How much performance does it costs to broadcast intents?
Is it okay to broadcast multiple per second or are intents expensive?
Intents are meant to launch different activities within the Android OS or to inform about basic actions. It seems like a bad design pattern to use them otherwise. As they travel between different processes and therefore implement the Parcelable interface, they are not the most light-weight.
If you are looking to update different activities at the same time you might consider using a common service.
According to this blog post, intents are 10 times slower than direct function calls
http://andytsui.wordpress.com/2010/09/14/android-intent-performance/
It doesn't cost THAT much, but think of it the same way as you would a broadcast in a network environment. If you want to continually send a message to a device, you wouldn't send broadcasts every 100ms. That would just flood the network. Sending a broadcast once every, say, 10 seconds might be appropriate though.
What exactly the best implementation is entirely depends on what you're doing. In certain circumstances, if you have several services running that need to be run independently, and you're only broadcasting these intents that fast for say, 10 or 15 seconds. That might be ok.
But we can't really say.
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)
Firstly I may say that I know there are a lot of resources dealing with the communication between services and activities, I have also read the service-related part of the android developer guide. However, I'm still not sure about the best approach in my case.
When it comes to the communication between services and other components (like activities), bound services are described as the solution in most cases. But from my unterstanding, the use of a bound service always results in a request/response-model - an activity invokes a method on the service (request) and gets a return value (response). The android dev guide calls this a client/server-model.
In my scenario, a service generates a list of POJOs on a regular basis, but not exactly predictable (let's say every 1.5 - 2 seconds). Every time this happens, the list should be transferred to an activity in order to display it on the screen. In my opinion, a bound service is not the solution here, since my scenario does not match the request/response-model. In fact, the activity is passive and not really aware of the service. Of course I could use a polling strategy together with a bound service, but imho this is not the best approach in my case.
What would you recommend? I found solutions using a BroadcastReceiver in the activity (the service acts as sender), is this the only way or are there any other approaches? Or do I have a wrong unterstanding of bound services and they are not limited to request/response-scenarios?
edit:
As I already mentioned, a new list (java.util) is generated every 1.5-2 seconds by the service and should immediately passed to the activity. Such a list contains 20-25 POJOs that represent model objects; they contain 5 Strings and 3 integers each.
Just to give you a feeling of the complexity.
Is the BroadcastReceiver adequate for this amount of data and frequency?
I would say, BroadcastReceiver is the best approach for this as compare to other options like handler, it would be create problem when large amount of calls would be occur. BroadcastReceiver will work fine because the flow of its working. I have worked with this, and I have got good result.
Has anyone really used this? I am so in the habit of registering/unregistering my BroadcastReceivers inside an Activity that I almost stuttered when I saw this. Does this keep all my Broadcasts to my specific Linux Process ID that my app is running on? My Actions and Extras are package specific and the ones that are not are meant to be that way to allow other applications to possibly pick up an intent. I can see one easy use, I just did a test case with an AsyncTask, ProgressDialog, and an Activity. But what is the purpose? Is this for security? I am not a linux guru and was hoping for some input.
Per the LocalBroadcastManager documentation, the advantages are:
You know that the data you are broadcasting won't leave your app, so don't need to worry about leaking private data.
It is not possible for other applications to send these broadcasts to your app, so you don't need to worry about having security holes they can exploit.
It is more efficient than sending a global broadcast through the system.
You can also take a look at the LocalBroadcastManager source if you'd like to determine exactly how it works.
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 can find several examples of how to build a service, but I'm having a difficult time finding a working example of how to send messages between an Activity and a Service. From what I can find, I think my options are to use Intents, AIDL, or to use the service object itself as per this question.
In my case, my activity is the only activity that will ever access the service, so a local service will do. When the activity is open, I want to see some status messages from the service, which will be coming in at up to 20 Hz. Are there any limitations on how many messages per second those communications methods will support? Basically, which method is going to be best for my situation?
Thanks.
Since your Actvity and Service are a part of the same app, then no need to use AIDL. You may simply use your Service as a local one.
The limitation is only affected by the performance of your device. There is no cap on requests per second.
Usually there is a context switch involved, that uses quite a lot of cpu (compared to other parts of the transmission), but since you use a local service you don't suffer from that. In any case, 20Hz is not a problem.
The best solution for you would be to use AIDL, and set up a callback that the service can call to report its status.
There is good example of how this is done in the APIDemos.