AuroraRuntime/Media/Condvar and other reodering of thread primitives.txt

    /**
     * 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.
     */