Java AsyncTask 分析内部实现

浏览数：28 / 时间：2015年06月08日

sdk3.0前，使用内部的线程池，多线程并发执行。线程池大小等于5，最大达128

sdk3.0后，使用默认的serial线程池，执行完一个线程，再顺序执行下一个线程。sdk4.3时线程池大小等于5，最大达128

sdk4.4后线程池大小等于 cpu count + 1，最大值为cpu count * 2 + 1

sdk3.0后有两种线程池的实现，默认为 Serial 线程池

[java] view plain copy print ?

public static final Executor SERIAL_EXECUTOR = new SerialExecutor();
public static final Executor THREAD_POOL_EXECUTOR
= new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);
private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
public static void setDefaultExecutor(Executor exec) {//设置默认线程池
sDefaultExecutor = exec;
}

SerialExecutor ，使用同步锁，一次执行一个线程

[java] view plain copy print ?

private static class SerialExecutor implements Executor {
final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
Runnable mActive;
public synchronized void execute(final Runnable r) {
mTasks.offer(new Runnable() {
public void run() {
try {
r.run();
} finally {
scheduleNext();
}
}
});
if (mActive == null) {
scheduleNext();
}
}
protected synchronized void scheduleNext() {
if ((mActive = mTasks.poll()) != null) {
THREAD_POOL_EXECUTOR.execute(mActive);
}
}
}
sdk3.0前，使用内部的线程池，多线程并发执行。线程池大小等于5，最大达128

sdk3.0后，使用默认的serial线程池，执行完一个线程，再顺序执行下一个线程。sdk4.3时线程池大小等于5，最大达128

sdk4.4后线程池大小等于 cpu count + 1，最大值为cpu count * 2 + 1

sdk3.0后有两种线程池的实现，默认为 Serial 线程池
[java] view plain copy print ?
1. public static final Executor SERIAL_EXECUTOR = new SerialExecutor();
2. public static final Executor THREAD_POOL_EXECUTOR
3. = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
4. TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);
5. private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
6. public static void setDefaultExecutor(Executor exec) {//设置默认线程池
7. sDefaultExecutor = exec;
8. }
SerialExecutor ，使用同步锁，一次执行一个线程
[java] view plain copy print ?
1. private static class SerialExecutor implements Executor {
2. final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
3. Runnable mActive;
5. public synchronized void execute(final Runnable r) {
6. mTasks.offer(new Runnable() {
7. public void run() {
8. try {
9. r.run();
10. } finally {
11. scheduleNext();
12. }
13. }
14. });
15. if (mActive == null) {
16. scheduleNext();
17. }
18. }
20. protected synchronized void scheduleNext() {
21. if ((mActive = mTasks.poll()) != null) {
22. THREAD_POOL_EXECUTOR.execute(mActive);
23. }
24. }
THREAD_POOL_EXECUTOR 并发线程池

asynctask.setDefaultExecutor(AsyncTask.THREAD_POOL_EXECUTOR); //设置使用并发线程池

asynctask.executeOnExecutor(executor); //可以自定义线程池使用这两种方法