UnrealEngineUWP/Engine/Source/Developer/DerivedDataCache/Private/DerivedDataCache.cpp

// Copyright 1998-2017 Epic Games, Inc. All Rights Reserved.


#include "CoreMinimal.h"
#include "Misc/CommandLine.h"
#include "HAL/ThreadSafeCounter.h"
#include "Misc/ScopeLock.h"
#include "Stats/StatsMisc.h"
#include "Stats/Stats.h"
#include "Async/AsyncWork.h"
#include "Serialization/MemoryReader.h"
#include "Serialization/MemoryWriter.h"
#include "Modules/ModuleManager.h"

#include "DerivedDataCacheInterface.h"
#include "DerivedDataBackendInterface.h"
#include "DerivedDataPluginInterface.h"
#include "DDCCleanup.h"
#include "ProfilingDebugging/CookStats.h"

DEFINE_STAT(STAT_DDC_NumGets);
DEFINE_STAT(STAT_DDC_NumPuts);
DEFINE_STAT(STAT_DDC_NumBuilds);
DEFINE_STAT(STAT_DDC_NumExist);
DEFINE_STAT(STAT_DDC_SyncGetTime);
DEFINE_STAT(STAT_DDC_ASyncWaitTime);
DEFINE_STAT(STAT_DDC_PutTime);
DEFINE_STAT(STAT_DDC_SyncBuildTime);
DEFINE_STAT(STAT_DDC_ExistTime);

#if ENABLE_COOK_STATS
#include "DerivedDataCacheUsageStats.h"
namespace DerivedDataCacheCookStats
{
	FCookStatsManager::FAutoRegisterCallback RegisterCookStats([](FCookStatsManager::AddStatFuncRef AddStat)
	{
		TMap<FString, FDerivedDataCacheUsageStats> DDCStats;
		GetDerivedDataCacheRef().GatherUsageStats(DDCStats);
		{
			const FString StatName(TEXT("DDC.Usage"));
			for (const auto& UsageStatPair : DDCStats)
			{
				UsageStatPair.Value.LogStats(AddStat, StatName, UsageStatPair.Key);
			}
		}

		// Now lets add some summary data to that applies some crazy knowledge of how we set up our DDC. The goal 
		// is to print out the global hit rate, and the hit rate of the local and shared DDC.
		// This is done by adding up the total get/miss calls the root node receives.
		// Then we find the FileSystem nodes that correspond to the local and shared cache using some hacky logic to detect a "network drive".
		// If the DDC graph ever contains more than one local or remote filesystem, this will only find one of them.
		{
			TArray<FString, TInlineAllocator<20>> Keys;
			DDCStats.GenerateKeyArray(Keys);
			FString* RootKey = Keys.FindByPredicate([](const FString& Key) {return Key.StartsWith(TEXT(" 0:")); });
			// look for a Filesystem DDC that doesn't have a UNC path. Ugly, yeah, but we only cook on PC at the moment.
			FString* LocalDDCKey = Keys.FindByPredicate([](const FString& Key) {return Key.Contains(TEXT(": FileSystem.")) && !Key.Contains(TEXT("//")); });
			// look for a UNC path
			FString* SharedDDCKey = Keys.FindByPredicate([](const FString& Key) {return Key.Contains(TEXT(": FileSystem.//")); });
			if (RootKey)
			{
				const FDerivedDataCacheUsageStats& RootStats = DDCStats[*RootKey];
				int64 TotalGetHits =
					RootStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, true) +
					RootStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, false);
				int64 TotalGetMisses =
					RootStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Miss, FCookStats::CallStats::EStatType::Counter, true) +
					RootStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Miss, FCookStats::CallStats::EStatType::Counter, false);
				int64 TotalGets = TotalGetHits + TotalGetMisses;

				int64 LocalHits = 0;
				if (LocalDDCKey)
				{
					const FDerivedDataCacheUsageStats& LocalDDCStats = DDCStats[*LocalDDCKey];
					LocalHits =
						LocalDDCStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, true) +
						LocalDDCStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, false);
				}
				int64 SharedHits = 0;
				if (SharedDDCKey)
				{
					// The shared DDC is only queried if the local one misses (or there isn't one). So it's hit rate is technically 
					const FDerivedDataCacheUsageStats& SharedDDCStats = DDCStats[*SharedDDCKey];
					SharedHits =
						SharedDDCStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, true) +
						SharedDDCStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, false);
				}
				AddStat(TEXT("DDC.Summary"), FCookStatsManager::CreateKeyValueArray(
					TEXT("TotalGetHits"), TotalGetHits,
					TEXT("TotalGets"), TotalGets,
					TEXT("TotalHitPct"), (double)TotalGetHits / TotalGets,
					TEXT("LocalHitPct"), (double)LocalHits / TotalGets,
					TEXT("SharedHitPct"), (double)SharedHits / TotalGets,
					TEXT("OtherHitPct"), double(TotalGetHits - LocalHits - SharedHits) / TotalGets,
					TEXT("MissPct"), (double)TotalGetMisses / TotalGets
					));
			}
		}
	});
}
#endif

/** Whether we want to verify the DDC (pass in -VerifyDDC on the command line)*/
bool GVerifyDDC = false;

/**
 * Implementation of the derived data cache
 * This API is fully threadsafe
**/
class FDerivedDataCache : public FDerivedDataCacheInterface
{

	/** 
	 * Async worker that checks the cache backend and if that fails, calls the deriver to build the data and then puts the results to the cache
	**/
	friend class FBuildAsyncWorker;
	class FBuildAsyncWorker : public FNonAbandonableTask
	{
	public:
		/** 
		 * Constructor for async task 
		 * @param	InDataDeriver	plugin to produce cache key and in the event of a miss, return the data.
		 * @param	InCacheKey		Complete cache key for this data.
		**/
		FBuildAsyncWorker(FDerivedDataPluginInterface* InDataDeriver, const TCHAR* InCacheKey, bool bInSynchronousForStats)
		: bSuccess(false)
		, bSynchronousForStats(bInSynchronousForStats)
		, bDataWasBuilt(false)
		, DataDeriver(InDataDeriver)
		, CacheKey(InCacheKey)
		{
		}
		
		/** Async worker that checks the cache backend and if that fails, calls the deriver to build the data and then puts the results to the cache **/
		void DoWork()
		{
			const int32 NumBeforeDDC = Data.Num();
			bool bGetResult;
			{
				INC_DWORD_STAT(STAT_DDC_NumGets);
				STAT(double ThisTime = 0);
				{
					SCOPE_SECONDS_COUNTER(ThisTime);
					bGetResult = FDerivedDataBackend::Get().GetRoot().GetCachedData(*CacheKey, Data);
				}
				INC_FLOAT_STAT_BY(STAT_DDC_SyncGetTime, bSynchronousForStats ? (float)ThisTime : 0.0f);
			}
			if (bGetResult)
			{
				
				if(GVerifyDDC && DataDeriver && DataDeriver->IsDeterministic())
				{
					TArray<uint8> CmpData;
					DataDeriver->Build(CmpData);
					const int32 NumInDDC = Data.Num() - NumBeforeDDC;
					const int32 NumGenerated = CmpData.Num();
					
					bool bMatchesInSize = NumGenerated == NumInDDC;
					bool bDifferentMemory = true;
					if (bMatchesInSize)
					{
						bDifferentMemory = 0 != FMemory::Memcmp(CmpData.GetData(), &Data[NumBeforeDDC], NumGenerated);
					}

					if(!bMatchesInSize || bDifferentMemory)
					{
						FString ErrMsg = FString::Printf(TEXT("There is a mismatch between the DDC data and the generated data for plugin (%s) for asset (%s). BytesInDDC:%d, BytesGenerated:%d, bDifferentMemory:%d"), DataDeriver->GetPluginName(), *DataDeriver->GetDebugContextString(), NumInDDC, NumGenerated, bDifferentMemory);
						ensureMsgf(false, *ErrMsg);
						UE_LOG(LogDerivedDataCache, Error, TEXT("%s"), *ErrMsg );
					}
					
				}

				check(Data.Num());
				bSuccess = true;
				delete DataDeriver;
				DataDeriver = NULL;
			}
			else if (DataDeriver)
			{
				{
					INC_DWORD_STAT(STAT_DDC_NumBuilds);
					STAT(double ThisTime = 0);
					{
						SCOPE_SECONDS_COUNTER(ThisTime);
						bSuccess = DataDeriver->Build(Data);
						bDataWasBuilt = true;
					}
					INC_FLOAT_STAT_BY(STAT_DDC_SyncBuildTime, bSynchronousForStats ? (float)ThisTime : 0.0f);
				}
				delete DataDeriver;
				DataDeriver = NULL;
				if (bSuccess)
				{
					check(Data.Num());
					INC_DWORD_STAT(STAT_DDC_NumPuts);
					STAT(double ThisTime = 0);
					{
						SCOPE_SECONDS_COUNTER(ThisTime);
						FDerivedDataBackend::Get().GetRoot().PutCachedData(*CacheKey, Data, true);
					}
					INC_FLOAT_STAT_BY(STAT_DDC_PutTime, bSynchronousForStats ? (float)ThisTime : 0.0f);
				}
			}
			if (!bSuccess)
			{
				Data.Empty();
			}
			FDerivedDataBackend::Get().AddToAsyncCompletionCounter(-1);
		}

		FORCEINLINE TStatId GetStatId() const
		{
			RETURN_QUICK_DECLARE_CYCLE_STAT(FBuildAsyncWorker, STATGROUP_ThreadPoolAsyncTasks);
		}

		/** true in the case of a cache hit, otherwise the result of the deriver build call **/
		bool							bSuccess;
		/** true if we should record the timing **/
		bool							bSynchronousForStats;
		/** true if we had to build the data */
		bool							bDataWasBuilt;
		/** Data dervier we are operating on **/
		FDerivedDataPluginInterface*	DataDeriver;
		/** Cache key associated with this build **/
		FString							CacheKey;
		/** Data to return to caller, later **/
		TArray<uint8>					Data;
	};

public:

	/** Constructor, called once to cereate a singleton **/
	FDerivedDataCache()
		: CurrentHandle(19248) // we will skip some potential handles to catch errors
	{
		FDerivedDataBackend::Get(); // we need to make sure this starts before we all us to start

		GVerifyDDC = FParse::Param(FCommandLine::Get(), TEXT("VerifyDDC"));
	}

	/** Destructor, flushes all sync tasks **/
	~FDerivedDataCache()
	{
		FScopeLock ScopeLock(&SynchronizationObject);
		for (TMap<uint32,FAsyncTask<FBuildAsyncWorker>*>::TIterator It(PendingTasks); It; ++It)
		{
			It.Value()->EnsureCompletion();
			delete It.Value();
		}
		PendingTasks.Empty();
	}

	virtual bool GetSynchronous(FDerivedDataPluginInterface* DataDeriver, TArray<uint8>& OutData, bool* bDataWasBuilt = nullptr) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_GetSynchronous);
		check(DataDeriver);
		FString CacheKey = FDerivedDataCache::BuildCacheKey(DataDeriver);
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("GetSynchronous %s"), *CacheKey);
		FAsyncTask<FBuildAsyncWorker> PendingTask(DataDeriver, *CacheKey, true);
		AddToAsyncCompletionCounter(1);
		PendingTask.StartSynchronousTask();
		OutData = PendingTask.GetTask().Data;
		if (bDataWasBuilt)
		{
			*bDataWasBuilt = PendingTask.GetTask().bDataWasBuilt;
		}
		return PendingTask.GetTask().bSuccess;
	}

	virtual uint32 GetAsynchronous(FDerivedDataPluginInterface* DataDeriver) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_GetAsynchronous);
		FScopeLock ScopeLock(&SynchronizationObject);
		uint32 Handle = NextHandle();
		FString CacheKey = FDerivedDataCache::BuildCacheKey(DataDeriver);
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("GetAsynchronous %s"), *CacheKey);
		bool bSync = !DataDeriver->IsBuildThreadsafe();
		FAsyncTask<FBuildAsyncWorker>* AsyncTask = new FAsyncTask<FBuildAsyncWorker>(DataDeriver, *CacheKey, bSync);
		check(!PendingTasks.Contains(Handle));
		PendingTasks.Add(Handle,AsyncTask);
		AddToAsyncCompletionCounter(1);
		if (!bSync)
		{
			AsyncTask->StartBackgroundTask();
		}
		else
		{
			AsyncTask->StartSynchronousTask();
		}
		// Must return a valid handle
		check(Handle != 0);
		return Handle;
	}

	virtual bool PollAsynchronousCompletion(uint32 Handle) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_PollAsynchronousCompletion);
		FAsyncTask<FBuildAsyncWorker>* AsyncTask = NULL;
		{
			FScopeLock ScopeLock(&SynchronizationObject);
			AsyncTask = PendingTasks.FindRef(Handle);
		}
		check(AsyncTask);
		return AsyncTask->IsDone();
	}

	virtual void WaitAsynchronousCompletion(uint32 Handle) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_WaitAsynchronousCompletion);
		STAT(double ThisTime = 0);
		{
			SCOPE_SECONDS_COUNTER(ThisTime);
			FAsyncTask<FBuildAsyncWorker>* AsyncTask = NULL;
			{
				FScopeLock ScopeLock(&SynchronizationObject);
				AsyncTask = PendingTasks.FindRef(Handle);
			}
			check(AsyncTask);
			AsyncTask->EnsureCompletion();
		}
		INC_FLOAT_STAT_BY(STAT_DDC_ASyncWaitTime,(float)ThisTime);
	}

	virtual bool GetAsynchronousResults(uint32 Handle, TArray<uint8>& OutData, bool* bDataWasBuilt = nullptr) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_GetAsynchronousResults);
		FAsyncTask<FBuildAsyncWorker>* AsyncTask = NULL;
		{
			FScopeLock ScopeLock(&SynchronizationObject);
			PendingTasks.RemoveAndCopyValue(Handle,AsyncTask);
		}
		check(AsyncTask);
		if (bDataWasBuilt)
		{
			*bDataWasBuilt = AsyncTask->GetTask().bDataWasBuilt;
		}
		if (!AsyncTask->GetTask().bSuccess)
		{
			delete AsyncTask;
			return false;
		}
		OutData = MoveTemp(AsyncTask->GetTask().Data);
		delete AsyncTask;
		check(OutData.Num());
		return true;
	}

	virtual IDerivedDataRollup* StartRollup() override
	{
		return NULL;
	}

	virtual void EndRollup(IDerivedDataRollup*& Rollup) override
	{
		check(!Rollup); // this needs to be handled by someone else, if rollups are disabled, then it should be NULL
	}

	virtual bool GetSynchronous(const TCHAR* CacheKey, TArray<uint8>& OutData) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_GetSynchronous_Data);
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("GetSynchronous %s"), CacheKey);
		FAsyncTask<FBuildAsyncWorker> PendingTask((FDerivedDataPluginInterface*)NULL, CacheKey, true);
		AddToAsyncCompletionCounter(1);
		PendingTask.StartSynchronousTask();
		OutData = PendingTask.GetTask().Data;
		return PendingTask.GetTask().bSuccess;
	}

	virtual uint32 GetAsynchronous(const TCHAR* CacheKey, IDerivedDataRollup* Rollup = NULL) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_GetAsynchronous_Handle);
		check(!Rollup); // this needs to be handled by someone else, if rollups are disabled, then it should be NULL
		FScopeLock ScopeLock(&SynchronizationObject);
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("GetAsynchronous %s"), CacheKey);
		uint32 Handle = NextHandle();
		FAsyncTask<FBuildAsyncWorker>* AsyncTask = new FAsyncTask<FBuildAsyncWorker>((FDerivedDataPluginInterface*)NULL, CacheKey, false);
		check(!PendingTasks.Contains(Handle));
		PendingTasks.Add(Handle, AsyncTask);
		AddToAsyncCompletionCounter(1);
		AsyncTask->StartBackgroundTask();
		return Handle;
	}

	/** 
	 * Starts the async process of checking the cache and if the item is present, retrieving the cached results (version for internal use by rollups)
	 * @param	CacheKey	Key to identify the data
	 * @param	Rollup		Rollup pointer, if this is part of a rollup
	 * @param	Handle		The handle that can be used for PollAsynchronousCompletion, WaitAsynchronousCompletion and GetAsynchronousResults
	**/
	void GetAsynchronousForRollup(const TCHAR* CacheKey, uint32 Handle)
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_GetAsynchronousForRollup);
		FScopeLock ScopeLock(&SynchronizationObject);
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("GetAsynchronous(handle) %s"), CacheKey);
		FAsyncTask<FBuildAsyncWorker>* AsyncTask = new FAsyncTask<FBuildAsyncWorker>((FDerivedDataPluginInterface*)NULL, CacheKey, false);
		check(!PendingTasks.Contains(Handle));
		PendingTasks.Add(Handle,AsyncTask);
		AddToAsyncCompletionCounter(1);
		AsyncTask->StartBackgroundTask();
	}

	virtual void Put(const TCHAR* CacheKey, TArray<uint8>& Data, bool bPutEvenIfExists = false) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_Put);
		STAT(double ThisTime = 0);
		{
			SCOPE_SECONDS_COUNTER(ThisTime);
			FDerivedDataBackend::Get().GetRoot().PutCachedData(CacheKey, Data, bPutEvenIfExists);
		}
		INC_FLOAT_STAT_BY(STAT_DDC_PutTime,(float)ThisTime);
		INC_DWORD_STAT(STAT_DDC_NumPuts);
	}

	virtual void MarkTransient(const TCHAR* CacheKey) override
	{
		FDerivedDataBackend::Get().GetRoot().RemoveCachedData(CacheKey, /*bTransient=*/ true);
	}

	virtual bool CachedDataProbablyExists(const TCHAR* CacheKey) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_CachedDataProbablyExists);
		bool bResult;
		INC_DWORD_STAT(STAT_DDC_NumExist);
		STAT(double ThisTime = 0);
		{
			SCOPE_SECONDS_COUNTER(ThisTime);
			bResult = FDerivedDataBackend::Get().GetRoot().CachedDataProbablyExists(CacheKey);
		}
		INC_FLOAT_STAT_BY(STAT_DDC_ExistTime, (float)ThisTime);
		return bResult;
	}

	void NotifyBootComplete() override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_NotifyBootComplete);
		FDerivedDataBackend::Get().NotifyBootComplete();
	}

	void AddToAsyncCompletionCounter(int32 Addend) override
	{
		FDerivedDataBackend::Get().AddToAsyncCompletionCounter(Addend);
	}

	void WaitForQuiescence(bool bShutdown) override
	{
		QUICK_SCOPE_CYCLE_COUNTER(STAT_DDC_WaitForQuiescence);
		FDerivedDataBackend::Get().WaitForQuiescence(bShutdown);
	}

	void GetDirectories(TArray<FString>& OutResults) override
	{
		FDerivedDataBackend::Get().GetDirectories(OutResults);
	}

	/** Called at ShutdownModule() time to print out status before we're cleaned up */
	virtual void PrintLeaks()
	{
		// Used by derived classes to spit out leaked pending rollups
	}

	virtual void GatherUsageStats(TMap<FString, FDerivedDataCacheUsageStats>& UsageStatsMap) override
	{
		FDerivedDataBackend::Get().GatherUsageStats(UsageStatsMap);
	}

protected:
	uint32 NextHandle()
	{
		return (uint32)CurrentHandle.Increment();
	}


private:

	/** 
	 * Internal function to build a cache key out of the plugin name, versions and plugin specific info
	 * @param	DataDeriver	plugin to produce the elements of the cache key.
	 * @return				Assembled cache key
	**/
	static FString BuildCacheKey(FDerivedDataPluginInterface* DataDeriver)
	{
		FString Result = FDerivedDataCacheInterface::BuildCacheKey(DataDeriver->GetPluginName(), DataDeriver->GetVersionString(), *DataDeriver->GetPluginSpecificCacheKeySuffix());
		return Result;
	}


	/** Counter used to produce unique handles **/
	FThreadSafeCounter			CurrentHandle;
	/** Object used for synchronization via a scoped lock **/
	FCriticalSection			SynchronizationObject;
	/** Map of handle to pending task **/
	TMap<uint32,FAsyncTask<FBuildAsyncWorker>*>	PendingTasks;
};

//Forward reference
FDerivedDataCache& InternalSingleton();

namespace EPhase
{
	enum Type
	{
		Adding,
		AsyncRollupGet,
		AsyncRollupGetSucceed,
		AsyncRollupGetFailed_GettingItemsAndWaitingForPuts,
		Done,
	};
}

/** 
 * Opaque class for rollup handling
**/
class FDerivedDataRollup : public IDerivedDataRollup
{
	/** Magic numbers to verify integrity and check endianness **/
	enum
	{
		MAGIC=0x9E1B83C1,
		MAGIC_SWAPPED=0xC1831B9E
	};

	/** Helper structure for an element of a rollup **/
	struct FRollupItem
	{
		FRollupItem(const FString& InCacheKey, uint32 InAsyncHandle)
			: CacheKey(InCacheKey)
			, AsyncHandle(InAsyncHandle)
			, FinishedFromThePerspectiveOfTheCaller(false)
		{
		}
		/** Cache key for this item **/
		FString CacheKey;
		/** Async handle for this item, used both to return to original caller, and for calls to the actual DDC **/
		uint32 AsyncHandle;
		/** Payload of this item, used for both from the get of the rollup and a put to the rollup **/
		TArray<uint8> Payload;
		/** If true, then the caller has either asked for the results. This means we don't need to keep them any more. **/
		bool FinishedFromThePerspectiveOfTheCaller;
	};

	/** Items in this rollup **/
	TArray<FRollupItem> Items;
	/** Redundant copy of the keys in this rollup **/
	TSet<FString> CacheKeys;
	/** Redundant copy of the async handles in this rollup **/
	TSet<uint32> AsyncHandles;
	/** Cache key for the rollup itself **/
	FString RollupCacheKey;
	/** Async handle for the rollup **/
	uint32 RollupAsyncHandle;
	/** Tracks the phase this rollup is in. Mostly used for check's **/
	EPhase::Type CurrentPhase;
	/** If true, the rollup was corrupted, so we need to force a put when we get to the put. **/
	bool ForcePutForCorruption;

	/** Called when the rollup is ready. This is indirectly caused by the original caller waiting for an item to be ready. **/
	void GetRollupResults()
	{
		check(Items.Num());
		check(CurrentPhase == EPhase::AsyncRollupGet);
		TArray<uint8> Payload;
		bool bFailed = true;
		if (InternalSingleton().FDerivedDataCache::GetAsynchronousResults(RollupAsyncHandle, Payload))
		{
			ForcePutForCorruption = true;
			if (Payload.Num() > sizeof(uint32) * 2)
			{
				FMemoryReader Ar(Payload);
				uint32 Magic;
				Ar << Magic;
				if (Magic == MAGIC_SWAPPED)
				{
					Ar.SetByteSwapping(!Ar.ForceByteSwapping());
					Magic = MAGIC;
				}
				if (Magic == MAGIC)
				{
					int32 Count;
					Ar << Count;
					if (Count == Items.Num())
					{
						bFailed = false;
						for (int32 Index = 0; Index < Items.Num(); Index++)
						{
							FString Key;
							Ar << Key;
							if (Key != Items[Index].CacheKey)
							{
								bFailed = true;
								break;
							}
							Ar << Items[Index].Payload;
							if (!Items[Index].Payload.Num())
							{
								bFailed = true;
								break;
							}
						}
					}
				}
			}
		}
		if (!bFailed)
		{
			ForcePutForCorruption = false;
			CurrentPhase = EPhase::AsyncRollupGetSucceed;
		}
		else
		{
			CurrentPhase = EPhase::AsyncRollupGetFailed_GettingItemsAndWaitingForPuts;
			for (int32 Index = 0; Index < Items.Num(); Index++)
			{
				Items[Index].Payload.Empty(); // we might have had partial success on a corrupted rollup; we won't accept those
				InternalSingleton().FDerivedDataCache::GetAsynchronousForRollup(*Items[Index].CacheKey, Items[Index].AsyncHandle);
			}
		}
	}

	/** Tests to see if the rollup is complete and ready to be put; if it is, it packages it and puts it. **/
	bool CheckForPut()
	{
		check(Items.Num());
		check(CurrentPhase == EPhase::AsyncRollupGetFailed_GettingItemsAndWaitingForPuts);
		for (int32 Index = 0; Index < Items.Num(); Index++)
		{
			if (!Items[Index].Payload.Num())
			{
				return false; // not done yet because we don't have all of the data
			}
			if (!Items[Index].FinishedFromThePerspectiveOfTheCaller)
			{
				return false; // not done yet because the caller still hasn't retrieved their results
			}
		}
		uint32 Magic = MAGIC;
		int32 Count = Items.Num();
		TArray<uint8> Buffer;
		FMemoryWriter Ar(Buffer);
		Ar << Magic;
		Ar << Count;
		for (int32 Index = 0; Index < Items.Num(); Index++)
		{
			Ar << Items[Index].CacheKey;
			Ar << Items[Index].Payload;
		}
		InternalSingleton().FDerivedDataCache::Put(*RollupCacheKey, Buffer, ForcePutForCorruption);
		CurrentPhase = EPhase::Done;
		return true;
	}

	/** 
	 * Checks to see if there is any reason for this rollup to stay alive. 
	 * @return true when done
	**/
	bool CheckForDone()
	{
		check(Items.Num());
		check(CurrentPhase == EPhase::AsyncRollupGetSucceed);
		for (int32 Index = 0; Index < Items.Num(); Index++)
		{
			if (!Items[Index].FinishedFromThePerspectiveOfTheCaller)
			{
				return false; // not done yet because the caller still hasn't retrieved their results
			}
			if (!Items[Index].Payload.Num())
			{
				check(0); // what is this?
			}
		}
		CurrentPhase = EPhase::Done;
		return true;
	}

	/** 
	 * Finds an item by async handle, not legal to call if this rollup does not contain this handle
	 * @param Handle		Async handle to find the corresponding item of
	 * @return				Item with this async handle
	**/
	FRollupItem& FindItem(uint32 Handle)
	{
		for (int32 Index = 0; Index < Items.Num(); Index++)
		{
			if (Items[Index].AsyncHandle == Handle)
			{
				return Items[Index];
			}
		}
		UE_LOG(LogDerivedDataCache, Fatal, TEXT("Illegal async handle passed to FRollupItem::FindItem()."));
		return Items[0];// shouldn't get here anyway, won't make it worse
	}

	/** 
	 * Finds an item by cache key, not legal to call if this rollup does not contain this cache key
	 * @param InCacheKey	cache key to find the corresponding item of
	 * @return				Item with this cache key
	**/
	FRollupItem& FindItem(const FString& InCacheKey)
	{
		for (int32 Index = 0; Index < Items.Num(); Index++)
		{
			if (Items[Index].CacheKey == InCacheKey)
			{
				return Items[Index];
			}
		}
		UE_LOG(LogDerivedDataCache, Fatal, TEXT("Illegal cache key passed to FRollupItem::FindItem()."));
		return Items[0];// shouldn't get here anyway, won't make it worse
	}

public:
	FDerivedDataRollup()
		: RollupCacheKey(TEXT("ROLLUP_"))
		, RollupAsyncHandle(0)
		, CurrentPhase(EPhase::Adding)
		, ForcePutForCorruption(false)
	{
	}

	/** Return the cache key, used for error spew **/
	FString GetName()
	{
		return RollupCacheKey;
	}

	/** Return true if this rollup can be deleted because it has completed its life cycle. **/
	bool IsDone()
	{
		return CurrentPhase == EPhase::Done;
	}

	/** Return true if this rollup contains an item with the given cache key. **/
	bool Contains(const FString& InCacheKey)
	{
		return CacheKeys.Contains(InCacheKey);
	}

	/** Return true if this rollup contains an item with the given async handle. **/
	bool Contains(uint32 InAsyncHandle)
	{
		return AsyncHandles.Contains(InAsyncHandle);
	}

	/** Add a new item to this rollup with the given cache key and async handle. **/
	void Add(const FString& InCacheKey, uint32 InAsyncHandle)
	{
		check(CurrentPhase == EPhase::Adding);
		RollupCacheKey += InCacheKey;
		CacheKeys.Add(InCacheKey);
		AsyncHandles.Add(InAsyncHandle);
		new (Items) FRollupItem(InCacheKey, InAsyncHandle);
	}

	/** Signifies the end of the adding phase and starts an async get of the rollup. **/
	void Close()
	{
		check(CurrentPhase == EPhase::Adding);
		if (Items.Num())
		{
			RollupAsyncHandle = InternalSingleton().FDerivedDataCache::GetAsynchronous(*RollupCacheKey);
			CurrentPhase = EPhase::AsyncRollupGet;
		}
		else
		{
			CurrentPhase = EPhase::Done;
		}
	}

	/** 
	 * Handle PollAsynchronousCompletion from the calling code. 
	 * @param Handle	Async completion handle for the item
	 * @return			true, if the calling code can request results yet
	 **/
	bool PollAsynchronousCompletion(uint32 Handle)
	{
		check(Contains(Handle));
		if (CurrentPhase == EPhase::AsyncRollupGet)
		{
			// in this phase we see if the rollup is done
			if (!InternalSingleton().FDerivedDataCache::PollAsynchronousCompletion(RollupAsyncHandle))
			{
				return false;
			}
			GetRollupResults();
			// fall through to handle the other cases
		}
		if (CurrentPhase == EPhase::AsyncRollupGetSucceed)
		{
			// Rollup succeeded, so the calling code can get the results
			return true;
		}
		if (CurrentPhase == EPhase::AsyncRollupGetFailed_GettingItemsAndWaitingForPuts)
		{
			// Rollup failed, so call the actual PAC for the individual item
			return InternalSingleton().FDerivedDataCache::PollAsynchronousCompletion(Handle);
		}
		check(0); // bad phase
		return false;
	}

	/** 
	 * Handle WaitAsynchronousCompletion from the calling code. 
	 * @param Handle	Async completion handle for the item
	 **/
	void WaitAsynchronousCompletion(uint32 Handle)
	{
		check(Contains(Handle));
		if (CurrentPhase == EPhase::AsyncRollupGet)
		{
			// in this phase we wait for the rollup to complete, then deal with the results
			InternalSingleton().FDerivedDataCache::WaitAsynchronousCompletion(RollupAsyncHandle);
			GetRollupResults();
			// fall through to handle the other cases
		}
		if (CurrentPhase == EPhase::AsyncRollupGetSucceed)
		{
			// Rollup succeeded, so the calling code can get the results
			return;
		}
		if (CurrentPhase == EPhase::AsyncRollupGetFailed_GettingItemsAndWaitingForPuts)
		{
			// Rollup failed, so call the actual WAC for the individual item
			InternalSingleton().FDerivedDataCache::WaitAsynchronousCompletion(Handle);
			return;
		}
		check(0); // bad phase
	}

	/** 
	 * Handle GetAsynchronousResults from the calling code. If this is the last piece of data, the rollup will be put.
	 * @param Handle	Async completion handle for the item
	 * @param OutData	returned payload
	 * @return			true if the payload contains data and everything is peachy
	 **/
	bool GetAsynchronousResults(uint32 Handle, TArray<uint8>& OutData, bool* bDataWasBuilt)
	{
		check(Contains(Handle));
		FRollupItem& Item = FindItem(Handle);
		Item.FinishedFromThePerspectiveOfTheCaller = true;
		OutData.Empty();
		if (CurrentPhase == EPhase::AsyncRollupGetSucceed)
		{
			if (bDataWasBuilt)
			{
				*bDataWasBuilt = false;
			}
			OutData = Item.Payload;
			CheckForDone();
			return !!OutData.Num();
		}
		if (CurrentPhase == EPhase::AsyncRollupGetFailed_GettingItemsAndWaitingForPuts)
		{
			if (InternalSingleton().FDerivedDataCache::GetAsynchronousResults(Handle, OutData, bDataWasBuilt))
			{
				Item.Payload = OutData;
				CheckForPut();
			}
			return !!OutData.Num();
		}
		check(0); // bad phase
		return false;
	}
	/** 
	 * Handle Put from the calling code. If this is the last piece of data, the rollup will be put.
	 * @param CacheKey	Cache key for the item
	 * @param Data		returned payload
	 **/
	void Put(const TCHAR* CacheKey, TArray<uint8>& Data)
	{
		if (CurrentPhase != EPhase::AsyncRollupGetFailed_GettingItemsAndWaitingForPuts)
		{
			return;
		}
		check(Contains(CacheKey));
		FRollupItem& Item = FindItem(CacheKey);
		check(Data.Num());
		Item.Payload = Data;
		CheckForPut();
	}
};



/** 
 * Implementation of the derived data cache, this layer implements rollups
**/
class FDerivedDataCacheWithRollups : public FDerivedDataCache
{
	typedef FDerivedDataCache Super;
public:

	~FDerivedDataCacheWithRollups()
	{
	}

	virtual void PrintLeaks() override
	{
		FScopeLock ScopeLock(&SynchronizationObject);
		UE_LOG(LogDerivedDataCache, Log, TEXT("Shutdown"));
		for (TSet<FDerivedDataRollup*>::TIterator Iter(PendingRollups); Iter; ++Iter)
		{
			FString Name((*Iter)->GetName());
			if (Name.Len() > 1024)
			{
				Name = Name.Left(1024);
				Name += TEXT("...");
			}
			UE_LOG(LogDerivedDataCache, Warning, TEXT("Leaked Rollup! %s"), *Name);
		}
		//check(!PendingRollups.Num()); // leaked rollups
	}

	virtual bool PollAsynchronousCompletion(uint32 Handle) override
	{
		FScopeLock ScopeLock(&SynchronizationObject);
		for (TSet<FDerivedDataRollup*>::TIterator Iter(PendingRollups); Iter; ++Iter)
		{
			if ((*Iter)->Contains(Handle))
			{
				return (*Iter)->PollAsynchronousCompletion(Handle);
			}
		}
		return Super::PollAsynchronousCompletion(Handle);
	}

	virtual void WaitAsynchronousCompletion(uint32 Handle) override
	{
		STAT(double ThisTime = 0);
		{
			SCOPE_SECONDS_COUNTER(ThisTime);
			FScopeLock ScopeLock(&SynchronizationObject);
			for (TSet<FDerivedDataRollup*>::TIterator Iter(PendingRollups); Iter; ++Iter)
			{
				if ((*Iter)->Contains(Handle))
				{
					(*Iter)->WaitAsynchronousCompletion(Handle);
					return;
				}
			}
		}
		INC_FLOAT_STAT_BY(STAT_DDC_ASyncWaitTime,(float)ThisTime);
		Super::WaitAsynchronousCompletion(Handle);
	}

	virtual bool GetAsynchronousResults(uint32 Handle, TArray<uint8>& OutData, bool* bDataWasBuilt = nullptr) override
	{
		FScopeLock ScopeLock(&SynchronizationObject);
		for (TSet<FDerivedDataRollup*>::TIterator Iter(PendingRollups); Iter; ++Iter)
		{
			if ((*Iter)->Contains(Handle))
			{
				bool Result = (*Iter)->GetAsynchronousResults(Handle, OutData, bDataWasBuilt);
				if ((*Iter)->IsDone())
				{
					delete *Iter;
					Iter.RemoveCurrent();
				}
				return Result;
			}
		}
		return Super::GetAsynchronousResults(Handle, OutData, bDataWasBuilt);
	}

	virtual IDerivedDataRollup* StartRollup() override
	{
		FScopeLock ScopeLock(&SynchronizationObject);
		FDerivedDataRollup* Result = new FDerivedDataRollup();
		PendingRollups.Add(Result);
		return Result;
	}

	virtual void EndRollup(IDerivedDataRollup*& InRollup) override
	{
		FDerivedDataRollup* Rollup = static_cast<FDerivedDataRollup*>(InRollup);
		if (Rollup)
		{
			FScopeLock ScopeLock(&SynchronizationObject);
			Rollup->Close();
			if (Rollup->IsDone())
			{
				PendingRollups.Remove(Rollup);
				delete Rollup;
			}
			InRollup = NULL; // set the pointer to NULL so it cannot be reused
		}
	}

	virtual uint32 GetAsynchronous(const TCHAR* CacheKey, IDerivedDataRollup* Rollup = NULL) override
	{
		if (Rollup)
		{
			FScopeLock ScopeLock(&SynchronizationObject);
			UE_LOG(LogDerivedDataCache, Verbose, TEXT("GetAsynchronous (Rollup) %s"), CacheKey);
			const uint32 RollupHandle = NextHandle();
			((FDerivedDataRollup*)Rollup)->Add(CacheKey, RollupHandle);
			return RollupHandle;
		}
		return Super::GetAsynchronous(CacheKey, nullptr);
	}

	virtual void Put(const TCHAR* CacheKey, TArray<uint8>& Data, bool bPutEvenIfExists = false) override
	{
		FScopeLock ScopeLock(&SynchronizationObject);
		for (TSet<FDerivedDataRollup*>::TIterator Iter(PendingRollups); Iter; ++Iter)
		{
			if ((*Iter)->Contains(CacheKey))
			{
				(*Iter)->Put(CacheKey, Data);
				if ((*Iter)->IsDone())
				{
					delete *Iter;
					Iter.RemoveCurrent();
				}
			}
		}
		return Super::Put(CacheKey, Data, bPutEvenIfExists);
	}

private:

	/** Object used for synchronization via a scoped lock **/
	FCriticalSection			SynchronizationObject;
	/** Set of rollups **/
	TSet<FDerivedDataRollup*>	PendingRollups;
};

/**
 * Singleton used both internally, and through the module.
 * We look at the commandline to check if we should disable rollups or not
 */
FDerivedDataCache& InternalSingleton()
{
	static FDerivedDataCache* Singleton = NULL;
	if (!Singleton)
	{
		if (FParse::Param(FCommandLine::Get(), TEXT("DDCNoRollups")))
		{
			UE_LOG(LogDerivedDataCache, Warning, TEXT("Rollups are disabled."));
			static FDerivedDataCache SingletonInstance;
			Singleton = &SingletonInstance;
		}
		else
		{
			static FDerivedDataCacheWithRollups SingletonInstance;
			Singleton = &SingletonInstance;
		}
	}
	return *Singleton;
}

/**
 * Module for the DDC
 */
class FDerivedDataCacheModule : public IDerivedDataCacheModule
{
	/** Cached reference to DDC singleton, helpful to control singleton's lifetime. */
	FDerivedDataCache* DDC;

public:
	virtual FDerivedDataCacheInterface& GetDDC() override
	{
		return InternalSingleton();
	}

	virtual void StartupModule() override
	{

		// make sure DDC gets created early, previously it might have happened in ShutdownModule() (for PrintLeaks()) when it was already too late
		DDC = static_cast< FDerivedDataCache* >( &GetDDC() );
	}

	virtual void ShutdownModule() override
	{
		FDDCCleanup::Shutdown();

		if (DDC)
		{
			DDC->PrintLeaks();
		}
	}

	FDerivedDataCacheModule()
		:	DDC(nullptr)
	{
	}
};

IMPLEMENT_MODULE( FDerivedDataCacheModule, DerivedDataCache);