一定要满足的条件 Guard Condition ,警戒条件。
public class Request { private final String name; public Request(String name) { this.name = name; } public String getName() { return name; } public String toString() { return "[ Request " + name + " ]"; } }
public class RequestQueue { private final LinkedList queue = new LinkedList(); public synchronized Request getRequest() { while (queue.size() <= 0) { try { wait(); } catch (InterruptedException e) { } } return (Request)queue.removeFirst(); } public synchronized void putRequest(Request request) { queue.addLast(request); notifyAll(); } }
public class ClientThread extends Thread { private Random random; private RequestQueue requestQueue; public ClientThread(RequestQueue requestQueue, String name, long seed) { super(name); this.requestQueue = requestQueue; this.random = new Random(seed); } public void run() { for (int i = 0; i < 10000; i++) { Request request = new Request("No." + i); System.out.println(Thread.currentThread().getName() + " requests " + request); requestQueue.putRequest(request); try { Thread.sleep(random.nextInt(1000)); } catch (InterruptedException e) { } } } }
public class ServerThread extends Thread { private Random random; private RequestQueue requestQueue; public ServerThread(RequestQueue requestQueue, String name, long seed) { super(name); this.requestQueue = requestQueue; this.random = new Random(seed); } public void run() { for (int i = 0; i < 10000; i++) { Request request = requestQueue.getRequest(); System.out.println(Thread.currentThread().getName() + " handles " + request); try { Thread.sleep(random.nextInt(1000)); } catch (InterruptedException e) { } } } }
public class Main { public static void main(String[] args) { RequestQueue requestQueue = new RequestQueue(); new ClientThread(requestQueue, "Alice", 3141592L).start(); new ServerThread(requestQueue, "Bobby", 6535897L).start(); } }
理解为 带条件的同步关键字。 wait / notify
1、while(!ready){ wait(); } ready = true; notifyAll(); 2、while(!ready){ Thread.yield(); } ready=true;
注:Thread.yield(); 不会解除锁定,所以这句不应该放在同步关键字中。 ready 声明为 volatile