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一、使用同一个共享变量控制
Synchronized、wait、notify
public class Demo1 { private final List<Integer> list =new ArrayList<>(); public static void main(String[] args) { Demo1 demo =new Demo1(); new Thread(()->{ for (int i=0;i<10;i++){ synchronized (demo.list){ if(demo.list.size()%2==1){ try { demo.list.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } demo.list.add(i); System.out.print(Thread.currentThread().getName()); System.out.println(demo.list); demo.list.notify(); } } }).start(); new Thread(()->{ for (int i=0;i<10;i++){ synchronized (demo.list){ if(demo.list.size()%2==0){ try { demo.list.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } demo.list.add(i); System.out.print(Thread.currentThread().getName()); System.out.println(demo.list); demo.list.notify(); } } }).start(); } }
欢迎大家来到IT世界,在知识的湖畔探索吧!
Lock、Condition
欢迎大家来到IT世界,在知识的湖畔探索吧!public class Task { private final Lock lock = new ReentrantLock(); private final Condition addConditon = lock.newCondition(); private final Condition subConditon = lock.newCondition(); private volatile int num = 0; private List<String> list = new ArrayList<>(); public void add() { for (int i = 0; i < 10; i++) { lock.lock(); try { if (list.size() == 10) { addConditon.await(); } num++; Thread.sleep(100); list.add("add " + num); System.out.println("The list size is " + list.size()); System.out.println("The add thread is " + Thread.currentThread().getName()); System.out.println("-------------"); subConditon.signal(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } } public void sub() { for (int i = 0; i < 10; i++) { lock.lock(); try { if (list.size() == 0) { subConditon.await(); } num--; Thread.sleep(100); list.remove(0); System.out.println("The list size is " + list.size()); System.out.println("The sub thread is " + Thread.currentThread().getName()); System.out.println("-------------"); addConditon.signal(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } } public static void main(String[] args) { Task task = new Task(); new Thread(task::add).start(); new Thread(task::sub).start(); } }
利用volatile
volatile修饰的变量值直接存在主内存里面,子线程对该变量的读写直接写住内存,而不是像其它变量一样在local thread里面产生一份copy。volatile能保证所修饰的变量对于多个线程可见性,即只要被修改,其它线程读到的一定是最新的值。
public class Demo2 { private volatile List<Integer> list =new ArrayList<>(); public static void main(String[] args) { Demo2 demo =new Demo2(); new Thread(()->{ for (int i=0;i<10;i++){ demo.list.add(i); System.out.print(Thread.currentThread().getName()); System.out.println(demo.list); } }).start(); new Thread(()->{ for (int i=0;i<10;i++){ demo.list.add(i); System.out.print(Thread.currentThread().getName()); System.out.println(demo.list); } }).start(); } }
利用AtomicInteger
和volatile类似
二、PipedInputStream、PipedOutputStream
这里用流在两个线程间通信,但是Java中的Stream是单向的,所以在两个线程中分别建了一个input和output
欢迎大家来到IT世界,在知识的湖畔探索吧!public class PipedDemo { private final PipedInputStream inputStream1; private final PipedOutputStream outputStream1; private final PipedInputStream inputStream2; private final PipedOutputStream outputStream2; public PipedDemo(){ inputStream1 = new PipedInputStream(); outputStream1 = new PipedOutputStream(); inputStream2 = new PipedInputStream(); outputStream2 = new PipedOutputStream(); try { inputStream1.connect(outputStream2); inputStream2.connect(outputStream1); } catch (IOException e) { e.printStackTrace(); } } /程序退出时,需要关闭stream*/ public void shutdown() throws IOException { inputStream1.close(); inputStream2.close(); outputStream1.close(); outputStream2.close(); } public static void main(String[] args) throws IOException { PipedDemo demo =new PipedDemo(); new Thread(()->{ PipedInputStream in = demo.inputStream2; PipedOutputStream out = demo.outputStream2; for (int i = 0; i < 10; i++) { try { byte[] inArr = new byte[2]; in.read(inArr); System.out.print(Thread.currentThread().getName()+": "+i+" "); System.out.println(new String(inArr)); while(true){ if("go".equals(new String(inArr))) break; } out.write("ok".getBytes()); } catch (IOException e) { e.printStackTrace(); } } }).start(); new Thread(()->{ PipedInputStream in = demo.inputStream1; PipedOutputStream out = demo.outputStream1; for (int i = 0; i < 10; i++) { try { out.write("go".getBytes()); byte[] inArr = new byte[2]; in.read(inArr); System.out.print(Thread.currentThread().getName()+": "+i+" "); System.out.println(new String(inArr)); while(true){ if("ok".equals(new String(inArr))) break; } } catch (IOException e) { e.printStackTrace(); } } }).start(); // demo.shutdown(); } }
输出
Thread-0: 0 go Thread-1: 0 ok Thread-0: 1 go Thread-1: 1 ok Thread-0: 2 go Thread-1: 2 ok Thread-0: 3 go Thread-1: 3 ok Thread-0: 4 go Thread-1: 4 ok Thread-0: 5 go Thread-1: 5 ok Thread-0: 6 go Thread-1: 6 ok Thread-0: 7 go Thread-1: 7 ok Thread-0: 8 go Thread-1: 8 ok Thread-0: 9 go Thread-1: 9 ok
三、利用BlockingQueue
BlockingQueue定义的常用方法如下:
- add(Object):把Object加到BlockingQueue里,如果BlockingQueue可以容纳,则返回true,否则抛出异常。
- offer(Object):表示如果可能的话,将Object加到BlockingQueue里,即如果BlockingQueue可以容纳,则返回true,否则返回false。
- put(Object):把Object加到BlockingQueue里,如果BlockingQueue没有空间,则调用此方法的线程被阻断直到BlockingQueue里有空间再继续。
- poll(time):获取并删除BlockingQueue里排在首位的对象,若不能立即取出,则可以等time参数规定的时间,取不到时返回null。当不传入time值时,立刻返回。
- peek():立刻获取BlockingQueue里排在首位的对象,但不从队列里删除,如果队列为空,则返回null。
- take():获取并删除BlockingQueue里排在首位的对象,若BlockingQueue为空,阻断进入等待状态直到BlockingQueue有新的对象被加入为止。
BlockingQueue有四个具体的实现类:
- ArrayBlockingQueue:数组阻塞队列,规定大小,其构造函数必须带一个int参数来指明其大小。其所含的对象是以FIFO(先入先出)顺序排序的。
- LinkedBlockingQueue:链阻塞队列,大小不定,若其构造函数带一个规定大小的参数,生成的BlockingQueue有大小限制,若不带大小参数,所生成的BlockingQueue的大小由Integer.MAX_VALUE来决定。其所含的对象是以FIFO顺序排序的。
- PriorityBlockingQueue:类似于LinkedBlockingQueue,但其所含对象的排序不是FIFO,而是依据对象的自然排序顺序或者是构造函数所带的Comparator决定的顺序。
- SynchronousQueue:特殊的BlockingQueue,它的内部同时只能够容纳单个元素,对其的操作必须是放和取交替完成的。
- DelayQueue:延迟队列,注入其中的元素必须实现 java.util.concurrent.Delayed 接口
所有BlockingQueue的使用方式类似,以下例子一个线程写入,一个线程读取,操作的是同一个Queue:
public class BlockingQueueDemo { public static void main(String[] args) { LinkedBlockingQueue<String> queue = new LinkedBlockingQueue<>(); //读线程 new Thread(() -> { int i =0; while (true) { try { String item = queue.take(); System.out.print(Thread.currentThread().getName() + ": " + i + " "); System.out.println(item); i++; } catch (Exception e) { e.printStackTrace(); } } }).start(); //写线程 new Thread(() -> { for (int i = 0; i < 10; i++) { try { String item = "go"+i; System.out.print(Thread.currentThread().getName() + ": " + i + " "); System.out.println(item); queue.put(item); } catch (Exception e) { e.printStackTrace(); } } }).start(); } }
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