Higher-order conditional synchronization
Benjamin Goldberg, Niki Afshartous · 1999
Conditional synchronization—a mechanism that conditionally blocks a thread based on the value of a boolean expression currently exists in several programming languages. We propose promoting conditional synchronization to first-class status allowing the synchronization object representing a suspended conditional synchronization to be passed as a value. To demonstrate our idea we extend Concurrent ML and present several examples illustrating the expressiveness of first-class conditional synchronization (FCS). FCS has broadcast semantics making it appropriate for applications such as barriers and discrete-event simulation. The semantics also guarantee that no transient store configurations are missed. The end result facilitates abstraction and adds flexibility in writing concurrent programs. To minimize re-evaluation of synchronization conditions we propose a static analysis and translation that identifies expressions for the run-time system that could affect the value of a synchronization condition. The static analysis (which is based on an effect type system) therefore precludes excessive run-time system polling of synchronization conditions.