Pointer to a critical section that is used to serialize state changes.
This variable is initialized in the class constructor; see CBaseFilter::CBaseFilter.
Hold this critical section during state transitions, or when a method accesses the state over several operations. The base class holds the critical section in the following methods:
Do not hold this critical section during streaming operations (that is, when delivering samples to a downstream filter). Serialize streaming operations using a different critical section. Otherwise, it can cause deadlock.