThread().start(); }    public final void enqueue(Object workItem) {        synchronized (queue) {            queue.add(workItem);            queue.notify();        }    }    public final void stop()  {        synchronized (queue) {            stopped = true;            queue.notify();        }    }    protected abstract void processItem(Object workItem)        throws InterruptedException;    // Broken - invokes alien method from synchronized block!    private class WorkerThread extends Thread {        public void run() {            while (true) {  // Main loop                synchronized (queue) {                    try {                        while (queue.isEmpty() && !stopped)                            queue.wait();                    } catch (InterruptedException e) {                        return;                    }                    if (stopped)                        return;                    Object workItem = queue.remove(0);                    try {                        processItem(workItem); // Lock held!                    } catch (InterruptedException e) {                        return;                    }                }            }        }    }/* COMMENTED OUT    // Alien method outside synchronized block - "Open call" - Page 198    private class WorkerThread extends Thread {        public void run() {            while (true) {  // Main loop                Object workItem = null;                synchronized (queue) {                    try {                        while (queue.isEmpty() && !stopped)                            queue.wait();                    } catch (InterruptedException e) {                        return;                    }                    if (stopped)                        return;                    workItem = queue.remove(0);                }                try {                    processItem(workItem); // No lock held                } catch (InterruptedException e) {                    return;                }            }        }    }*/}// Page 198class DeadlockQueue extends WorkQueue {    protected void processItem(final Object workItem)            throws InterruptedException {        // Create a new thread that returns workItem to queue        Thread child = new Thread() {            public void run() { enqueue(workItem); }        };        child.start();        child.join(); // Deadlock!        // Will never print (unless open call version of WorkerThread is used        System.out.println(workItem);    }    public static void main(String[] args) throws InterruptedException {        WorkQueue queue = new DeadlockQueue();        for (int i = 0; i < args.length; i++)            queue.enqueue(args[i]);        // Let items print for a while and then stop the queue        Thread.sleep(1000);        queue.stop();    }}

以上代码就出现了A释放锁需要等B执行完，但是B需要A的锁才能执行完毕。这样就出现了死锁。

解决方案就是把processItem拿到同步的外面来。

2.尽量不要依赖线程的调度，比如yield

3.不要使用线程组

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