Blockage

A blockage is like a semaphore or lock. A blockage can be used to block (suspend) other entities while they wait for the blockage to be cleared. The user can mark process code with the start of a blockage and a subsequent end of the blockage. While the entity that creates the blockage is within the blocking code, other entities can be made to wait until the blockage is cleared. Only the entity that creates the blockage can start and clear it. A started blockage must be cleared before the end of the process routine that contains it; otherwise, an exception will occur. Thus, blockages that are started must always be cleared. The primary purpose of this construct is to facilitate process interaction between entities. Using blockages should be preferred over raw suspend/resume usage and even the use of Suspension instances.