Common Design Patterns for Symbian OS: The Foundations of Smartphone Software

3.1. Immortal

Intent

Allocate a resource as soon as possible so that, when you come to use it later, it is guaranteed to be both available and quickly accessible.

AKA

Static Allocation, Pre-allocation, Fixed Allocation [Weir and Noble, 2000]

3.1.1. Problem

3.1.1.1. Context

A resource is required and the details of how it will be used are well understood. There is a critical need for its allocation, as well as the possible failure of the allocation, to be controlled.

3.1.1.2. Summary

You need to resolve one or more of the following:

• You would like to guarantee that allocating the resource will succeed.

• The responsiveness of your application or service is negatively impacted by the time to allocate one or more resources.

• You need to avoid any unbounded resource allocations during a real-time use case.

Whichever of the above applies in your situation, it must also be more important that your application or service always has access to the resource than it is to share the resource with other potential resource clients.

3.1.1.3. Description

On most mobile devices, some applications or services are considered essential. What is essential may be mandated by the mobile device creator (e.g. a large-mega-pixel camera, if it is an essential selling point for a specific device) or by regulatory bodies (e.g. the ability to make a call to the emergency services). In all normal situations, an essential service should not fail.^[] Hence these services should ensure that all the possible resources ...