安卓中使用ThreadPoolExcutor
- 原文链接 https://medium.freecodecamp.com/threadpoolexecutor-in-android-8e9d22330ee3#.hiw1y4s2e
- 翻译： Adamin90
- 转载请注明出处，谢谢！
这篇文章将涉及到线程池，线程池执行程序，和他们在Android中的使用。
我们将使用很多的利用，详细的（thoroughly）介绍这些主题。
Thread Pools (线程池)
一个线程池管理一池的工作线程（准确的数量依赖于它的实现方式）。
一个task队列等待池中的空闲线程执行队列中的task.Task被生产者加入队列中，工作线程作为消费者，只要池中有空闲线程在等待新的后台任务，就会从task队列中消费任务。
ThreadPoolExcutor
ThreadPoolExcutor 从线程池中的一个线程执行一个给定的task。
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue workQueue
);
参数解释：
- corePoolSize: 线程池中保留线程的最小数目，最开始线程池中没有线程，但是随着task被加入队列，新线程被创建。如果有空闲的线程，但是线程的数目小于corePoolSize，就会创建新的线程。
- maximumPoolSize: 线程池中线程的最大值，如果线程数量超过corePoolSize,线程数量>=corePoolSize,那么只有队列满的时候才会创建新的工作线程。
- keepAliveTime: 当线程数量超过corepoolsize，非corepoolsize的空闲线程将等待一个新的task，如果在这个定义的时间参数内没有等到新的task，该线程将被终止。
- unit： keppAliveTime的时间单位
- workQueue: task队列，持有runnable task，必须是一个BlockingQueue.
为什么在Android和JAVA应用程序中使用Thread Pool Executor?
- 它是一个强大的任务执行框架，支持任务添加到队列，任务取消，任务优先级。
- 降低了线程创建的开销，它在线程池内管理一定数量的线程。
在Android中使用ThreadPoolExcutor
首先，创建一个PriorityThreadFactory:
import android.os.Process;
import java.util.concurrent.ThreadFactory;
/**
* Created by Adam on 2016/7/29.
*/
public class PriorityThreadFactory implements ThreadFactory {
private final int mThreadPrority;
public PriorityThreadFactory(int mThreadPrority) {
this.mThreadPrority = mThreadPrority;
}
@Override
public Thread newThread(final Runnable r) {
Runnable runnable = new Runnable() {
@Override
public void run() {
try {
Process.setThreadPriority(mThreadPrority);
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
}
r.run();
;
}
};
return new Thread(runnable);
}
}
创建一个MainThreadExecutor:
import android.os.Handler;
import android.os.Looper;
import java.util.concurrent.Executor;
/**
* Created by Adam on 2016/7/29.
*/
public class MainThreadExecutor implements Executor {
private final Handler handler = new Handler(Looper.getMainLooper());
@Override
public void execute(Runnable command) {
handler.post(command);
}
}
创建一个DefaultExecutorSupplier:
import android.os.Process;
import java.util.concurrent.Executor;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
/**
* Created by Adam on 2016/7/29.
*/
public class DefaultExecutorSupplier {
/*
*指定线程数量
*/
public static final int NUMBER_OF_CORES = Runtime.getRuntime().availableProcessors();
/**
* 后台任务的线程池
*/
private final ThreadPoolExecutor mForBackgroundTasks;
/**
* 轻量后台任务的线程池
*/
private final ThreadPoolExecutor mForLightWeightBackgroundTasks;
/**
* 主线程任务的线程池executor
*/
private final Executor mMainThreadExcutor;
private static DefaultExecutorSupplier mInstance;
/**
* 返回DefaultExecutorSupplier的实例
*/
public static DefaultExecutorSupplier getInstance() {
if (mInstance == null) {
synchronized (DefaultExecutorSupplier.class) {
mInstance = new DefaultExecutorSupplier();
}
}
return mInstance;
}
private DefaultExecutorSupplier() {
ThreadFactory backgroundPriorityThreadFactory = new PriorityThreadFactory(Process.THREAD_PRIORITY_BACKGROUND);
mForBackgroundTasks = new ThreadPoolExecutor(
NUMBER_OF_CORES * 2,
NUMBER_OF_CORES * 2,
60L,
TimeUnit.SECONDS,
new LinkedBlockingQueue(),
backgroundPriorityThreadFactory
);
mForLightWeightBackgroundTasks = new ThreadPoolExecutor(
NUMBER_OF_CORES * 2,
NUMBER_OF_CORES * 2,
60L,
TimeUnit.SECONDS,
new LinkedBlockingQueue(),
backgroundPriorityThreadFactory
);
mMainThreadExcutor = new MainThreadExecutor();
}
/*
* returns the thread pool executor for background task
*/
public ThreadPoolExecutor forBackgroundTasks() {
return mForBackgroundTasks;
}
/*
* returns the thread pool executor for light weight background task
*/
public ThreadPoolExecutor forLightWeightBackgroundTasks() {
return mForLightWeightBackgroundTasks;
}
/*
* returns the thread pool executor for main thread task
*/
public Executor forMainThreadTasks() {
return mMainThreadExcutor;
}
}
注意：不同线程池的数量依赖于你的需求
现在在你的代码中这样使用
/*
* 后台任务
*/
public void doSomeBackgroundWork() {
DefaultExecutorSupplier.getInstance().forBackgroundTasks()
.execute(new Runnable() {
@Override
public void run() {
// 在这里后台工作.
}
});
}
/*
* 轻量后台任务
*/
public void doSomeLightWeightBackgroundWork() {
DefaultExecutorSupplier.getInstance().forLightWeightBackgroundTasks()
.execute(new Runnable() {
@Override
public void run() {
// 在这里做一些轻量后台工作.
}
});
}
/*
* 主线程任务
*/
public void doSomeMainThreadWork() {
DefaultExecutorSupplier.getInstance().forMainThreadTasks()
.execute(new Runnable() {
@Override
public void run() {
// 做一些中线程工作.
}
});
}
这样，我们可以为网络任务，I/O任务，重型的后台任务和其他任务创建不同的线程池。
怎样取消一个task？
为了取消一个task，你必须得到task的future。所以，不要使用execute，使用submit，将返回一个future。现在future就可以用来取消task了。
Future future= DefaultExecutorSupplier.getInstance().forBackgroundTasks()
.submit(new Runnable() {
@Override
public void run() {
}
});
future.cancel(true);
如何设置task的优先级？
假设队列里有20个任务，线程池持有4个线程，我们根据task的优先级处理他们，因为线程池此时同时可处理4个线程。
但是假设我们需要我们最后推进队列的任务最先执行，我们需要为该任务设置立即的优先当线程从队列里拿取新任务时。
为了设置任务的优先级，我们需要创建一个线程池executor。
为优先级创建一个枚举类:
/**
* Created by Adam on 2016/7/29.
*/
public enum Priority {
/**
* 注意：不要在任何情况下改变顺序，否则会使排序不准确
*/
/**
* 最低优先级，预加载数据用
*/
LOW,
/**
* 中优先级
*/
MEDIUM,
/**
* 高优先级
*/
HIGH,
/**
* 立即
*/
IMMEDIATE,
}
创建一个PriorityRunnable
public class PriorityRunnable implements Runnable {
private final Priority priority;
public PriorityRunnable(Priority priority) {
this.priority = priority;
}
@Override
public void run() {
}
public Priority getPriority(){
return priority;
}
}
创建一个PriorityThreadPoolExecutor,继承自ThreadPoolExecutor.我们必须创建PriorityFutureTask,将实现Comparable接口。
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;
import java.util.concurrent.PriorityBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
/**
* Created by Adam on 2016/7/29.
*/
public class PriorityThreadPoolExecutor extends ThreadPoolExecutor {
public PriorityThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue workQueue, ThreadFactory threadFactory) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, new PriorityBlockingQueue(), threadFactory);
}
@Override
public Future submit(Runnable task) {
PriorityFutureTask futureTask = new PriorityFutureTask((PriorityRunnable) task);
execute(futureTask);
return futureTask;
}
private static final class PriorityFutureTask extends FutureTask
implements Comparable {
private final PriorityRunnable priorityRunnable;
public PriorityFutureTask(PriorityRunnable priorityRunnable) {
super(priorityRunnable, null);
this.priorityRunnable = priorityRunnable;
}
@Override
public int compareTo(PriorityFutureTask another) {
Priority p1 = priorityRunnable.getPriority();
Priority p2 = another.priorityRunnable.getPriority();
return p2.ordinal() - p1.ordinal();
}
}
}
首先在DefaultExcutorSupplier,用PriorityThreadPoolExecutor代替ThreadPoolExecutor.
ThreadFactory backgroundPriorityThreadFactory = new PriorityThreadFactory(Process.THREAD_PRIORITY_BACKGROUND);
// mForBackgroundTasks = new ThreadPoolExecutor(
// NUMBER_OF_CORES * 2,
// NUMBER_OF_CORES * 2,
// 60L,
// TimeUnit.SECONDS,
// new LinkedBlockingQueue(),
// backgroundPriorityThreadFactory
//
// );
mForBackgroundTasks=new PriorityThreadPoolExecutor(
NUMBER_OF_CORES * 2,
NUMBER_OF_CORES * 2,
60L,
TimeUnit.SECONDS,
new LinkedBlockingQueue(),
backgroundPriorityThreadFactory
);
下面的例子演示了如何设置高优先级：
public void doSomeTaskAtHighPriority(){
DefaultExecutorSupplier.getInstance().forBackgroundTasks()
.submit(new PriorityRunnable(Priority.HIGH){
@Override
public void run() {
super.run();
}
});
}