向线程池提交工作项

2025-06-10

[ 已针对 Windows 10 上的 UWP 应用进行了更新。有关 Windows 8.x 文章，请参阅存档 ]

重要的应用程序接口（API）

通过将工作项提交到线程池中，来学习如何在单独的线程中执行工作。使用这个可以保持响应式 UI，同时完成需要较多时间的工作，并行完成多个任务。

创建和提交工作项

通过调用 runAsync 创建工作项。提供一个委托对象来执行工作（可以使用 lambda 表达式或委托函数）。请注意，RunAsync 返回 IAsyncAction 对象;存储此对象以供下一步使用。

RunAsync 的三个版本可用，以便可以选择指定工作项的优先级，并控制它是否与其他工作项同时运行。

注释

使用 CoreDispatcher.RunAsync 访问 UI 线程并显示工作项的进度。

以下示例创建一个工作项并提供 lambda 来执行该工作：

// The nth prime number to find.
const uint n = 9999;

// Receives the result.
ulong nthPrime = 0;

// Simulates work by searching for the nth prime number. Uses a
// naive algorithm and counts 2 as the first prime number.
IAsyncAction asyncAction = Windows.System.Threading.ThreadPool.RunAsync(
    (workItem) =>
{
    uint  progress = 0; // For progress reporting.
    uint  primes = 0;   // Number of primes found so far.
    ulong i = 2;        // Number iterator.

    if ((n >= 0) && (n <= 2))
    {
        nthPrime = n;
        return;
    }

    while (primes < (n - 1))
    {
        if (workItem.Status == AsyncStatus.Canceled)
        {
            break;
        }

        // Go to the next number.
        i++;

        // Check for prime.
        bool prime = true;
        for (uint j = 2; j < i; ++j)
        {
            if ((i % j) == 0)
            {
                prime = false;
                break;
            }
        };

        if (prime)
        {
            // Found another prime number.
            primes++;

            // Report progress at every 10 percent.
            uint temp = progress;
            progress = (uint)(10.0*primes/n);

            if (progress != temp)
            {
                String updateString;
                updateString = "Progress to " + n + "th prime: "
                    + (10 * progress) + "%\n";

                // Update the UI thread with the CoreDispatcher.
                CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(
                    CoreDispatcherPriority.High,
                    new DispatchedHandler(() =>
                {
                    UpdateUI(updateString);
                }));
            }
        }
    }

    // Return the nth prime number.
    nthPrime = i;
});

// A reference to the work item is cached so that we can trigger a
// cancellation when the user presses the Cancel button.
m_workItem = asyncAction;

// The nth prime number to find.
const unsigned int n{ 9999 };

// A shared pointer to the result.
// We use a shared pointer to keep the result alive until the
// work is done.
std::shared_ptr<unsigned long> nthPrime = std::make_shared<unsigned long>(0);

// Simulates work by searching for the nth prime number. Uses a
// naive algorithm and counts 2 as the first prime number.

// A reference to the work item is cached so that we can trigger a
// cancellation when the user presses the Cancel button.
m_workItem = Windows::System::Threading::ThreadPool::RunAsync(
    [=, strongThis = get_strong()](Windows::Foundation::IAsyncAction const& workItem)
{
    unsigned int progress = 0; // For progress reporting.
    unsigned int primes = 0;   // Number of primes found so far.
    unsigned long int i = 2;   // Number iterator.

    if ((n >= 0) && (n <= 2))
    {
        *nthPrime = n;
        return;
    }

    while (primes < (n - 1))
    {
        if (workItem.Status() == Windows::Foundation::AsyncStatus::Canceled)
        {
            break;
        }

        // Go to the next number.
        i++;

        // Check for prime.
        bool prime = true;
        for (unsigned int j = 2; j < i; ++j)
        {
            if ((i % j) == 0)
            {
                prime = false;
                break;
            }
        };

        if (prime)
        {
            // Found another prime number.
            primes++;

            // Report progress at every 10 percent.
            unsigned int temp = progress;
            progress = static_cast<unsigned int>(10.f*primes / n);

            if (progress != temp)
            {
                std::wstringstream updateStream;
                updateStream << L"Progress to " << n << L"th prime: " << (10 * progress) << std::endl;
                std::wstring updateString = updateStream.str();

                // Update the UI thread with the CoreDispatcher.
                Windows::ApplicationModel::Core::CoreApplication::MainView().CoreWindow().Dispatcher().RunAsync(
                    Windows::UI::Core::CoreDispatcherPriority::High,
                    Windows::UI::Core::DispatchedHandler([=]()
                {
                    strongThis->UpdateUI(updateString);
                }));
            }
        }
    }
    // Return the nth prime number.
    *nthPrime = i;
});

// The nth prime number to find.
const unsigned int n = 9999;

// A shared pointer to the result.
// We use a shared pointer to keep the result alive until the
// work is done.
std::shared_ptr<unsigned long> nthPrime = std::make_shared<unsigned long>(0);

// Simulates work by searching for the nth prime number. Uses a
// naive algorithm and counts 2 as the first prime number.
auto workItem = ref new Windows::System::Threading::WorkItemHandler(
    [this, n, nthPrime](IAsyncAction^ workItem)
{
    unsigned int progress = 0; // For progress reporting.
    unsigned int primes = 0;   // Number of primes found so far.
    unsigned long int i = 2;   // Number iterator.

    if ((n >= 0) && (n <= 2))
    {
        *nthPrime = n;
        return;
    }

    while (primes < (n - 1))
    {
        if (workItem->Status == AsyncStatus::Canceled)
       {
           break;
       }

       // Go to the next number.
       i++;

       // Check for prime.
       bool prime = true;
       for (unsigned int j = 2; j < i; ++j)
       {
           if ((i % j) == 0)
           {
               prime = false;
               break;
           }
       };

       if (prime)
       {
           // Found another prime number.
           primes++;

           // Report progress at every 10 percent.
           unsigned int temp = progress;
           progress = static_cast<unsigned int>(10.f*primes / n);

           if (progress != temp)
           {
               String^ updateString;
               updateString = "Progress to " + n + "th prime: "
                   + (10 * progress).ToString() + "%\n";

               // Update the UI thread with the CoreDispatcher.
               CoreApplication::MainView->CoreWindow->Dispatcher->RunAsync(
                   CoreDispatcherPriority::High,
                   ref new DispatchedHandler([this, updateString]()
               {
                   UpdateUI(updateString);
               }));
           }
       }
   }
   // Return the nth prime number.
   *nthPrime = i;
});

auto asyncAction = ThreadPool::RunAsync(workItem);

// A reference to the work item is cached so that we can trigger a
// cancellation when the user presses the Cancel button.
m_workItem = asyncAction;

调用 RunAsync后，工作项由线程池排队，并在线程可用时运行。线程池工作项以异步方式运行，并且可以按任意顺序运行，因此请确保工作项独立运行。

请注意，工作项会检查 IAsyncInfo.Status 属性，并在该工作项被取消时退出。

处理工作项的完成

通过设置工作项的 IAsyncAction.Completed 属性来提供完成处理程序。提供一个委托（可以使用一个lambda表达式或委托函数）以处理工作项的完成。例如，使用 CoreDispatcher.RunAsync 访问 UI 线程并显示结果。

以下示例通过步骤 1 中提交的工作项结果来更新 UI：

asyncAction->Completed = ref new AsyncActionCompletedHandler(
    [this, n, nthPrime](IAsyncAction^ asyncInfo, AsyncStatus asyncStatus)
{
    if (asyncStatus == AsyncStatus::Canceled)
    {
        return;
    }

    String^ updateString;
    updateString = "\n" + "The " + n + "th prime number is "
        + (*nthPrime).ToString() + ".\n";

    // Update the UI thread with the CoreDispatcher.
    CoreApplication::MainView->CoreWindow->Dispatcher->RunAsync(
        CoreDispatcherPriority::High,
        ref new DispatchedHandler([this, updateString]()
    {
        UpdateUI(updateString);
    }));
});

m_workItem.Completed(
    [=, strongThis = get_strong()](Windows::Foundation::IAsyncAction const& asyncInfo, Windows::Foundation::AsyncStatus const& asyncStatus)
{
    if (asyncStatus == Windows::Foundation::AsyncStatus::Canceled)
    {
        return;
    }

    std::wstringstream updateStream;
    updateStream << std::endl << L"The " << n << L"th prime number is " << *nthPrime << std::endl;
    std::wstring updateString = updateStream.str();

    // Update the UI thread with the CoreDispatcher.
    Windows::ApplicationModel::Core::CoreApplication::MainView().CoreWindow().Dispatcher().RunAsync(
        Windows::UI::Core::CoreDispatcherPriority::High,
        Windows::UI::Core::DispatchedHandler([=]()
    {
        strongThis->UpdateUI(updateString);
    }));
});

asyncAction.Completed = new AsyncActionCompletedHandler(
    (IAsyncAction asyncInfo, AsyncStatus asyncStatus) =>
{
    if (asyncStatus == AsyncStatus.Canceled)
    {
        return;
    }

    String updateString;
    updateString = "\n" + "The " + n + "th prime number is "
        + nthPrime + ".\n";

    // Update the UI thread with the CoreDispatcher.
    CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(
        CoreDispatcherPriority.High,
        new DispatchedHandler(()=>
    {
        UpdateUI(updateString);
    }));
});

请注意，完成处理程序在调度 UI 更新之前检查工作项是否已取消。

摘要和后续步骤

若要了解详细信息，可以下载本快速入门中的代码，创建针对 Windows 8.1 编写的 ThreadPool 工作项示例，并在 win_unap Windows 10 应用中重新使用源代码。

通过

向线程池提交工作项

创建和提交工作项

处理工作项的完成

摘要和后续步骤

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