多线程-Thread，Runnable，Callable，Future，RunnableFuture，FutureTask

Posted 2020-10-08 小路不懂2

类图：

 

先看各自的源码：

public interface Runnable {
    public abstract void run();
}

　　

public
class Thread implements Runnable {
    /* What will be run. */
    private Runnable target;
}

Thread与Runnable其实是一个装饰器模式。

public interface Callable<V> {
    V call() throws Exception;
}

　　

public interface Future<V> {
    boolean cancel(boolean mayInterruptIfRunning);
    boolean isCancelled();
    boolean isDone();
    V get() throws InterruptedException, ExecutionException;
    V get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;
}

　　

public interface RunnableFuture<V> extends Runnable, Future<V> {
    void run();
}

　　

public class FutureTask<V> implements RunnableFuture<V> {
 /** The underlying callable; nulled out after running */
    private Callable<V> callable;
 /** The result to return or exception to throw from get() */
    private Object outcome;
    public void run() {
        if (state != NEW ||
            !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                         null, Thread.currentThread()))
            return;
        try {
            Callable<V> c = callable;
            if (c != null && state == NEW) {
                V result;
                boolean ran;
                try {
                    result = c.call();
                    ran = true;
                } catch (Throwable ex) {
                    result = null;
                    ran = false;
                    setException(ex);
                }
                if (ran)
                    set(result);
            }
        } finally {
            // runner must be non-null until state is settled to
            // prevent concurrent calls to run()
            runner = null;
            // state must be re-read after nulling runner to prevent
            // leaked interrupts
            int s = state;
            if (s >= INTERRUPTING)
                handlePossibleCancellationInterrupt(s);
        }
    }
}

从类的结构来看： 
Runnable，Callable，Future接口本是互相独立的，没有直接的关系。 
而Thread的一系列构造函数需要的是Runnable对象，所以Callable对象并不适合Thread构造函数，而是借助于FutureTask这个类，该类实现具有Future和Runnable接口能力的类，同时组合Callable对象，FutureTask在run()方法中调用Callable的call()方法，这是个典型的适配器模式： 
Runable是个目标接口，定义了Thread所需的接口； 
Callable是被适配接口，定义了一个已经存在的接口方法call() 
FutureTask是个适配器类，作为一个转换器，将Runnable和Callable适配，适配器类是适配器模式的核心，它通过实现RunnableFuture和组合Callable使得两者产生关系。