Can we create and destroy winrt::hstring 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::hstring across threads. Specifically, if I create a winrt::hstring on one thread (Thread 1) and pass its ABI pointer to another thread (Thread 2), can I safely destroy the string on Thread 2?

Here’s the setup:

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

void threadFunc1()
{
    winrt::hstring myString = L"Hello, WinRT!";

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

void threadFunc2()
{
	// Reconstruct the hstring from ABI pointer
    winrt::hstring myString2(ptr, winrt::take_ownership_from_abi);  
}

This code works as expected: I’m able to create the winrt::hstring 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 in advance for any insights!

Answer 1

Hello @Shyam Butani ,

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?

winrt::hstring doesn't really have anything to do with COM. It does not require a COM apartment at all. Internally, it is implemented in terms of HeapAlloc / HeapFree and nothing more.

can I safely destroy the string on Thread 2?

And so yes you can create it on one thread and destroy it on another. More generally, it an be transferred across thread boundaries and it is safe to share references between threads. 

Thank you.

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