Thanks so much for the response! If you'll indulge me with a few more
questions...
So I instantiate the handler in the onCreate() method of my Application,
which I assume means it's tied to the UI thread.
The method that removes and re-sends messages is called primarily on the UI
thread, but can also be called from an IntentService that I use to handle
network communication. Since the service is executed by a thread other
than the UI thread it appears that I do need to synchronize.
To give some more detail on my goals for this: I'm attempting to use the
handler to track both user inactivity and server session expiration. The
Service calls a "session refreshed" method to remove session-related
delayed messages and re-add them with a new delay. The UI thread calls an
"user activity occurred" method to indicate the user "did something"; that
method removes inactivity-related delayed messages and re-adds them with a
new delay.
One other kink: I also have code to respond to SCREEN_ON and SCREEN_OFF.
At screen off I remove all messages from the handler; at screen on I
re-send each message that was queued at the point at which screen off
occurred, albeit with a revised delay to account for the time that elapsed
while the screen was off.
On Tue, Oct 30, 2012 at 9:43 AM, Streets Of Boston
<flyingdutc...@gmail.com>wrote:
> It depends which thread is callling the code-snippet you show above (the
> one calling 'removeMessage').
>
> If your code, calling 'removeMessage', is run on the same thread that is
> tied to the *handler*, you're fine. The message you sent will not be
> handled/run until your code finishes first. No extra work necessary.
>
> If your code, calling 'removeMessage' is run on another thread than the
> one tied to the *handler*, you need to sync it up. This could be as
> simple as send another message on that handler that will call
> 'removeMessage': E.g.:
> handler.post(new Runnable() {
> public void run() {
> // Right now, calling 'removeMessages', etc. is done
> // on the handler's thread as well.
> handler.removeMessages(MSG_**ONE);
> handler.removeMessages(MSG_**TWO);
> ...
>
> if (conditionOne)
> handler.**sendEmptyMessageDelayed(MSG_**ONE, timeoutOne);
>
> if (conditionTwo)
> handler.**sendEmptyMessageDelayed(MSG_**TWO, timeoutTwo);
> }
> });
>
> Since both the 'removeMessages' and 'sendEmptyMessageDelayed' are called
> on 'handler' the Runnable needs to finish first before any other message
> sent to 'handler' can be executed.
>
>
> On Tuesday, October 30, 2012 9:17:39 AM UTC-4, Jay Howard wrote:
>>
>> I'm using a timer to manage timeout events, and would like to ensure that
>> a particular method runs atomically without the handler issuing messages
>> while the method is executing. Its basic form is:
>>
>> handler.removeMessages(MSG_**ONE);
>> handler.removeMessages(MSG_**TWO);
>> ...
>>
>> if (conditionOne)
>> handler.**sendEmptyMessageDelayed(MSG_**ONE, timeoutOne);
>>
>> if (conditionTwo)
>> handler.**sendEmptyMessageDelayed(MSG_**TWO, timeoutTwo);
>>
>> ...
>>
>> What I want to avoid is a situation where, before the removeMessages()
>> calls execute, one of the messages reaches its timeout and is delivered to
>> the message queue, then I send a duplicate one immediately after. My goal
>> is to guarantee that there is never more than one of each message type "in
>> flight" on the handler at any given time.
>>
>> Does the Handler class synchronize on MessageQueue when delivering its
>> messages? If so, then could I just synchronize on the MessageQueue? Or
>> would that be a terrible idea, since it's used by entities other than just
>> my Handler?
>>
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