XPCOM Code FAQ

What are the Global Objects that XPCOM maintains

mGlobalServiceManager
mGlobalComponentManager

What are the static classes that XPCOM maintains

nsComponentManager
nsServiceManager

Is there any restriction on which static class I should call first

No restrictions. You can call any function from the static classes nsComponentManager and nsServiceManager. XPCOM will do the right thing to initialize itself at both places.

Autoregistration() can happen only after Init_XPCOM() is called since the registy might be required by SelfRegister() functions of the dlls and it is only in Init_XPCOM() do we create register the RegistryFactory() with the ComponentManager.

What is the order of creation of the ServiceManager, ComponentManager and Registry

Init_XPCOM()

create the global component manager

create the global component manager and register as service with the global service manager

RegisterFactory(...RegistryFactory...)  Register the RegistryFactory() with the component manager so that new registry objects can be created.

Now the hard problem is when to trigger Init_XPCOM() There are two static objects nsComponentManager and nsServiceManager. Any function in either of them can be called first. Today nsServiceManager::GetService() is the first one that gets called. All the members of the static nsServiceManager use the nsGetGlobalServiceManager() to get to the global service manager. All members of the static nsComponentManager use the nsGetGlobalComponentManager() to get to the global component manager. Hence if we trigger Init_XPCOM() from both NS_GetGlobalComponentManager() and NS_GetGlobalServiceManager() we will be safe.

Is there a global Registry being maintained

No. The nsIRegistry is designed to be lightweight access to the registry. Consumers who need to access the registry should use the component manager to create the their own registry access object. This is required because the open() call is supported by the nsIRegistry() and if we maintain a global registry arbitrating which registry file is opened is going to be a major headach.

The ProgID for the registry will be component://netscape/registry