I'm making a thread the usual way and named it "Encoder". If the app closes and restarts again the object of the Thread is destroyed and recreated. Is there a way to get to know if the Thread that I started before is still running or not. ?
You're designing your app wrong.
If the Thread will carry on the work after the activity died, and a new activity should be able to "pick up where the last one left", you should be using a Service to do this work and bind your activity to it.
You can read more about it and how to implement it here: http://developer.android.com/guide/components/bound-services.html
You can use method .isAlive();
From doc:
Tests if this thread is alive. A thread is alive if it has been
started and has not yet died.
Related
I would like to better understand what happens to a Thread or a AsyncTask when activity is destroyed.
So in this scenario, a Thread or AsyncTask would be started from activity, and user hits home button and onDestroy gets called triggering GC before either Thread of AsyncTask had a chance to finish.
Which one is more likely to run till completion in this scenario Thread/Runnable or an AsyncTask ?
Thanks.
Both will run
But the problem is if you have a reference to the killed activity on Thread of AsyncTask it will leak, and that is a problem you need to solve to make long running tasks synchronized with UI
If you've got a bigger task, I'd suggest you to spin up a Service, which are more easy to handle in Android context
AsyncTask based on thread so there is no huge difference in it's behaviour both will run after onDestroy. To avoid this behaviour you could use Loaders or manually stop execution of AsyncTasks/Threads in onDestroy method.
What is recommended to do for networking job that should fetch and update new data? I see different answers on that issue.
To create a Service that will run inside a new Thread that should make all the network job OR to create a new Thread that will start a Service inside that Thread?
You can't make a Service that runs inside a Thread, so that possibility is impossible. You need a Thread (or AsyncTask) to do any network request. If you want the app to continue to do network requests even if the current Activity is finished, then yes you need to create that Thread (or AsyncTask) in a Service.
In android all The network operations are to be done within a thread. Even if you are creating a service all network operations will be done within a thread.
Service within a thread is not possible.
Now if You want your network operations to be available in multiple activities you should create a service otherwise A separate network thread within an activity will do the job.
IntentService initializes on the main thread in onCreate and runs in a separate thread otherwise. No need to deal with extra threads in this case. A Service runs in the main thread and requires that you handle the threading (if needed). It would be best to prototype an IntentService since you're just making a network call. If the network call is short, then just use an AsyncTask.
I think you need IntentService. No need to confuse on Service inside Thread. Start Service inside background thread or start a service with background thread .Both are same.
It is always better to call thread inside service rather than service inside thread because service is a component of android so it is having some priority level. On the other hand Thread is not a part of Android component so it is having no priority compared to service.
So in case of low memory when Android system starts killing application, it will first kill thread that contains the service because of its lower or no priority. And if you have used Service containing thread then you are good. Hope it helps :)
Service callbacks run on the main thread just like activities' (unless otherwise specified). I seem to stumble upon lots of advice here on SO that goes something like "start a thread in a service [to do work in the background]". That doesn't make sense to me. What does it matter if I start a thread from activity code compared to service code, just as long as there exists a started service component in the application process?
If the answer is what I think (that it doesn't matter) then it's a shame that people give the impression that a service object needs to be somehow related to the background thread.
The term "background" can be misleading when it comes to Services as it can have two meanings. Services are used, simplistically talking, to run tasks even if there is no Activity of your application running. To clarify, think of a music player; you want the music to still play even if the Activity is not running. That is the definition of background that doesn't have to do with Threads; you are running a portion of your application in the background because you do not have any visible component of your app on the screen (maybe some Notification but no full screen UI).
Now, lets say you want to download some data from the internet. As you might know, you cannot perform long running tasks in the UI Thread (as of API 11+ you will get a NetworkOnMainThreadException), so you need to use a background Thread. Let's say you do not want to use an AsyncTask to download the content because a Service is better suited for your needs. In this case, you will have to start the Service on a background Thread. That is the second meaning of background, which basically means creating a new Thread. Android provides a class that does exactly this; IntentService. It is a Service that runs on a background Thread and that it finishes itself when the given task is done.
It does not matter where you actually start a thread if the lifetime of that thread is reflected via your app process state: http://developer.android.com/guide/components/processes-and-threads.html#Lifecycle
Android does not care if there is a Thread running or not. Threads just run even when your app is considered an empty process "that doesn't hold any active application components." Don't abuse that, since users don't want that apps are secretly active although they look dead.
If you want (and you should) that Android does not kill you randomly although your threads are not done you have to make sure that you keep e.g. a Service in started state.
Creating a thread from within a Service (or just using IntentService) will primarily result in better, simpler & cleaner code. For example because a Service has a Context and you can't leak your Activity from there. You also get free callbacks from the system.
And leaks via threads are extremely easy.
new Thread(new Runnable() {
#Override
public void run() {
SystemClock.sleep(Long.MAX_VALUE);
}
}).start();
Will leak your activity if you just put it in e.g. onCreate because the anonymous inner Runnable keeps a reference to your Activity and will not release it until the thread stops running and is itself garbage collected.
In case you really know what you are doing, feel free to start threads in Activities and sync their lifecycle manually to some empty Service. I would not recommend it because it's unlikely to be less work to do that correctly.
Pardon my questions, as I'm still very new to programming so I don't fully understand the concepts of mainthreads, and async tasks, and services, and threads. I'm reading the documentation about Services for Android because I want to perform some tasks off the main thread. It says:
If you need to perform work outside your main thread, but only while
the user is interacting with your application, then you should
probably instead create a new thread and not a service.
1.Are they saying that a "thread" stops immediately after you leave the app (i.e: Home button)?
For example, if you want to play some music, but only while your
activity is running, you might create a thread in onCreate(), start
running it in onStart(), then stop it in onStop(). Also consider using
AsyncTask or HandlerThread, instead of the traditional Thread class.
See the Processes and Threading document for more information about
threads.
2.If threads are baked into Java, why does android have AsyncTasks?
Remember that if you do use a service, it still runs in your
application's main thread by default, so you should still create a new
thread within the service if it performs intensive or blocking
operations.
3.Does this basically mean, that almost every service is basically going to have a thread created inside it?
4.Would it be bad to start an AsyncTask inside of a service?
1.Are they saying that a "thread" stops immediately after you leave the app (i.e: Home button)?
A Thread should be destroyed when the Thread that started it is destroyed. So, if you start a Thread in an Activity then it should be destroyed when that Activity is destroyed or transferred to a Service. For instance, you can start music in a Thread and update the songs there but if you want it to keep playing when the Activity is destroyed then it should be moved to a Service
2.If threads are baked into Java, why does android have AsyncTasks?
An AsyncTask allows you to perform background work and easily update the UI before, during, and after the background work is done by utilizing any of its built-in methods except for doInBackground() because it is the only one that doesn't run on the UI Thread
3.Does this basically mean, that almost every service is basically going to have a thread created inside it?
Not necessarily but you could create a Thread inside of it
4.Would it be bad to start an AsyncTask inside of a service?
No. You could do this.
AsyncTask is a great way to do background work. Its methods make it very easy to update the UI. But you need to read through the documentation carefully (maybe even a few times) to make sure you completely understand how to use them. Also, remember that these are for short-lived operations so they can be good for downloading network data but shouldn't be used for things that last more than a few seconds (According to the docs)
A thread doesn't stop immediately when you leave the app. The suggestion to use a separate thread is only so you don't block your app's GUI.
AsyncTasks actually use a ThreadPool behind the scenes as creating a thread is an expensive process. If you have many short lived tasks, using AsyncTask is just a quick, easy, but efficient way to execute them without blocking your application's GUI.
Yes, essentially. A service is more heavy weight than a thread though. Using a service in place of a thread is not a good idea. Also services can actually be made to execute on a whole other process. Just FYI.
No. It would be a good idea, if you've many short lived tasks to execute.
If you are only trying to execute tasks off the main thread, you don't need a service. Just create another thread.
AsyncTask behind the scenes just submits your task to a thread pool for execution. If you have many short lived tasks, like parsing networking traffic, AsyncTask is great.
However, if you are handling a huge amount of requests, you might want more control over the thread pool executing your tasks.
No
Because a main thread controls the UI while asynctasks can make heavier tasks while keeping the UI lag-free.
No, but if you want your service to make heavy lifting like loading stuff from internet then it should use an asynctask. Most services are used to load data from internet so most of them have asynctasks. Note that for the service to be kept alive after the activity dies, you must specify it. Services by default die along with the activity unless configured properly
No
You might be confusing by thread and task and process.Task is small kind of process.An process
is a pro-gramme that running in your system example when start your task-manager it is showing all the process running like Internet-explorer but thread is small lightweight process means you can say sub-process that in execution for performing some task but asynchronous in android is just similar to thread but it may-be long.Take a example in android you are playing temple-run in android-phone ,and some-one is calling you so that high priority task will performed and current thread is paused there and so many method are there
like onCreate() ,onPause(),you can understand it.
I write a program which needs to receive informations from a server. I use asynchronous threads to accomplish that. But when the user clicks on another item a new thread gets launched. If the first one has not yet finished for example because of a network issue, the second thread ends and sets the UI information. Then the first one ends and overwrites it again. So how can I stop the first thread when the user clicks on another item?
I got that:
Thread asyncThread = new Thread(task);
asyncThread.start();
But from what I can see in the Thread object, there is no way to stop the thread (only deprecated .stop()), but I don't want to use deprecated stuff for new programs.
In JavaFX it's recommended to use Service, a service provides method like, stop(), cancel(), restart()... Look my answer to this JavaFX GUI stuck to show how use Service.