WindowsPlatformTLS.h

Go to the documentation of this file.

// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "GenericPlatform/GenericPlatformTLS.h"
#include "Windows/WindowsSystemIncludes.h"
 
#if WITH_EDITOR
 
#include "Misc/AssertionMacros.h"
 
// Custom cross-platform dynamic TLS implementation because we hit Windows TLS slot limit (1088). compile-time defined limits for the maximum
// number of TLS slots and the maximum number of threads that use TLS. No dynamic memory allocation. Lock-free.
// Getting and setting a slot value is fast but has an additional indirection compared with OS TLS.
// Memory footprint is (roughly): MaxSlots * 4B + MaxThreads * 4B + MaxSlots * MaxThreads * 8B
 
namespace WindowsPlatformTLS_Private
{
    inline constexpr uint32 MaxSlots = WINDOWS_MAX_NUM_TLS_SLOTS; // how many slots are available
    inline constexpr uint32 MaxThreads = WINDOWS_MAX_NUM_THREADS_WITH_TLS_SLOTS; // how many threads can use TLS
 
    // a single OS TLS slot that is used to store the thread storage
    CORE_API extern uint32 PrimarySlot;
 
    CORE_API void** AllocThreadStorage();
}
 
#endif
 
struct FWindowsPlatformTLS
    : public FGenericPlatformTLS
{
    static UE_FORCEINLINE_HINT uint32 GetCurrentThreadId(void)
    {
        return Windows::GetCurrentThreadId();
    }
 
#if WITH_EDITOR
    CORE_API static uint32 AllocTlsSlot();
#else
    UE_FORCEINLINE_HINT static uint32 AllocTlsSlot()
    {
        return Windows::TlsAlloc();
}
 
#endif
 
#if WITH_EDITOR
    CORE_API static void FreeTlsSlot(uint32 SlotIndex);
#else
    UE_FORCEINLINE_HINT static void FreeTlsSlot(uint32 SlotIndex)
    {
        Windows::TlsFree(SlotIndex);
    }
#endif
 
    static inline void SetTlsValue(uint32 SlotIndex, void* Value)
    {
#if WITH_EDITOR
        using namespace WindowsPlatformTLS_Private;
 
        checkf(SlotIndex < MaxSlots, TEXT("Invalid slot index %u"), SlotIndex);
 
        void** ThreadStorage = (void**)Windows::FlsGetValue(PrimarySlot);
        if (ThreadStorage == 0)
        {
            ThreadStorage = AllocThreadStorage();
        }
        ThreadStorage[SlotIndex] = Value;
#else
        Windows::TlsSetValue(SlotIndex, Value);
#endif
    }
 
    static inline void* GetTlsValue(uint32 SlotIndex)
    {
#if WITH_EDITOR
        using namespace WindowsPlatformTLS_Private;
 
        checkf(SlotIndex < MaxSlots, TEXT("Invalid slot index %u"), SlotIndex);
    
        void** ThreadStorage = (void**)Windows::FlsGetValue(PrimarySlot);
        return ThreadStorage ? ThreadStorage[SlotIndex] : nullptr;
#else
        return Windows::TlsGetValue(SlotIndex);
#endif
    }
};
 
 
typedef FWindowsPlatformTLS FPlatformTLS;