Package inflight provides primitives(data strutures) for managing inflight operations that are being processed in a distributed system. CallGroup spawns off a group of operations for each call to Add() and calls the CallGroupCompletion func when the last operation have completed. The CallGroupCompletion func can be thought of as a finalizer where one can gather errors and/or results from the function calls. OpQueue is a thread-safe duplicate operation suppression queue, that combines duplicate operations (queue entires) into sets that will be dequeued togather.