How to use thread safe container in UE5

Development Programming & Scripting C++
, , , , , , , , , , , , , ,
1

Hi, I’m new to UE5 and trying to make a simplest multithreading function.

void AThreadTester::RunStep3()
{
    int32 NumThreads = 20; // Number of threads to create

    // Array to hold the promises for each thread
    TArray<TPromise<TArray<int>>*> Promises;
    Promises.Reserve(NumThreads);

    TDiscardableKeyValueCache<int32, int> ThreadResultsCache;

    // Create promises and run threads
    for (int32 i = 0; i < NumThreads; ++i)
    {
        // Create a new promise for this thread
        TPromise<TArray<int>>* Promise = new TPromise<TArray<int>>();
        Promises.Add(Promise);

        // Set up the callback for the promise
        Promise->GetFuture().Next([i, &ThreadResultsCache](TArray<int> Result)
            {
                UE_LOG(LogTemp, Warning, TEXT("Thread %d result: %d"), i, Result.Num());
                ThreadResultsCache.Add(i, Result.Num());
            });
        // Create a new instance of MyRunnable2 and add it to the Runnables array
        MyRunnable2* Runnable = new MyRunnable2(Promise);
        UE_LOG(LogTemp, Warning, TEXT("Thread %d Added"), i);
    }
    UE_LOG(LogTemp, Warning, TEXT("All started"));
}

This function got some error after adding the line for writing to TDiscardableKeyValueCache, though it is a thread safe struct as I was told. The error message was “Exception thrown at 0x00007FFF3E69BD90 (UnrealEditor-Tester.dll) in UnrealEditor.exe: 0xC0000005: Access violation reading location 0x0000000000000008.” on this line in “Future.h”
auto TFutureBase<InternalResultType>::Next(Func Continuation) //-> TFuture<decltype(Continuation(Get()))> { return this->Then([Continuation = MoveTemp(Continuation)](TFuture<InternalResultType> Self) mutable { return Continuation(Self.Get()); <--- Exception Thrown }); }