#include <iostream>
#include <vector>
#include <queue>
#include <thread>
#include <atomic>
#include <chrono>
#include <mutex>

class MyClass {
public:
    MyClass() { 
        message = new char[2048];
    }
    ~MyClass() { delete message; }

private:
    char* message;
};

// Function to create objects
std::vector<MyClass*> createObjects(size_t numObjects) {
    std::vector<MyClass*> objects;
    objects.reserve(numObjects);
    for (size_t i = 0; i < numObjects; ++i) {
        objects.push_back(new MyClass());
    }
    return objects;
}

// Function to delete objects in a thread
void deleteObjects(std::queue<MyClass*>& objectsQueue) {
    auto start = std::chrono::high_resolution_clock::now();
    size_t deletetime = 0;
    while (!objectsQueue.empty()) {
        delete objectsQueue.front();
        objectsQueue.pop();
    }

    auto end = std::chrono::high_resolution_clock::now();
    deletetime += std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count();
    std::cout << "thread deletion time: " << deletetime << " ms" << std::endl;}

int main() {
    const size_t numObjects = 20000000;
    const size_t numThreads = 4;

    // Step 1: Create all objects
    std::vector<MyClass*> objects = createObjects(numObjects);

    // Step 2: Divide objects among threads
    std::vector<std::queue<MyClass*>> threadQueues(numThreads);
    for (size_t i = 0; i < numObjects; ++i) {
        threadQueues[i % numThreads].push(objects[i]);
    }
    
    // Step 3: Delete objects in threads
    std::vector<std::thread> threads;

    for (size_t i = 0; i < numThreads; ++i) {
        threads.emplace_back(deleteObjects, std::ref(threadQueues[i]));
    }

    // Join all threads
    for (auto& thread : threads) {
        thread.join();
    }

    return 0;
}

I run above code on visual studio 2017 on windows 10

result is
thread deletion time: 1086 ms
thread deletion time: 1252 ms
thread deletion time: 1259 ms
thread deletion time: 62670 ms

3 threads are fast, but last one takes too long.

Does any one know why this is happened?

I expect all thread done that tasks almost same time.