Requests an initial allocation of virtual processor roots. Every virtual processor root represents the ability to execute one thread that can perform work for the scheduler.
virtual IExecutionResource * RequestInitialVirtualProcessors( bool doSubscribeCurrentThread ) =0;
Before a scheduler executes any work, it should use this method to request virtual processor roots from the Resource Manager. The Resource Manager will access the scheduler's policy using IScheduler::GetPolicy and use the values for the policy keys MinConcurrency, MaxConcurrency and TargetOversubscriptionFactor to determine how many hardware threads to assign to the scheduler initially and how many virtual processor roots to create for every hardware thread. For more information on how scheduler policies are used to determine a scheduler's initial allocation, see PolicyElementKey.
The Resource Manager grants resources to a scheduler by calling the method IScheduler::AddVirtualProcessors with a list of virtual processor roots. The method is invoked as a callback into the scheduler before this method returns.
If the scheduler requested subscription for the current thread by setting the parameter doSubscribeCurrentThread to true, the method returns an IExecutionResource interface. The subscription must be terminated at a later point by using the IExecutionResource::Remove method.
When determining which hardware threads are selected, the Resource Manager will attempt to optimize for processor node affinity. If subscription is requested for the current thread, it is an indication that the current thread intends to participate in the work assigned to this scheduler. In such a case, the allocated virtual processors roots are located on the processor node the current thread is executing on, if possible.
The act of subscribing a thread increases the subscription level of the underlying hardware thread by one. The subscription level is reduced by one when the subscription is terminated. For more information on subscription levels, see IExecutionResource::CurrentSubscriptionLevel.