Adding State to the Update Notification Pattern, Part 7 -- Raymond Chen

RaymondChen_5in-150x150.jpgLast time, we refined our change counter-based stateful but coalescing update notification. This version still relies on a UI thread to do two things: (1) make the final final change counter check and the subsequent callback atomic, and (2) to serialize the callbacks.

Adding State to the Update Notification Pattern, Part 7

by Raymond Chen

From the article:

If we don’t have a UI thread, then we open a race condition.

class EditControl
    ⟦ ... existing class members ... ⟧

    std::atomic<unsigned> m_latestId;

EditControl::TextChanged(std::string text)
    auto lifetime = get_strong();

    auto id = m_latestId.fetch_add(1, std::memory_order_relaxed);

    co_await winrt::resume_background();

    if (!IsLatestId(id))) co_return;

    std::vector<std::string> matches;
    for (auto&& candidate : FindCandidates(text)) {
        if (candidate.Verify()) {
        if (!IsLatestId(id))) co_return;

    // co_await winrt::resume_foreground(Dispatcher());

    if (!IsLatestId(id))) co_return;


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