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path: root/indra/llcommon/chrono.h
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2021-10-05SL-16024: Add ThreadSafeSchedule, a timestamped LLThreadSafeQueue.Nat Goodspeed
ThreadSafeSchedule orders its items by timestamp, which can be passed either implicitly or explicitly. The timestamp specifies earliest delivery time: an item cannot be popped until that time. Add initial tests. Tweak the LLThreadSafeQueue base class to support ThreadSafeSchedule: introduce virtual canPop() method to report whether the current head item is available to pop. The base class unconditionally says yes, ThreadSafeSchedule says it depends on whether its timestamp is still in the future. This replaces the protected pop_() overload accepting a predicate. Rather than explicitly passing a predicate through a couple levels of function call, use canPop() at the level it matters. Runtime behavior that varies depending on an object's leaf class is what virtual functions were invented for. Give pop_() a three-state enum return so pop() can distinguish between "closed and empty" (throws exception) versus "closed, not yet drained because we're not yet ready to pop the head item" (waits). Also break out protected tryPopUntil_() method, the body logic of tryPopUntil(). The public method locks the data structure, the protected method requires that its caller has already done so. Add chrono.h with a more full-featured LL::time_point_cast() function than the one found in <chrono>, which only converts between time_point durations, not between time_points based on different clocks.