Can we create and destroy winrt::IObservableVector on different threads?

Question

Hello,

I’m working on a multi-threaded WinRT/C++ application and need some clarification on how thread safety works when using winrt::IObservableVector across threads. Specifically, if I create a IObservableVector on one thread (Thread 1) and pass its ABI pointer to another thread (Thread 2), can I safely destroy it on Thread 2?

Here’s the setup:

int main()
{
    // Initialize COM on Main thread
    winrt::init_apartment(apartment_type::single_threaded);
}

void threadFunc1()
{
    IObservableVector vec = winrt::single_threaded_observable_vector<int>();

    ptr = detach_abi(vec); // Store ABI pointer in ptr
}

void threadFunc2()
{
    // Destroy (decrement ref count) on different thread
    ((IUnknown*)ptr)->Release();
}

This code works as expected: I’m able to create the IObservableVector on Thread 1 and destroy it on Thread 2. My question is, how does this work under the hood? Is COM initialized for all threads involved, or is there some other mechanism in place that makes this safe?

Thanks.

Answer 1

Hello @Shyam Butani ,

winrt::single_threaded_observable_vector is safe to use from a single thread but is not safe to use from multiple threads.you are using it on multiple threads, which is a violation of the rules, and the results are undefined.

If you want an IObservableVector that is multithread safe, it is recommended to use multi_threaded_observable_vector.

Thank you.

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