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#pragma once
namespace Whisper
{
// A callback to offload to the thread pool
using pfnParallelForCallback = HRESULT( * )( int ith, void* ctx ) noexcept;
// A simple parallel for implementation; Windows includes a decent thread pool since Vista (2006)
HRESULT parallelFor( pfnParallelForCallback pfn, int threadsCount, void* ctx );
// Use this version when you wanna use the thread pool repeatedly, for the same work.
// This class caches native work handle, saving a couple of WinAPI calls.
class alignas( 64 ) ThreadPoolWork
{
PTP_WORK work = nullptr;
// We want these volatile fields in another cache line from the rest of the data of this class.
// threadIndex field is concurrently modified by different CPU cores, and these cache coherency protocols are slow.
// OTOH, work and callback fields of this class only change when created / destroyed, that cache line is shared by CPU cores without any performance penalty.
alignas( 64 ) volatile long threadIndex = 0;
volatile HRESULT status = E_UNEXPECTED;
static void __stdcall callbackStatic( PTP_CALLBACK_INSTANCE Instance, PVOID pv, PTP_WORK Work );
protected:
virtual HRESULT threadPoolCallback( int ith ) noexcept = 0;
public:
ThreadPoolWork() = default;
ThreadPoolWork( const ThreadPoolWork& ) = delete;
~ThreadPoolWork();
HRESULT create();
HRESULT parallelFor( int threadsCount ) noexcept;
};
}
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