Basically, there is a Google way, which suggests using Service for long running operations (which I use at the time). On the other hand, there are a lot of examples in community by honored developers, which avoid using Service and at most incorporate Fragment's setRetainInstance(boolean retain).
While Google has declared that a lot of bad stuff might happen if we don't use a Service, I still feel anxious because there are, it seems, so many projects leaving Service aside.
Can you consolidate the Google's case or provide suggestions for abandoning Service?
P.S. I'm developing "classic" rest-client applications.
P.S.S. I forgot to mention that Service is used in pair with ContentProvider(for cachging purposes, guard against system app forceshutdowns).
Thanks.
If the network request is very likely to take under a second, or if you don't mind it if your process terminates before the request completes, using simple threading from the UI layer is fine, IMHO.
But once the user leaves your app (HOME, responds to an incoming call, etc.), the lifetime of your process is limited, and it could be very short if you do not have a service to tell the OS that you're still doing important work for the user.
So, if the network request is more in the 1-15 second range, and you'd like to feel fairly confident that the work will run to completion, use an IntentService or something along those lines.
If the network request is likely to be longer than that, such as a large download, now you have to worry about the device going to sleep and such. My WakefulIntentService was designed for this sort of scenario, where it will keep the device awake long enough to get the work done, then let the device go back asleep.
Some developers use services for all significant network I/O, skipping them only for truly ephemeral stuff like thumbnail images to populate a ListView or RecyclerView. So long as the service is only running when it is actively delivering value to the user, this is perfectly fine.
Related
I have been developing for Android for little less then 2 years, and I am still puzzled by this seemingly simple question.
When should one implement a service?
From my experience there are some rare cases but I am questioning this because on every phone there are quite a lot of them running and I doubt it's just a poor application design.
This is essentially core of my question but following are some of my experiences and thoughts about the subject which can explain my question in more detail.
In all apps that I have developed only one really required a service. It was a background sound recorder and I was using it as Foreground service with notification since I wanted buttons to be able to control it (like music players do for example).
Except this I never really saw a requirement for the constantly running service because:
A) Intent listeners (Manifest registered BroadcastReceivers) are quite a useful feature and using them as you know is usually enough for many use-cases (for example showing notifications).
B) If scheduled execution is a must one can subscribe to alarm events.
C) I know that service in Android is quite different then for example in Windows since in Android services are just a "package" to organize your code in and have a the system manage the lifetime of the object. Services use the Main Thread but it's customary to spawn new threads in them.
D) In the development documentation services are suggested for network communication and background calculations but I don't get why you should not just use AsyncTasks for that. I am a big fan of these and use them extensively for lot of things from downloading data from the internet to doing FFT calculations under time critical conditions.
E) I get the usefulness of Foreground services but why are people using background services so much (excluding the system apps).
Those are my thoughts about the SERVICE and I hope someone with more experience will be able to explain these PROS and CONS (along with others that I probably missed).
When should one implement a service?
When you have work -- delivering value to the user -- that:
Needs some time to complete, perhaps longer than you have time for in the component wishing the work to be done, or
Is delivering that value under user control (e.g., music player, controlled by play/pause buttons in a UI), or
In rare cases, needs to be running continuously, as it delivers value continuously
there are quite a lot of them running and I doubt it's just a poor application design
Some are likely to be poor implementations, either due to technical misunderstandings, or other concerns (e.g., making marketing happy) trumping making users happy.
It was a background sound recorder and I was using it as Foreground service with notification since I wanted buttons to be able to control it (like music players do for example)
That is a reasonable use for a service, IMHO.
Intent listeners are quite a useful feature and using them as you know is usually enough for many use-cases (for example showing notifications)
I assume that by "Intent listeners" you mean manifest-registered BroadcastReceivers. In that case, if the work to be done by the BroadcastReceiver will take more than a millisecond, that work should be delegated to an IntentService for completion. onReceive() is called on the main application thread, and it is not safe for a manifest-registered BroadcastReceiver to fork a bare thread, as the process could go away shortly after onReceive() returns. However, in these cases, the service is usually short-lived (e.g., do some network I/O and disk I/O, then go away).
In the development documentation services are suggested for network communication and background calculations but I don't get why you should not just use AsyncTasks for that
An AsyncTask is a fine solution for background work that is:
Requested by the UI (activity or fragment), and
Will take less than a second or so, and
Is non-critical
For example, if you are downloading avatars to show in a ListView, AsyncTask is probably a fine choice, whether you use them directly or use some image-fetching library that uses them internally.
Conversely, if the user buys an MP3 through your app, and you need to download that MP3 file, an AsyncTask is not a good solution. That could easily take over a second. While the download is going on, the user could switch away from the app (e.g., press HOME). At that point, your process is eligible to be terminated... perhaps before your download is complete. Using an IntentService to manage the download is a signal to the OS that you are really doing work here, adding value to the user, and so the process will be left alone for a little while.
Note that if the background work might take 15+ seconds, WakefulBroadcastReceiver or my WakefulIntentService is probably a good idea, so the device does not fall asleep while you are trying to wrap up this bit of work.
I can name some of the Service uses from my experience:
to implement
location listener,
sound module, generating various voices
in app content updates,
API, provide services to other apps
in app billing
Communication with webservices (if requests frequency is high)
actually (excluding 5.) they all are working for the whole app duration, they are using some of the other android services, also they manage their state. I suppose one of the important thing here is state management during application life cycle changes.
I prefer to look at AsyncTasks in a same way as Executors (ExecutorService), they should be executed sequentially and for small tasks.
In the android website, you can find a table when to use Service, Thread, or WorkManager (the new API for scheduling jobs, currently in alpha as of this comment posted). https://developer.android.com/guide/background/#table-choose
The website also state that you need to use started service only as last resort. The Android platform may not support started services in the future. Refer to this link https://developer.android.com/topic/performance/scheduling#services
You should avoid using started services that run perpetually or perform periodic work, since they continue to use device resources even when they aren't performing useful tasks. Instead, you should use other solutions that this page describes, and that provide native lifecycle management. Use started services only as a last resort. The Android platform may not support started services in the future.
If you consider UI and bound services, u would think that both can exist and not be doing anything for certian periods. In such scenarios, your UI can be recreated a lot of times however service does not. And this is where service is important. Lets say you are processing images and then rotate device you want processing to continue while UI is being recreated. You recording a voice and then rotate device. These are one of the places where I find service very important. (Having lot of heavy data processing, interaction with web, that could be few seconds)
As relatively new to the android platform I was given the task of implementing a email client. For this I want to use an service that allways run in the background (client should allways receive emails as soon as the server gets them, requirement from the customer).
Now I've looked into the Service's in android, but can't seem to find any good answer on whether or not the Service should be local or remote.
What would the main advantages/disadvantages be with choosing one over the other? Bare in mind the Service must be running at all times. I know, I know. BAD. But it is essential to core features of the application.
First, the correct/efficient way to do instant notifications from a remote server like this on Android is to use Google Cloud Messaging. GCM lets you remotely wake up the device by sending an Intent to your application, which you can then use as a signal to fetch the message from the server, post a notification to the status bar, etc.
Doing what you're describing with an eternally running service will have a significant effect on battery life unless you get everything exactly right. Keeping the phone awake all the time is not a viable option. Use GCM and do not roll your own solution for this.
But since your question was more general about whether to run a service in a separate process, in general simpler is better and in this case simpler means running in the same process. You'll have access to all of the various elements of your app's process in memory and in general you will probably have a much easier time. Your events will all happen on the same main thread's Looper. Everything will be much more straightforward.
If you don't already have a very good reason for using a separate process for your service, you should run it in the same process.
Generally I don't know the reason why you can want to use another process. If you will - you'll have to deal with Inter-process communications, with all this AIDL, Parcels etc.
And if you will keep the same process - it will be much easier to transfer the data between your components.
The only reasons to make several processes I think is to try to avoid Android Heap budget limitation. You can try to move heavy objects between processes and try to double your limit. However I think you don't need this, also it's bad way too.
So I will recommend not to play with processes and keep things as simple as possible.
Good luck
I'm building a program which interfaces with a device which runs its own internal web server. I communicate with the device via a web API.
Basically what happens is that a GUI is presented to the user, where the user can make certain modifications to the device. These changes are communicated to the device, and results are returned through XML. The device needs to converse with the program in the background more or less continually (say every 15s or so) to update certain values to the user.
My structure that I'm envisioning is something like this:
UI - Main - Networking - XML Parser.
I'm looking for advice on how to manage these. I understand the UI thread should be separate to provide a smooth experience to users. I also understand that the networking should be at least an asynchronous task. I'm not so sure about how to handle their interaction, and make sure things are happening smoothly and effectively.
My idea is that Main will handle passing data around, telling the networker to send specific messages or changes, passing the returned XML to the parser, and then passing the parsed values to UI for handling.
I'm curious though for advice beyond that.
Have a look at creating a service that is created with your Activity. Without knowing the details of your plan, a Service looks like the optimal solution to perform all the heavy work.
UPDATE:
You could have the calls to web API run in a Service and, when needed, update the UI through an interface. You would have to instruct the Service to run on its own thread, so thread safety is an issue, but less trouble in the long run than using an AsyncTask.
Have a thought about using Google C2DM.
In your case,
Pros -> Less battery use, coordinated network traffic, Don't have to run a continues service and doesn't have the potential of being killed when the device runs out of resources.
Cons -> You have to post the results manually back to your internal server, and server should know which request the device is replying to. Communication is disconnected and may not be real-time. Requires a google account on the device and Google market.
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.
When as a developer I should feel I need to have a separate process for a Android component/s?
Does introducing a new process has any side effect on application's overall performance?
Any other info is greatly appreciated.
Thanks,
SKU
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.
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.
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 ;)
I've just recently started working with the android framework and am looking for advice/design patterns to use for the following situation:
Application is a server/client structure. The server should be running at all times (or at least be recreated shortly after termination), but the client can close as need be. To accomplish the server, I understand that I want to extend Service and use START_STICKY functionality and run it in the background.
The part where I'm a bit lost of how to proceed is that I want to create several persistent network connections inside the server. It is important that the connections are threaded and can run asynchronously. A lot of documents point towards using AsyncTask for this, but I don't need to reference the UI thread at all from the network threads and the connections wont ever be terminated, so I'm hoping someone could point me in a better direction?
My conceptual idea was to have the network threads bind to the service to store events, and the client can then also bind to the service to retrieve the events. I'm unsure of the structure to use for these network threads.
The server should be running at all times
There are very very few applications that need this. Statistically speaking, yours probably isn't one of them. Users attack people like you with task killers and the like, plus give out one-star ratings on the Market for harming their use of their device. I strongly encourage you to reconsider this design decision.
so I'm hoping someone could point me in a better direction?
Plain old ordinary Java threads are just fine. Depending on the nature of the threads, you might consider using a thread pool. This part is not significantly different than in other Java environments. Bear in mind that the vast majority of Android devices today are single-core, and you only have so much heap space (as little as 16MB), so having tons o' threads isn't exactly great.
My conceptual idea was to have the network threads bind to the service to store events
The network threads are part of the service, and therefore don't need to bind to it.