The component lifecycle

Reference | Component Container

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Granitic is responsible for creating the Go structs that you tell it manage as components. By default, this means that Granitic will create a new instance of the struct (using new()). The instance will remain in memory until your application shuts down.

If you want to take advantage of it, Granitic supports a more sophisticated lifecycle management pattern that your components can opt-in to by implementing one or more of the interfaces provided in Granitic’s IoC package

Start

If your component implements ioc.Startable, it’s StartComponent() method will be called once Granitic has finished instantiating and configuring all components.

This method is a good place to put any initialisation code. Any errors returned by a StartComponent() method will prevent your application from starting.

Allow access

Components that allow inbound communication (via web services, queues or some other) are encouraged to implement ioc.Accessible. The AllowAccess() method on components implementing ioc.Accessible is called after all components have their StartComponent() methods invoked.

This allows you to make sure that all components in your application have started correctly and are ready before opening ports into the application. This technique is employed by Granitic’s HTTPServer facility

Any errors returned by an AllowAccess() method will prevent your application from starting.

Blocking the allow access phase

If your component implements ioc.AccessibilityBlocker, it cam prevent Granitic moving from the ‘start’ phase to the ‘allow access’ phase for all components.

This can be useful if your component has spawned a goroutine to perform some sort of initialisation in it’s StartComponent() method. For example, the component might be registering your application with a service discovery manager or an external logger.

If your component’s BlockAccess() method returns true, Granitic will not progress to the allow access phase. The number of times this method will be called and the interval between checks in controlled through the ‘system’ facility.

Id BlockAccess() returns an error, your application will not start.

Suspend and resume

Components that want to be able to stop or interrupt their behaviour in reaction to the entire application being ‘suspended’ should implement ioc.Suspendable.

The Suspend() method will be called when the application receives a suspend command through runtime control and Resume() will be called when a resume command is received.

Errors returned by these methods will be logged, but do not cause the application to exit.

Stopping

Components that need to perform cleanup, finish work or safely dispose of resources should implement ioc.Stoppable. This requires your component to implement three methods.

PrepareToStop()

PrepareToStop() is a warning that a stop signal is imminent. This is your component’s opportunity to prevent any new work being started (by closing ports, interrupting jobs etc.). This method should return immediately as ReadyToStop() is your component’s opportunity to delay shutdown.

ReadyToStop()

ReadyToStop() allows your component to say whether it is now ready for the application to shut down. Any errors returned will be logged but will not cause the application to exit.

The number of times an individual component can say that it is not ready before the application shuts down anyway are controlled though the ‘system’ facility.

Stop()

This is the instruction from Granitic to stop all work immediately. It is your component’s last chance to try and cleanly stop work or free up resources.

Component state

If your application wants to keep track of it’s current lifecycle state it can use the pre-defined ioc.ComponentState enumeration. This is purely a convenience for your component - the values are not read or set by the framework.

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