/** * Footnotes: * "Wakes the count of currently sleeping threads without guaranteed respect for ordering." * "Assuming correctness of your mutex paths, this will wake all threads up-to your everyone-be-alert condition" * [...] * "Schedules a single thread for wake up without guaranteed respect for ordering. * * A simple explaination: *--------------------------------------------- * Problematic broadcasts: * * Under mutex: * Sleep: [A, B, C] * * Under or out of mutex (it doesnt matter so long as you barrier the mutex after the state change): * ~awake all? shutdown condition? who knows~ * Broadcast * * Out of mutex (Bad Use Case !!!): * if (~missed/incorrect if !work available check before sleep~) * Sleep: [D] * // given that WaitForSignal forces you to unlock and relock a mutex, this illogical branch should never happen * * Effect: * Awake: [B, C, D] * Sleeping: [A] * *--------------------------------------------- * Problematic signals: * * Under mutex: * Sleep: [A, B, C] * * Not under mutex (it doesnt matter so long as you barrier the mutex after the state change): * Signal * * Under mutex: * Sleep: [D] * * Effect: * Awake: [D] * Sleeping: [A, B, C] * *--------------------------------------------- * Cause: * The condition variables account for the amount of threads sleeping accuarely, not the order. * This is usually a good thing because ordering under a spinloop generally does not happen in time and/or does not matter. * The lowest common denominator of kernel thread scheduling is fundamentally that of a semaphore scheduled with respect to buckets of integer thread priority levels, and nothing more complex than that. * To implement ordering, is to implement cache-thrashing and increased context-switching for an abstract idea of "correctness" that doesn't apply to real code or performance goals. * (spoilers: using a condvar, your work pool of uniform priorities couldn't care less which thread wakes up first, nor does a single waiter pattern; but your end product will certainly bleed performance with ticket yield thrashing or suboptimal spinning ) * ( : the same can be said for semaphores; what part of waiting while an available work count is not zero needs ordering? ) * ( : yield thrashing, that might i add, serves no purpose other than to get the right thread local context and decoupled-from-parent thread id of a context on a given physical core of a highly limited set ) * ( : the only valid use case for ordered lock types is in the instance of RWLock read exhausting writers, and thats easily accounted by separating the read and write wake queues ) * *--------------------------------------------- * The fix[es] / Mitigations: * * Ensure to check the correctness of the sleep condition, and that the mutex is properly locked, before calling any Aurora condition primitives' sleep routines * (why the fuck would you be sleeping on a variable state observer without checking its' state, causing an unwanted defect? this is counter to the purpose of using a condvar.) * * * Increase the size of the condition variable to account for a counter and implement inefficient rescheduling, to fix fundamentally flawed user code * (no thanks. implement ticket primitives yourself, see: the hacky workaround.) * * * "Problematic signals:" I know what you're trying to do, and you're being stupid for attempting to force condvars to act as barriers this way. Instead, just use the actual timeline-capable semaphore of AuFutexSemaphore::LockUntilAtleastAbsNS and bPreferEmulatedWakeOnAddress = true. *--------------------------------------------- * The hacky workaround: * * If you can somehow justify this, i doubt it, but if you can, you can aim for the slow-path ordered sleep of/by using AuFutex[Mutex/Semaphore/Cond] with ThreadingConfig::bPreferEmulatedWakeOnAddress = true. * * Noting that all futex paths can still take a fast path to bypass ordering. */