|411||411||Since thunk evaluation and blackholing is a critical for good performance, we would like the common case - thunk finishes evaluation without being blackholed - to be fast. Hence, we retain the RTS messaging layer between the capabilities for blocking on a blackhole. When a thread enters a blackhole whose owner thread resides on another capability, a block request message is sent to the corresponding capability. Notice that the [#SContAffinity association] between SConts (threads) and capabilities is essential for identifying which capability to send the block request message to. During every iteration of the RTS Schedule loop, a capability checks its inbox for pending messages, and if any, processes the messages. Hence, no synchronization is necessary for replacing a thunk with a value.