我们先来分别看一下这两个接口
Runnable:
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
// package java.lang; @FunctionalInterface
public interface Runnable {
void run();
}
只有一个方法run(),表示执行任务的逻辑。
Callable:
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
// package java.util.concurrent; @FunctionalInterface
public interface Callable<V> {
V call() throws Exception;
}
也只有一个方法call(),但是是一个有返回值的方法，这给我们提供了获取方法执行结果的可能，即使它是个异步的任务，它可以获取异常，给我们极大地便利知道任务执行失败的原因。
Runnable例子Demo:
package cn.concurrent.executor; /**
* Created by spark on 17-9-24.
*/
public class RunnabelDemo implements Runnable { public RunnabelDemo(String acceptStr) {
this.acceptStr = acceptStr;
} private String acceptStr; @Override
public void run() {
try {
// 线程阻塞 1 秒，此时有异常产生，只能在方法内部消化，无法上抛
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// 最终处理结果无法返回
System.out.println("hello : " + this.acceptStr);
} public static void main(String[] args) {
Runnable runnable = new RunnabelDemo("my runable test!");
long beginTime = System.currentTimeMillis();
new Thread(runnable).start();
long endTime = System.currentTimeMillis();
System.out.println("cast : " + (endTime - beginTime) / 1000 + " second!");
}
}
结果：
/usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=41745:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.RunnabelDemo
cast : 0 second!
hello : my runable test! Process finished with exit code 0
Callable的例子:
package cn.concurrent.executor; import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask; /**
* Created by spark on 17-9-24.
*/
public class CallableDemo implements Callable<String> { private String name; public CallableDemo(String name) {
this.name = name;
} @Override
public String call() throws Exception {
//执行任务的相关逻辑
Thread.sleep(1000);
return name + " : this is task is successed.";
} public static void main(String[] args) throws ExecutionException, InterruptedException {
CallableDemo callableDemo = new CallableDemo("wade");
//异步执行的结果
FutureTask<String> future = new FutureTask<String>(callableDemo);
new Thread(future).start();
//調用get()方法--阻塞
String result=future.get();
System.out.println("hello : " + result);
}
}
结果:
/usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=37879:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.CallableDemo
hello : wade : this is task is successed. Process finished with exit code 0
问题:如何把一个Runnbale的任务转变为有返回值的Callable的任务。
^_^我们有工具类Executors可以帮我们实现,如下图：
其中Executors.callable(Runnable),就是我们需要的方法，是不是很简单呢。
代码如下:
package cn.concurrent.executor; import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask; /**
* Created by spark on 17-9-24.
*/
public class RunnableToCallable implements Runnable { String name; public RunnableToCallable(String name) {
this.name = name;
} @Override
public void run() {
try {
Thread.sleep(1000);
System.out.println(name + " :任务执行完毕！");
} catch (InterruptedException e) {
e.printStackTrace();
}
} public static void main(String[] args) throws ExecutionException, InterruptedException {
RunnableToCallable task=new RunnableToCallable("wade");
//转变为有返回值的任务
Callable<Object> future=Executors.callable(task);
FutureTask<Object> futureTask=new FutureTask<Object>(future);
new Thread(futureTask).start();
//調用get()方法--阻塞
Object result=futureTask.get();
System.out.println("hello : " + result);
}
}
结果如下：
/usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=36136:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.RunnableToCallable
wade :任务执行完毕！
hello : null Process finished with exit code 0
说明:因为该任务没有返回结果，因此返回的为null.
接下来我们讨论一下ExecutorService.executr()与ExecutorService.submit()方法的区别。
类图如下：
从类图可以看到：
execute只能接受Runnable类型的任务，并且没有返回值。
submit不管是Runnable还是Callable类型的任务都可以接受，但是Runnable返回值均为void，所以使用Future的get()获得的还是null
然后来看异常处理：
对于Runnable 只能通过try-catch来捕获异常，对于Callable,直接抛出就可以，然后在get的时候捕获异常进行处理。
如下：
package cn.concurrent.executor; import java.util.concurrent.*; /**
* Created by spark on 17-9-24.
*/
public class ThreadExceptionTest { public static void main(String[] args) {
ExecutorService executorService = Executors.newCachedThreadPool();
CallableTest callableTest = new CallableTest();
Future<Boolean> task = executorService.submit(callableTest);
try {
Boolean b = task.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
} } static class CallableTest implements Callable<Boolean> { @Override
public Boolean call() throws Exception {
int num = 3 / 0;
return false;
}
}
}
结果：
/usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=42960:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.ThreadExceptionTest
java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at cn.concurrent.executor.ThreadExceptionTest.main(ThreadExceptionTest.java:16)
Caused by: java.lang.ArithmeticException: / by zero
at cn.concurrent.executor.ThreadExceptionTest$CallableTest.call(ThreadExceptionTest.java:29)
at cn.concurrent.executor.ThreadExceptionTest$CallableTest.call(ThreadExceptionTest.java:25)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748) Process finished with exit code 0
get()方法会捕获异常。
接下来，我们详细了解一下Future接口，实现类FutureTask(它有三种状态，分别为未启动，已启动，已完成);
类图如下：
1.首先可以看到，它也是一个线程，可以直接继承它来运行任务，然后交给ExecutorService执行。
如下：
package cn.concurrent.executor; import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask; /**
* Created by spark on 17-9-24.
*/
public class FutureTaskDemo extends FutureTask<String> {
public FutureTaskDemo(Runnable runnable, String s) {
super(runnable, s);
System.out.println(s);
} @Override
public void run() {
try {
Thread.sleep(1000);
System.out.println("this is running.");
} catch (InterruptedException e) {
e.printStackTrace();
}
} public static void main(String[] args) {
FutureTaskDemo futureTaskDemo = new FutureTaskDemo(new Runnable() {
@Override
public void run() {
System.out.println("this is wade.");
}
}, "wade"); ExecutorService es = Executors.newFixedThreadPool(1);
FutureTask<String> task = (FutureTask<String>) es.submit(futureTaskDemo);
System.out.println("hello:"+task);
es.shutdown();
}
}
结果如下：
/usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=46018:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.FutureTaskDemo
wade
hello:java.util.concurrent.FutureTask@266474c2
this is running. Process finished with exit code 0
2.看一下run()方法
public void run() {
/**
*首先判断任务的状态 如果任务的状态不是new 说明任务的状态已经改变（说明他已经走了4种可能变化的一种）
* 如果状态是new就会把 当前执行任务的线程付给runner, 这里用的cmpandset如果runner不为空 说明已经有线程在执行
* 任务也会退出执行,如果状态是new并且runner为空并且把当前的线程付给了runner那么就继续执行任务(runner state 都是 volatile
*类型的变量是一个很轻量机的线程安全操作)
*引起state状态变化的原因 就是调用了cancel 或是 run
**/
if (state != NEW ||
!UNSAFE.compareAndSwapObject(this, runnerOffset,
null, Thread.currentThread()))
return;
//开始执行任务
try {
Callable<V> c = callable;
/**
* 如果 要执行的任务不为空 并且状态 new 就执行
***/
if (c != null && state == NEW) {
V result;
boolean ran;
try {
//执行任务
result = c.call();
//如果没有意外发生就执行成功了
ran = true;
} catch (Throwable ex) {
//有异常
result = null;
ran = false;
//设置异常
setException(ex);
}
//如果转型成功了 设置结果
if (ran)
(result);
}
} finally {
// runner must be non-null until state is settled to
// prevent concurrent calls to run()
//不管是否执行成功了 都把runner设置成null
runner = null;
// state must be re-read after nulling runner to prevent
// leaked interrupts
int s = state;
if (s >= INTERRUPTING)
handlePossibleCancellationInterrupt(s);
}
}
Task执行后如果成功会调用set()方法,如果有异常会调用setException()方法。
我们先看下set方法 ：
protected void set(V v) {
/**
*如过state是new 把state设置成 COMPLETING
*
**/
if (UNSAFE.compareAndSwapInt(this, stateOffset, NEW, COMPLETING)) {
outcome = v;
//将任务设置成NORMAL over the task
UNSAFE.putOrderedInt(this, stateOffset, NORMAL); // final state
finishCompletion();
}
}
最后，来看一下最重要的方法get();
public V get() throws InterruptedException, ExecutionException {
int s = state;
//当线程状态为新建活着执行中时一直调用awaitDone方法
if (s <= COMPLETING)
//循环判断线程状态是否已经执行成功，如果执行成功返回线程状态；其中还包括线程取消，中断等情况的判断。可参见下方源码。
//所以这里便是上面例子中为什么线程执行成功后即可立即得到结果，如果还没有执行成功
s = awaitDone(false, 0L);
//线程状态正常返回结果
return report(s);
}
如果get时,FutureTask的状态为未完成状态，则调用awaitDone方法进行阻塞。awaitDone():
private int awaitDone(boolean timed, long nanos)
throws InterruptedException {
//计算一下需要等待的时间，有可能为0，为0的话就无限期等待。
final long deadline = timed ? System.nanoTime() + nanos : 0L;
//一个等待节点
WaitNode q = null;
//是否加入队列
boolean queued = false;
for (;;) {
//如果当且调用get方法的线程被interrupt 那么就把当前线程从等待队列remove
//然后抛出异常
if (Thread.interrupted()) {
removeWaiter(q);
throw new InterruptedException();
}
int s = state;
//如果任务已经完成 不管是被暂停了 还是出现异常了 只要状态大于COMPLETING就返回。
if (s > COMPLETING) {
if (q != null)
q.thread = null;
return s;
}
else if (s == COMPLETING) // cannot time out yet
//如果任务正在完成中(注意是ING进行时) 那么让出一会CPU时间在继续执行
Thread.yield();
else if (q == null)
//创建等待节点
q = new WaitNode();
else if (!queued)
//第一次创建的等待节点需要加入等待队列，这里加入队列等待。
queued = UNSAFE.compareAndSwapObject(this, waitersOffset,
q.next = waiters, q);
else if (timed) {
//如果设置了等待 那么就得锁住线程等待，如果时间到了就返回状态。
//方法 public V get(long timeout, TimeUnit unit) 这里会根据状态做后续处理。
nanos = deadline - System.nanoTime();
if (nanos <= 0L) {
removeWaiter(q);
return state;
}
LockSupport.parkNanos(this, nanos);
}
else
//否则锁住线程等待其他线程解锁。
LockSupport.park(this);
}
}
awaitDone方法可以看成是不断轮询查看FutureTask的状态。在get阻塞期间：
如果执行get的线程被中断，则移除FutureTask的所有阻塞队列中的线程（waiters）,并抛出中断异常；
如果FutureTask的状态转换为完成状态（正常完成或取消），则返回完成状态；
如果FutureTask的状态变为COMPLETING, 则说明正在set结果，此时让线程等一等；
如果FutureTask的状态为初始态NEW，则将当前线程加入到FutureTask的阻塞线程中去；
如果get方法没有设置超时时间，则阻塞当前调用get线程；如果设置了超时时间，则判断是否达到超时时间，如果到达，则移除FutureTask的所有阻塞列队中的线程，并返回此时FutureTask的状态，如果未到达时间，则在剩下的时间内继续阻塞当前线程。
详细了解这几个方法：
当FutureTask处于未启动或者已启动状态时，执行Future.get()方法，将导致调用线程阻塞，当FutureTask处于已完成状态时，执行Future.get()方法时，将调用线程立即返回结果或者抛出异常。
当FutureTask处于未启动状态时，执行Future.cancel()方法,导致此任务永远不会被执行 ；当FutureTask处于已启动状态时，执行Future.cancel()方法将以中断执行此任务线程的方式来试图停止任务;当FutureTask处于已启动状态时，执行Future.cancel(false)方法不会对正在执行此任务的线程产生影响。
说明：Future.get()方法的实现基于AbstractQueuedSynchronizer(简称为AQS)，并发包中有很多可阻塞类(如ReentrantLock)都是基于AQS实现的，AQS是一个同步框架，它提供了通用机制来原子性管理同步状态，阻塞和唤醒线程，以及维护被阻塞线程的队列，后面有专门博客介绍AQS.
博客有很多的不足，望大家指点。