how to access a worker thread from UI thread?

Question

I have a working thread running all along the runtime, who generates events.

I can handle those events inside the UI thread by using disp = Windows::UI::Core::CoreWindow::GetForCurrentThread()->Dispatcher.

more precisely, I do the modifications to the UI by using disp->RunAsync(...) anywhere inside the working thread.

but I don't know how to do the inverted operation. I want to have some Async function inside the UI thread to perform operation (on some std::unique_ptr) in the working thread when I click on some button.

Answer 1

If I understand correctly you want to be able to run an async operation when a button is clicked, but on a specific thread to which you refer as your worker thread.

First - Since you want to use a resource in 2 threads you should not use unique_ptr and use shared_ptr since you share this resource between the two threads.

Second - if you don't necessarily have to run the action on a specific thread then you can simply use Windows::System::Threading::ThreadPool::RunAsync and capture the shared_ptr by value.

e.g:

namespace WST = Windows::System::Threading;

WST::ThreadPool::RunAsync(
    ref new WST::WorkItemHandler(
            [mySharedPtr](Windows::Foundation::IAsyncAction^ operation)
            {
                mySharedPtr->Foo();
            }));

In case you have to run the operation on a specific thread then I assume you want to be able to append operations to an already running thread, otherwise you are creating a thread and you can use the above example. So in order to append operations to an already running thread, that thread must have the functionality of getting a new operations and then running those operations in a synchronous order. This functionality is basically what the Dispatcher provides. This is what an Event Loop is, also called: message dispatcher, message loop, message pump, or run loop. Also you can find information by reading on the Recator\Proactor design pattern.

This CodeProject page shows one way of implementing the pattern, and you can use Winrt component to make it better \ more conveniant \ more familiar