memory leak about AsyncTask

[cuixiaoyiyi]

According to our research, there are misuses about the following AsyncTask class:
( in com.tananaev.logcat. MainActivity)

private ReaderTask readerTask;
//……
private class ReaderTask extends AsyncTask<Void, StatusUpdate, Void> 

The problems is:

1. It is inner class. It holds strong reference to the GUI element of Activity( MainActivity ), which can lead to memory leak when the Activity is destroyed and the AsyncTask did not finish.

I think we can make following changes to fix the misuse problems:

1. I think the GUI-related fields should be wrapped into WeakReference. Take
   private final MainActivity _context as example, it can be changed to private final WeakReference<MainActivity> _context.

[tananaev]

Why would it leak? We stop task on destruction.

[cuixiaoyiyi]

You stop task on destruction by invoking the cancel(…) method.

AsyncTask.java
   * @param mayInterruptIfRunning <tt>true</tt> if the thread executing this
     *        task should be interrupted; otherwise, in-progress tasks are allowed
     *        to complete.
     *
     * @return <tt>false</tt> if the task could not be cancelled,
     *         typically because it has already completed normally;
     *         <tt>true</tt> otherwise
     *
     * @see #isCancelled()
     * @see #onCancelled(Object)
     */
    public final boolean cancel(boolean mayInterruptIfRunning) {
        mCancelled.set(true);
        return mFuture.cancel(mayInterruptIfRunning);
    }

FutureTask.java
    public boolean cancel(boolean mayInterruptIfRunning) {
        if (!(state == NEW &&
              U.compareAndSwapInt(this, STATE, NEW,
                  mayInterruptIfRunning ? INTERRUPTING : CANCELLED)))
            return false;
        try {    // in case call to interrupt throws exception
            if (mayInterruptIfRunning) {
                try {
                    Thread t = runner;
                    if (t != null)
                        t.interrupt();
                } finally { // final state
                    U.putOrderedInt(this, STATE, INTERRUPTED);
                }
            }
        } finally {
            finishCompletion();
        }
        return true;
    }

Invoking cancel(true) will interrupt the thread but there is no guarantee that the thread will be terminated. So WeakReference is recommended.

[tananaev]

OK, feel free to send a pull request with the fix.