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Binders are used for Inter(not intra) Process Communication/Remote Method Invocation so why/how the communication between Activity and Service is possible via binders where there are no different processes involvement.

When the very first component of an app is initialized a request to the kernal is triggeres (I think via ActivityManagerService(Native)-AMS > AMN) (running in system_process) for a new process fork if no corresponding process exists. Once the process is created then any other component (say a Service) belongs to the same process unless specified. Now this service wants to communicate to an Activity of the same process. Then why IBinder is one of the option?

Doesn't that violate the underlying principle on which Binders are created?

Sandeep Gupta
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Interprocess communication is done by writing data to some source such as a socket or pipe, and another process reading it. There's no reason that the same process can't read and write though- it's less efficient than other means of passing data within a process, but it still works.

As for why would you use it in the same process- the alternative would be for Android to have two ways of communicating with services, one way for if they're the same process, and one way for it they aren't. That would complicate things for the framework for minimal gain. It would greatly complicate things for Services where the client may or may not be in the same process (say a service that is used by both the client app and other apps by the same company). So they just use the same method for both.

Gabe Sechan
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Binders are intended to be a construct of an IPC - this is true but, if used in the same process to communicate between an Activity and a Service, there is no performance cost, i.e, it is converted into a direct call instead of an RPC.

Don't assume that Binders will only be used for IPC but it is a general purpose communication mechanism in Android.

You won't find this documented normally anywhere. I found it in one of the discussion between Commonsware and Dianne Hackborne(designer of the binder concept in the Android team).

Manish Kumar Sharma
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