Loosen up locking behavior of GetRegistration

[dotnetjunkie]

As described in #862, Simple Injector is very strict in locking the Container when calling GetRegistration. The current behavior is to "lock the container in all cases except when an explicitly made registration can be returned." This means that in the following cases, the container will lock:

• When the requested registration is resolved using unregistered type resolution
• When the requested registration is a DependencyMetadata<T>
• When the requested registration is a collection
• When the requested registration is a concrete unregistered type, and ResolveUnregisteredConcreteTypes is set.
• When the requested registration can't be found.

There are cases where a call to GetRegistration should certainly cause the container to be locked, such as when the underlying code triggers a call to Container.GetInstance, GetService, or GetAllInstances, or BuildExpression. For instance, an unregistered type resolution event might do this.

But for GetRegistration itself, it could itself leave the container unlocked.

Not locking the container has become extra important in v5, because locking the container now, by default, triggers verification. This means that a call to GetRegistration causes the verification, which can be confusing. It also disallows the use of GetRegistration to make decide what and how to register.

Tasks:

• Remove the call to LockContainer from the GetRegistration method.
• Check the XML docs for all GetRegistration method to see if they are up to date, and if not update them.

[dotnetjunkie]

feature-863 branch created.

[dotnetjunkie]

After doing some more research, I found that the unit tests do a good job in explaining what can happen when GetRegistration does not lock the container:

Whenever a not-explicitly made registration can be returned using unregistered type resolution, the container needs to be locked, changing the container might invalidate the registration. For instance, adding unregistered type resolution events later, might cause a different registration to be returned when GetRegistration is called again.

This means that the locking behavior can't be fully removed. Still, I feel that it's okay to loosen the behavior and only lock when the registration is made implicitly.