Hello,
I have put together the following code that illustrates that
apparently the answer to my question
is that a thread can call join() on another thread which has not yet
started (as s.join() below will
be run before s.run()) resulting in the output "Hello World Bye".
Regards,
JG
final Thread s = new Thread() {
@Override
public void run() {
System.out.println("World");
}
};
Thread t = new Thread() {
@Override
public void run() {
System.out.println("Hello");
try { sleep(5000); } catch (Exception e) { e.printStackTrace(); }
s.run();
}
};
t.run();
try { s.join(); } catch (InterruptedException e) { e.printStackTrace(); }
System.out.println("Bye");
2012/2/9 John Goche <[email protected]>:
> Hi all,
>
> The problem I am having is that the thread I need to call join() on so as
> to wait for completion may not even yet be started when I call join(). Is it
> legal in Java to call join() on a thread which is not running, but which will
> eventually be run by a third thread?
>
> Thanks,
>
> JG
>
> 2012/2/9 John Goche <[email protected]>:
>> Basically sendRequest() invokes a thread which calls runOnUiThread with
>> a new Runnable() which in turn also invokes a new Thread(). It is this latter
>> thread which I need to wait for to finish. I thought of using the join()
>> method
>> to force thread completion prior to continuation at a specific spot but I am
>> somewhat new to thread programming and I am not entirely sure
>> about how to set things up. Will give it another go...
>>
>> Thanks for your help,
>>
>> JG
>>
>> 2012/2/9 John Goche <[email protected]>:
>>> Thanks Kostya!
>>>
>>> I have traced the code with the debugger and found that even though
>>> notify() is being called from within a thread instantiated from
>>> sendRequest()
>>> (which is not the same thread as sendRequest()'s thread), the notify() is
>>> being called before the wait().
>>>
>>> I am assuming that if I call notify() before wait() the notification gets
>>> lost?
>>> If this is not so, someone please let me know.
>>>
>>> The problem I am having is that sendRequest() launches a new thead s,
>>> and I need to be sure thread s completes before the code proceeds past
>>> what I have marked with wait().
>>>
>>> Any ideas on how to solve this synchronization problem?
>>>
>>> Thanks,
>>>
>>> John Goche
>>>
>>>
>>> 2012/2/9 Kostya Vasilyev <[email protected]>:
>>>> Are you calling notify() from inside sendRequest()?
>>>>
>>>>
>>>> If so, it's the same thread, and notify has nothing to do.
>>>>
>>>> http://developer.android.com/reference/java/lang/Object.html#notify()
>>>>
>>>> Causes a thread which is waiting on this object's monitor (by means of
>>>> calling one of the wait() methods) to be woken up
>>>>
>>>>
>>>> From looking at the code you posted, there is no thread waiting on the lock
>>>> because you only have one worker thread, and when it's calling notify it's,
>>>> well, calling notify and not waiting on a wait().
>>>>
>>>>
>>>> For debugging, set a breakpoint at lock.notify, and use the DDMS thread
>>>> monitor or the debugger window to examine your threads.
>>>>
>>>>
>>>> You might want to look at this package, which provides higher-level
>>>> concurrency classes, and try to find one that fits what you're trying to
>>>> do:
>>>>
>>>> http://developer.android.com/reference/java/util/concurrent/package-summary.html
>>>>
>>>> ( ThreadPoolExecutor? BlockingQueue? )
>>>>
>>>> -- Kostya
>>>>
>>>> 10 февраля 2012 г. 0:41 пользователь John Goche
>>>> <[email protected]>
>>>> написал:
>>>>>
>>>>> Dear Android developers,
>>>>>
>>>>> I am having the following issue in Android:
>>>>>
>>>>> In one class I am having:
>>>>>
>>>>> --------------------------------------------
>>>>>
>>>>> final Object lock = new Object();
>>>>>
>>>>> Thread thread;
>>>>>
>>>>> @Override
>>>>> public void onCreate(Bundle savedInstanceState) {
>>>>>
>>>>> super.onCreate(savedInstanceState);
>>>>>
>>>>> thread = new Thread() {
>>>>>
>>>>> @Override
>>>>> public void run() {
>>>>>
>>>>> sendRequest("foo");
>>>>>
>>>>> synchronized(lock) {
>>>>>
>>>>> try { lock.wait(); } catch (InterruptedException e) {
>>>>> e.printStackTrace(); }
>>>>>
>>>>> }
>>>>>
>>>>> System.out.println("GOT HERE!!!");
>>>>>
>>>>> ------------------------
>>>>>
>>>>> which causes the sendRequest() to do a bunch of stuff. When such stuff
>>>>> finishes I call:
>>>>>
>>>>> System.out.println("Notifying thread...");
>>>>> synchronized(lock) {
>>>>> lock.notify();
>>>>> }
>>>>> System.out.println("Thread notified.");
>>>>>
>>>>> -------------------------
>>>>>
>>>>> and this code executed until the "Thread notified." println()
>>>>> statement. But then I do
>>>>> not see the waiting thread resume from where I called wait(). Here is the
>>>>> output
>>>>> from adb logcat:
>>>>>
>>>>> I/System.out( 2395): Thread notified.
>>>>> W/ActivityManager( 60): Launch timeout has expired, giving up wake lock!
>>>>>
>>>>> I do not see where I am going wrong. Any ideas why the code is not
>>>>> working as expected?
>>>>>
>>>>> Thanks,
>>>>>
>>>>> John Goche
>>>>>
>>>>> --
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>>>>
>>>>
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