Apple resolved this issue with the introduction of multitasking operating system iOS 4.With Multitasking, you can use more than one app at a time on your iOS device.
The system handles those background Apps easily and sends them into suspended state after few minutes of inactivity.
In case of suspended state , User has nothing to do with that App. But,if the user wants to open the same application again,it will start from the same stage,where he left it.
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In this case,user can't resume the whole process again.But from developer's side,it can be accomplished by using Apple's background execution of tasks for finite-lengthy time.
iOS system can terminate the App in background anytime,if it gets low memory issue.