Proper way to pass same pointer to 2 threads(each thread runs another operation)

Question

What is the proper way to pass a pointer to 2 threads that each one of the threads runs another operation?

#include <chrono>
#include <iostream>
#include <vector>
#include <thread>
#include <random>


struct Unit {

    Unit(uint64_t id_) :
        id(id_),
        v(1000000000)
    {}

    uint64_t id;
    std::vector<int> v;
};

void operation1(Unit* unit) {
    std::cout << "Hello operation1";
}

void operation2(Unit* unit) {
    std::cout << "Hello operation2";
}

void operationMain() {
    Unit* unit = new Unit(1);
    std::thread at1(&operation1, unit);
    std::thread at2(&operation2, unit);
    at1.detach();
    at2.detach();
}

int main123(int argc, char** argv)
{
    std::thread t(&operationMain);
    t.join();

    return 0;
}

Here is my code, and I think I have a memory leak because 'unit' is passing to several operations in different threads.

Any suggestions?

The threads are irrelevant and a red herring. If you do new without a corresponding delete you have a memory leak. — Some programmer dude
– Some programmer dude, Commented Aug 25, 2022 at 10:18
Any reason you aren't using smart pointers, particularly std::shared_ptr? The rest of the code seems to use C++11 features — Homer512
– Homer512, Commented Aug 25, 2022 at 10:24
Please read up on the proper use of smart pointers. Using new and delete is rarely used in modern C++ — Homer512
– Homer512, Commented Aug 25, 2022 at 12:07
Can you provide an example of smart pointers based on my code please? — David
– David, Commented Aug 25, 2022 at 12:14

Persixty · Accepted Answer · 2022-08-25 19:17:05Z

My suggestion is to not use detach() but use join() or not share the object or create one of in (say) the at1 thread, detach() it and create at2 the as a thread within that second thread and join in the at1 thread or allocated a shared_ptr<> but shared ownership is way down the list as 'avoid where possible'.

detach() means a thread executes independently and you cannot call join() on a detached thread so you have no suitable point at which to cause the delete of the dynamically allocated Unit to take place in the calling thread.

It's not clear from the question why you've allocated shared resources and then called detach().

On my machine I get no output (even with a realistic size for the vector) because the main() thread ends before the detach threads do anything meaningful.

This should work fine:

void operationMain() {
       std::unique_ptr<Unit> unit (std::make_unique<Unit>(1));
       std::thread at1(operation1, unit.get());
       std::thread at2(operation2, unit.get());
       at1.join();        
       at2.join();
       //at1 and at2 have terminated and the unique_ptr destructor will delete the object (RAII).
}

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