public AsyncTask() {
//[1]
mWorker = new WorkerRunnable<Params, Result>() {
public Result call() throws Exception {
mTaskInvoked.set(true);
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
return postResult(doInBackground(mParams));//doInBackground(mParams)對外使用
}
};
//[2]
mFuture = new FutureTask<Result>(mWorker) {
@Override
protected void done() {
try {
postResultIfNotInvoked(get());
} catch (InterruptedException e) {
android.util.Log.w(LOG_TAG, e);
} catch (ExecutionException e) {
throw new RuntimeException("An error occured while executing doInBackground()",
e.getCause());
} catch (CancellationException e) {
postResultIfNotInvoked(null);
}
}
};
}
[1]
其中WorkerRunnable
@FunctionalInterface
public interface Callable<V> {
V call() throws Exception;
}
private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
Params[] mParams;
}
將doInBackground的結果返回到postResult方法中
private Result postResult(Result result) {
@SuppressWarnings("unchecked")
Message message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
new AsyncTaskResult<Result>(this, result));
message.sendToTarget();
return result;
}
其中sHandler是InternalHandler的實例
private static class InternalHandler extends Handler {
@SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
@Override
public void handleMessage(Message msg) {
AsyncTaskResult result = (AsyncTaskResult) msg.obj;
switch (msg.what) {
case MESSAGE_POST_RESULT:
// There is only one result
result.mTask.finish(result.mData[0]);
break;
case MESSAGE_POST_PROGRESS:
result.mTask.onProgressUpdate(result.mData);
break;
}
}
}
生成AsyncTaskResult
private static class AsyncTaskResult<Data> {
final AsyncTask mTask;
final Data[] mData;
AsyncTaskResult(AsyncTask task, Data... data) {
mTask = task;
mData = data;
}
}
這里在Handler中進程處理的是：
result.mTask.finish(result.mData[0]);
private void finish(Result result) {
if (isCancelled()) {
onCancelled(result);
} else {
onPostExecute(result);//運行在UI線程
}
mStatus = Status.FINISHED;
}
==到這里明白了在WorkerRunnable中回調方法執行doInBackground()并且將返回結果交給主線程Handler處理==
[2]
mFuture = new FutureTask<Result>(mWorker) {
@Override
protected void done() {
try {
postResultIfNotInvoked(get());
} catch (Exception e) {
postResultIfNotInvoked(null);
}
}
};
對于FutureTask來說,將mWorker設置進去命名callable
public FutureTask(Callable<V> callable) {
if (callable == null)
throw new NullPointerException();
this.callable = callable;
this.state = NEW; // ensure visibility of callable
}
此時構造完成，下面看看當我們使用的時候
String[] urls = {
"http://blog.csdn.net/iispring/article/details/47115879",
"http://blog.csdn.net/iispring/article/details/47180325",
"http://blog.csdn.net/iispring/article/details/47300819",
"http://blog.csdn.net/iispring/article/details/47320407",
"http://blog.csdn.net/iispring/article/details/47622705"
};
DownloadTask downloadTask = new DownloadTask();//自定義
downloadTask.execute(urls);
我們會執行execute方法
public static final Executor SERIAL_EXECUTOR = Utils.hasHoneycomb() ? new SerialExecutor() :
Executors.newSingleThreadExecutor(sThreadFactory);
private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
public final AsyncTask<Params, Progress, Result> execute(Params... params) {
return executeOnExecutor(sDefaultExecutor, params);
}
如果SDK版本大于11，生成SerialExecutor對象，否則用一個線程池
對于SerialExecutor是
@TargetApi(11)
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);
}
}
}
這里暫時不看對應這里的分析
我們繼續看主邏輯
public final AsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec,
Params... params) {
if (mStatus != Status.PENDING) {
switch (mStatus) {
case RUNNING:
throw new IllegalStateException("Cannot execute task:"
+ " the task is already running.");
case FINISHED:
throw new IllegalStateException("Cannot execute task:"
+ " the task has already been executed "
+ "(a task can be executed only once)");
}
}
mStatus = Status.RUNNING;
onPreExecute();//剛進來走這里
mWorker.mParams = params;//將參數給mWorker
exec.execute(mFuture);//執行mFutrue
return this;
}
==執行onPreExecute方法，這個實現是空，所以是對于子類進行復寫的。也就是任務執行前的邏輯==
==著重看exec.execute(mFuture);==
所以執行的是SerialExecutor類的execute方法
public synchronized void execute(final Runnable r) {
mTasks.offer(new Runnable() {
public void run() {
try {
r.run();
} finally {
scheduleNext();
}
}
});
if (mActive == null) {
scheduleNext();
}
}
SerialExecutor將對應的mFuture添加到mTasks中，完了執行scheduleNext()
public static final Executor THREAD_POOL_EXECUTOR
= new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory,
new ThreadPoolExecutor.DiscardOldestPolicy());
protected synchronized void scheduleNext() {
if ((mActive = mTasks.poll()) != null) {
THREAD_POOL_EXECUTOR.execute(mActive);
}
}
用一個線程池去執行剛才的任務，對于任務先執行run方法
也就是說執行的是FutureTask的run方法，然后執行下一個任務的run方法。
==也就是一個線程池執行FutureTask的run方法==
public void run() {
if (state != NEW ||
!U.compareAndSwapObject(this, RUNNER, 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 = null;
int s = state;
if (s >= INTERRUPTING)
handlePossibleCancellationInterrupt(s);
}
}
run方法在調用c.call()，c是callable，是構造時候傳遞進來的mWorker,所以調用的是mWorker的call
mWorker = new WorkerRunnable<Params, Result>() {
public Result call() throws Exception {
mTaskInvoked.set(true);
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
return postResult(doInBackground(mParams));
}
};
執行的是回調里面的東西。與此同時在run方法中有set(result);
也就是說將WorkerRunnable.call()的返回結果返進行set。
protected void set(V v) {
if (U.compareAndSwapInt(this, STATE, NEW, COMPLETING)) {
outcome = v;//核心
U.putOrderedInt(this, STATE, NORMAL); // final state
finishCompletion();//[1]這個方法調用down
}
}
==現在知道了outcome是我們在mWorker中call的返回結果==
[1]
private void finishCompletion() {
for (WaitNode q; (q = waiters) != null;) {
if (U.compareAndSwapObject(this, WAITERS, q, null)) {
for (;;) {
Thread t = q.thread;
if (t != null) {
q.thread = null;
LockSupport.unpark(t);
}
WaitNode next = q.next;
if (next == null)
break;
q.next = null; // unlink to help gc
q = next;
}
break;
}
}
done();//調用
callable = null; // to reduce footprint
}
也就是執行
mFuture = new FutureTask<Result>(mWorker) {
@Override
protected void done() {
try {
postResultIfNotInvoked(get());
} catch (Exception e) {
postResultIfNotInvoked(null);
}
}
};
其中get
public V get() throws InterruptedException, ExecutionException {
int s = state;
if (s <= COMPLETING)
s = awaitDone(false, 0L);
return report(s);
}
private V report(int s) throws ExecutionException {
Object x = outcome;//這個就是worker產生的結果
if (s == NORMAL)
return (V)x;
if (s >= CANCELLED)
throw new CancellationException();
throw new ExecutionException((Throwable)x);
}
==所以在子線程中執行了FutureTask.run()，得到了傳遞構造中的worker調用了call()得到的返回值set到了outcome中，隨后調用了FutureTask.done()，get得到的返回值傳入postResultIfNotInvoked(get())==
private void postResultIfNotInvoked(Result result) {
final boolean wasTaskInvoked = mTaskInvoked.get();
if (!wasTaskInvoked) {
postResult(result);
}
}
private Result postResult(Result result) {
@SuppressWarnings("unchecked")
Message message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
new AsyncTaskResult<Result>(this, result));
message.sendToTarget();
return result;
}
將結果放入了主線程中執行。
