IntentService has its own thread, starting another thread from handleIntent, the service considered live or completed service and doesn't matter another thread is active or nor?
and as soon as the IntentService completed its job ,is it possible to return to main thread and call another thread, but the start of the another thread could be from main thread not from activity, as the service could complete its job during any active activity.
IntentService has its own thread, starting another thread from
handleIntent
Don't ever do that. Once the IntentService's onHandleIntent() method returns, the service is destroyed and the process is likely to be killed as well. Android has no idea what threads you've started so for all it knows your process is idle and wasting resources.
If you need to "start" something else when the IntentService is done, use startActivity(), startService() or sendBroadcast() (whichever is appropriate). Again, Android doesn't know about your threads.
If you need procedure call semantics (e.g, start service, have it perform some task, then return control to the caller), IntentService isn't the right tool. Use a bound service (or bound AIDL service if you need to cross process boundaries).
I have a Service where I run a task inside a Thread. I call this Service many times and obviously it creates the corresponding number of Threads.
How am I going to know when no one Thread is running so I can call stopSelf() ?
The easiest thing to do is make your service subclass IntentService. This is a special kind of Service that will perform work in a background thread, and automatically stop the service when there is no more work to perform. There is a single thread per Service that you declare in your manifest. All you do is determine what sort of work you want to perform by implementing its onHandleIntent(), which is automatically run in that background thread for each Intent delivered to it.
You can keep track of the running threads in an array. When each thread completes it should remove itself from the array and call a method that checks if there are any running threads. That method just checks if the list of running threads is empty, and if so, calls stopSelf().
Or use IntentService if this suits your needs.
I am seeking an example of something that can be done with an IntentService that cannot be done with a Service (and vice-versa)?
I also believe that an IntentService runs in a different thread and a Service does not. So, as far as I can see, starting a service within its own thread is like starting an IntentService. Is that correct?
Tejas Lagvankar wrote a nice post about this subject.
Below are some key differences between Service and IntentService.
When to use?
The Service can be used in tasks with no UI, but shouldn't be too long. If you need to perform long tasks, you must use threads within Service.
The IntentService can be used in long tasks usually with no communication to Main Thread. If communication is required, can use Main Thread handler or broadcast intents. Another case of use is when callbacks are needed (Intent triggered tasks).
How to trigger?
The Service is triggered by calling method startService().
The IntentService is triggered using an Intent, it spawns a new worker thread and the method onHandleIntent() is called on this thread.
Triggered From
The Service and IntentService may be triggered from any thread, activity or other application component.
Runs On
The Service runs in background but it runs on the Main Thread of the application.
The IntentService runs on a separate worker thread.
Limitations / Drawbacks
The Service may block the Main Thread of the application.
The IntentService cannot run tasks in parallel. Hence all the consecutive intents will go into the message queue for the worker thread and will execute sequentially.
When to stop?
If you implement a Service, it is your responsibility to stop the service when its work is done, by calling stopSelf() or stopService(). (If you only want to provide binding, you don't need to implement this method).
The IntentService stops the service after all start requests have been handled, so you never have to call stopSelf().
If someone can show me an example of something that can be done with an IntentService and can not be done with a Service and the other way around.
By definition, that is impossible. IntentService is a subclass of Service, written in Java. Hence, anything an IntentService does, a Service could do, by including the relevant bits of code that IntentService uses.
Starting a service with its own thread is like starting an IntentService. Is it not?
The three primary features of an IntentService are:
the background thread
the automatic queuing of Intents delivered to onStartCommand(), so if one Intent is being processed by onHandleIntent() on the background thread, other commands queue up waiting their turn
the automatic shutdown of the IntentService, via a call to stopSelf(), once the queue is empty
Any and all of that could be implemented by a Service without extending IntentService.
Service
Invoke by startService()
Triggered from any Thread
Runs on Main Thread
May block main (UI) thread. Always use thread within service for long task
Once task has done, it is our responsibility to stop service by calling stopSelf() or stopService()
IntentService
It performs long task usually no communication with main thread if communication is needed then it is done by Handler or BroadcastReceiver
Invoke via Intent
Triggered from Main Thread
Runs on the separate thread
Can't run the task in parallel and multiple intents are Queued on the same worker thread.
Don't reinvent the wheel
IntentService extends Service class which clearly means that IntentService is intentionally made for same purpose.
So what is the purpose ?
`IntentService's purpose is to make our job easier to run background tasks without even worrying about
Creation of worker thread
Queuing the processing multiple-request one by one (Threading)
Destroying the Service
So NO, Service can do any task which an IntentService would do. If your requirements fall under the above-mentioned criteria, then you don't have to write those logics in the Service class.
So don't reinvent the wheel because IntentService is the invented wheel.
The "Main" difference
The Service runs on the UI thread while an IntentService runs on a
separate thread
When do you use IntentService?
When you want to perform multiple background tasks one by one which exists beyond the scope of an Activity then the IntentService is perfect.
How IntentService is made from Service
A normal service runs on the UI Thread(Any Android Component type runs on UI thread by default eg Activity, BroadcastReceiver, ContentProvider and Service). If you have to do some work that may take a while to complete then you have to create a thread. In the case of multiple requests, you will have to deal with synchronization.
IntentService is given some default implementation which does those tasks for you.
According to developer page
IntentService creates a Worker Thread
IntentService creates a Work Queue which sends request to onHandleIntent() method one by one
When there is no work then IntentService calls stopSelf() method
Provides default implementation for onBind() method which is null
Default implementation for onStartCommand() which sends Intent request to WorkQueue and eventually to onHandleIntent()
Adding points to the accepted answer:
See the usage of IntentService within Android API.
eg:
public class SimpleWakefulService extends IntentService {
public SimpleWakefulService() {
super("SimpleWakefulService");
}
#Override
protected void onHandleIntent(Intent intent) { ...}
To create an IntentService component for your app, define a class that extends IntentService, and within it, define a method that overrides onHandleIntent().
Also, see the source code of the IntentService, it's constructor and life cycle methods like onStartCommand...
#Override
public int More ...onStartCommand(Intent intent, int flags, int startId) {
onStart(intent, startId);
return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
}
Service together an AsyncTask is one of best approaches for many
use cases where the payload is not huge. or just create a class
extending IntentSerivce. From Android version 4.0 all network
operations should be in background process otherwise the application compile/build fails.
separate thread from the UI. The AsyncTask class provides one of the simplest ways to fire off a new task from the UI thread. For more discussion of this topic, see the blog post
from Android developers guide:
IntentService is a base class for Services that handle asynchronous requests (expressed as Intents) on demand. Clients send requests through startService(Intent) calls; the service is started as needed, handles each Intent, in turn, using a worker thread, and stops itself when it runs out of work.
Design pattern used in IntentService
:
This "work queue processor" pattern is commonly used to offload tasks from an application's main thread. The IntentService class exists to simplify this pattern and take care of the mechanics. To use it, extend IntentService and implement onHandleIntent(Intent). IntentService will receive the Intents, launch a worker thread, and stop the service as appropriate.
All requests are handled on a single worker thread -- they may take as long as necessary (and will not block the application's main loop), but only one request will be processed at a time.
The IntentService class provides a straightforward structure for running an operation on a single background thread. This allows it to handle long-running operations without affecting your user interface's responsiveness. Also, an IntentService isn't affected by most user interface lifecycle events, so it continues to run in circumstances that would shut down an AsyncTask.
An IntentService has a few limitations:
It can't interact directly with your user interface. To put its results in the UI, you have to send them to an Activity.
Work requests run sequentially. If an operation is running in an IntentService, and you send it another request, the request waits until the first operation is finished.
An operation running on an IntentService can't be interrupted.
However, in most cases
IntentService is the preferred way to simple background operations
**
Volley Library
There is the library called volley-library for developing android networking applications
The source code is available for the public in GitHub.
The android official documentation for Best practices for Background jobs:
helps better understand on intent service, thread, handler, service. and also Performing Network Operations
I'm sure you can find an extensive list of differences by simply googling something such as 'Android IntentService vs Service'
One of the more important differences per example is that IntentService ends itself once it's done.
Some examples (quickly made up) could be;
IntentService: If you want to download a bunch of images at the start of opening your app. It's a one-time process and can clean itself up once everything is downloaded.
Service: A Service which will constantly be used to communicate between your app and back-end with web API calls. Even if it is finished with its current task, you still want it to be around a few minutes later, for more communication.
IntentService
IntentService runs on its own thread.
It will stop itself when it's done. More like fire and forget.
Subsequent calls will be queued. Good for queuing calls.
You can also spin multiple threads within IntentServiceif you need to- You can achieve this using ThreadPoolExecutor.
I say this because many people asked me "why use IntentService since it doesn't support parallel execution".
IntentService is just a thread. You can do whatever you need inside it- Even spinning multiple threads. The only caveat is that IntentService finishes as soon as you spin those multiple threads. It doesn't wait for those threads to come back. You need to take care of this. So I recommend using ThreadPoolExecutor in those scenarios.
Good for Syncing, uploading etc …
Service
By Default Service runs on the main thread. You need to spin a worker thread to do your job.
You need to stop service explicitly.
I used it for a situation when you need to run stuff in the background even when you move away from your app and come back more for a Headless service.
Again you can run multiple threads if you need to.
Can be used for apps like music players.
You can always communicate back to your activity using BroadcastReceivers if you need to.
An IntentService is an extension of a Service that is made to ease the execution of a task that needs to be executed in background and in a seperated thread.
IntentService starts, create a thread and runs its task in the thread. once done, it cleans everything. Only one instance of a IntentService can run at the same time, several calls are enqueued.
It is very simple to use and very convenient for a lot of uses, for instance downloading stuff. But it has limitations that can make you want to use instead the more basic (not simple) Service.
For example, a service connected to a xmpp server and bound by activities cannot be simply done using an IntentService. You'll end up ignoring or overriding IntentService stuffs.
Android IntentService vs Service
1.Service
A Service is invoked using startService().
A Service can be invoked from any thread.
A Service runs background operations on the Main Thread of the
Application by default. Hence it can block your Application’s UI.
A Service invoked multiple times would create multiple instances.
A service needs to be stopped using stopSelf() or stopService().
Android service can run parallel operations.
2. IntentService
An IntentService is invoked using Intent.
An IntentService can in invoked from the Main thread only.
An IntentService creates a separate worker thread to run background
operations.
An IntentService invoked multiple times won’t create multiple
instances.
An IntentService automatically stops after the queue is completed. No
need to trigger stopService() or stopSelf().
In an IntentService, multiple intent calls are automatically Queued
and they would be executed sequentially.
An IntentService cannot run parallel operation like a Service.
Refer from Here
If someone can show me an example of something that you can be done with an IntentService and can not be done with a service and the other way around.
IntentService can not be used for Long Time Listening, Like for XMPP Listeners, its a single time operator, do the job and wave goodbye.
Also it has just one threadworker, but with a trick, you can use it as unlimited.
The Major Difference between a Service and an IntentService is described as follows:
Service :
1.A Service by default, runs on the application's main thread.(here no default worker thread is available).So the user needs to create a separate thread and do the required work in that thread.
2.Allows Multiple requests at a time.(Multi Threading)
IntentService :
1.Now, coming to IntentService, here a default worker thread is available to perform any operation. Note that - You need to implement onHandleIntent() method ,which receives the intent for each start request, where you can do the background work.
2.But it allows only one request at a time.
I have a lot of async tasks in my activity, and I need to override AsyncTask for every call to do it async.
Can I replace all the AsyncTasks with BoundService + AIDL or I need to do it only with AsyncTask?
Service run in background but still run in main thread (AKA. UI thread), you will get ANR exception. according to API here:
Most confusion about the Service class actually revolves around what it is not:
A Service is not a separate process. The Service object itself does not imply it is running in its own process; unless otherwise specified, it runs in the same process as the application it is part of.
A Service is not a thread. It is not a means itself to do work off of the main thread (to avoid Application Not Responding errors).
You can use service, but you still need implement your thread logic in either service or activity,if you want something run in a separate thread.
Service is a daemon, AsynkTask is background thread
I'm writing a Service that uses an AsyncTask to do some network operations. Let's say the doInBackground of the AsyncTask is taking a very long time, and while that's happening, resources get low and the operating system is shutting down the Service.
When does the AsyncTask get killed? Will the AsyncTask still be running when onDestroy is called, or will it happen afterwards, or am I responsible for shutting down the AsyncTask? I'm trying to make sure I do not have race conditions between the code in my onDestroy and the code in my doInBackground.
The AsyncTask will continue running until either you cancel it or the system destroys the process hosting it. The system doesn't know, per se, about your AsyncTask so its not going to do anything about it when shutting down the Service, it certainly doesn't know the Service created the AsyncTask.
Its very likely that after onDestroy is called that the application's process will be destroyed as well and so will the AsyncTask. However, the safest policy is to be proactive and cancel the AsyncTask in onDestroy.
A perhaps interesting side note is that requests queued for processing will be lost if the process dies before they are processed. As such, any operations sent to an AsyncTask that must be completed need to be written to a persistent task log so they can be reissued if not completed.