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I was reading a article in Android developer blog Process and Threads which talks about creating new process for specific component of Application. But I failed to understand when will creating a new process in my application becomes a absolute need. Could you please help me understand following doubts I have in this regard.

  1. When as a developer I should feel I need to have a separate process for a Android component/s?
  2. Does introducing a new process has any side effect on application's overall performance?

Any other info is greatly appreciated.

Thanks, SKU

sku
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  • Looks like this StackOverflow thread is better documented : [Follow this link :)](https://stackoverflow.com/questions/4658511/android-how-to-decide-whether-to-run-a-service-in-a-separate-process) – Tobliug Jun 21 '17 at 07:32

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Having a separate process can be useful if there are components of your application that do not necessarily need to both be running to be useful to the user, and the background task is critical to application "correctness" (either now or in the future). The classic example of this is an app that has a service where the service saves or uploads some data that is critical to your application (critical meaning the only way to get the data back is to have the user re-enter it!). The service might be responsible for doing something like uploading or saving data, while the activity is just the interface for the user. So developers should decouple these two components to prevent problems that may arise from my next point..

Android was designed to run in a resource (especially memory) constrained environment, so processes deemed unimportant are killed periodically to open up memory for important ones by the "low memory killer" (LMK) (if you Google this you'll get tons of information on the topic). Things like foreground processes are understandably given a higher priority since they're currently in use, but they're sometimes killed off as well for reasons like consuming too much memory. Now, imagine you need to save off some data to a database after the user does something in the app and you use a service to do so to ensure that it is done even if the user navigates away from the app. Unless you create the service in its own process the process containing both the activity and the service is likely to be killed since the process belongs to a non-foreground activity. However it is not always necessary to place the service in its own process, oftentimes simply giving the service its own thread will suffice; it's very application specific. I would only place a service in its own process if it took longer than maybe a few seconds (long enough for the user to navigate away from my application and for the LMK to step in) to perform some task in the background and that task related to the "correctness" of my application (I.E. saving data for later). For something like caching, stick to threads, since if the process gets prematurely killed you can just recreate that data later.

Another reason to have a separate process is if you're running a global service (a service that can be used by applications other than your own) that maybe you provide an interface with via an Activity for configuration.

As for the performance question, there will definitely be a performance hit for something like this. Interprocess communication is not cheap, so you should really only use a separate process if you fit into a specific use case, like the ones mentioned above. Also, there's a certain amount of memory overhead for maintaining a process, so that's another performance hit.

Ethan
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1.)You need to do something on seperate process or thread when you don't want your app to behave slowly. As by introducing threads you force your app not to run on UI thread. Thus making your app responsive to other events. For Example : you can use threads when you have to fetch some data from web service so that it happens in background and doesn't effect your app.

2.)Threads should not be used..We should use AsyncTask or loaders rather in android.

Rookie
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    I understand and have enjoyed the benefits of using a separate thread (in form of Handler, AsyncTask and worker Thread) in my applications. But it does no where mean that creating a new thread in any of above mentioned fashion will create a new process. Do you feel using a separate process is to group such threads which have common resource usage? – sku May 13 '12 at 20:43
  • No, allowing components in different applications to share a same process helps reducing resource usage. Creating new process will increase the resource utilization but sometimes it might be neccessary. For example you might want your serice to be running even if the app running in different process crashes. – Rookie May 13 '12 at 21:09
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    I wouldn't say threads should NOT be used. AsyncTask makes specific TYPES of task a lot easier to achieve programatically e.g. some task that has a finite period of execution that should not be done on the main thread such as downloading a file. – D-Dᴙum May 13 '12 at 21:23
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    @Raghav, I understand your point on resource utilization. I feel there should be many other uses of having separate process. Thanks, for getting the thread started. – sku May 13 '12 at 22:12
  • AsyncTasks are not heavy duty enough for a lot of threading tasks in Android, Handlers and HandlerThreads are preferred in Android for such heavy duty tasks where a more general interface is needed than the one provided by AsyncTask. Also, @Rookie, you're incorrectly conflating the general topic of a thread with the Thread class provided in Java... – Ethan Feb 10 '16 at 18:24
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1.) In android 4.0 (and possibly 3.0, not sure though) The device does not let you use the HTTP Agent in the main thread, for this slows the UI.. This is when threads come in handy.

Also with the use of functions that need alot of cpu, if these are run in the UI thread, the UI will lag and not respond until the function finishes.

2.) as stated at 1, it will actually improve the visual performance of your app ;)

Wampie Driessen
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    Hi Wampie, I do understand why I need to have a separate thread for time consuming operations. But I fail to understand why one need a separate process for any component of Android. New threads in your application will be created in the existing application process until otherwise specified. I am still searching for an answer on "why one require to have separate process altogether" – sku May 13 '12 at 20:47