AuroraRuntime/Include/Aurora/Threading/WakeOnAddress.hpp

/***
    Copyright (C) 2023 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: WakeOnAddress.hpp
    Date: 2023-3-11
    Author: Reece
    Note: In emulation mode (*):
              1: Wakes occur in FIFO order
              2: uWordSize can be any length not exceeding 32 bytes
          otherwise
              1: Wakes are orderless
              2: uWordSize must be less than or equal to 8 bytes
              3: only the least significant 32bits are guaranteed to be used as wake signals
          in either mode:
              1: WaitOnAddress[...] can wake at any-time if a fast path permits.
                 (we only care about strict guarantees during the deep slow-path yield operation. 
                  after the first pass, after a cache miss, after a fast path succeeds,
                  it's anybodys guess who will *return* first. on the other hand, a set of 5 threads 
                  already in the kernel *should* wake in the expected order. otherwise, WaitOnAddress[...]
                  just assumes pTargetAddress != pCompareAddress is an orderless return condition.)
           
          * By default: UNIXes and targets below/inc Windows 7 will be in userland emulation mode for performance reasons.
          *             Linux and other targets can directly interface with their futex interface under a smaller wrapper;
          *             however, these applications are limited to internal synchronization primitives. The added bloat 
          *             of the WaitOnAddress/FUTEX/atomic wait emulation layer improves performance in real world dumb
          *             code with spurious wakes, odd word sizes, and pointer alignments. Not to mention some targets 
          *             are stuck with semaphores or condition variables to start off with, and therefore need this
          *             for the sake of porting modern applications. The aforementioned synchronization primitives
          *             are written with OS specific optimizations in mind, and therefore consider emulation bloat.
          *             bPreferEmulatedWakeOnAddress disables the emulation layer, if theres a reasonable native 
          *             interfaces available.
          * Defer to ThreadingConfig::bPreferEmulatedWakeOnAddress = !AuBuild::kIsNtDerived 
***/
#pragma once

namespace Aurora::Threading
{
    AUKN_SYM void WakeAllOnAddress(const void *pTargetAddress);

    AUKN_SYM void WakeOnAddress(const void *pTargetAddress);

    // WakeAllOnAddress with a uNMaximumThreads which may or may not be respected
    AUKN_SYM void WakeNOnAddress(const void *pTargetAddress,
                                 AuUInt8 uNMaximumThreads);

    // On systems with processors of shared execution pipelines, these try-series of operations will spin (eg: mm_pause) for a configurable 
    //  amount of time, so long as the the process-wide state isn't overly contested. This means you can use these arbitrarily without 
    //  worrying about an accidental thundering mm_pause herd. If you wish to call WaitOnAddress[...] afterwards, you should report you already
    //  spun via optAlreadySpun. If the application is configured to spin later on, this hint may be used to prevent a double spin.
    AUKN_SYM bool TryWaitOnAddress(const void *pTargetAddress,
                                   const void *pCompareAddress,
                                   AuUInt8 uWordSize);

    // On systems with processors of shared execution pipelines, these try-series of operations will spin (eg: mm_pause) for a configurable 
    //  amount of time, so long as the the process-wide state isn't overly contested. This means you can use these arbitrarily without 
    //  worrying about an accidental thundering mm_pause herd. If you wish to call WaitOnAddress[...] afterwards, you should report you already
    //  spun via optAlreadySpun. If the application is configured to spin later on, this hint may be used to prevent a double spin.
    //  In the case of a pTargetAddress != pCompareAddress condition, the optional check parameter is used to verify the wake condition.
    //  Otherwise, spinning will continue.
    AUKN_SYM bool TryWaitOnAddressEx(const void *pTargetAddress,
                                     const void *pCompareAddress,
                                     AuUInt8 uWordSize,
                                     const AuFunction<bool(const void *, const void *, AuUInt8)> &check);

    // Relative timeout variant of nanosecond resolution WoA. 0 = indefinite
    AUKN_SYM bool WaitOnAddress(const void *pTargetAddress,
                                const void *pCompareAddress,
                                AuUInt8 uWordSize,
                                AuUInt64 qwNanoseconds,
                                AuOptional<bool> optAlreadySpun = {} /*hint: do not spin before switching. subject to global config.*/);

    // Absolute timeout variant of nanosecond resolution WoA. Nanoseconds are in steady clock time. 0 = indefinite
    AUKN_SYM bool WaitOnAddressSteady(const void *pTargetAddress,
                                      const void *pCompareAddress,
                                      AuUInt8 uWordSize,
                                      AuUInt64 qwNanoseconds,
                                      AuOptional<bool> optAlreadySpun = {} /*hint: do not spin before switching. subject to global config.*/);
}