如何：使用 WRL 完成异步操作

2015-06-09

文档演示如何使用 Windows 运行时 C++ 模板库 (WRL) 启动异步操作并在操作完成时执行工作。

此文档显示两个示例。第一个示例开始异步的计时器并等待计时器过期。在此示例中，在创建对象时，只需指定异步操作。第二个示例运行在后台工作的线程。此示例演示如何使用 Windows 运行时方法返回 IAsyncInfo 接口。 Callback 函数是两个示例的一个重要部分，因为它使他们指定事件处理程序处理异步操作结果。

有关创建一个组件实例并检索属性值的一种更简单的示例，请参见如何：使用 WRL 激活和使用 Windows 运行时组件。

提示

这些示例使用 lambda 表达式定义回调。也可以使用中与函数对象 (functor)，函数指针或 std::function 对象。有关 C++ lambda 表达式的更多信息，请参见 C++ 中的 Lambda 表达式。

示例：使用计时器的使用

以下步骤开始异步的计时器并等待计时器过期。下面是完整的示例。

警告

尽管可以在 Windows 应用商店应用通常使用 WRL，此示例使用图的控制台应用。函数 (如 wprintf_s ) 从 Windows 应用商店应用不可用。有关在 Windows 应用商店应用中使用和函数的类型的更多信息，请参见 CRT 函数不支持 /ZW 和 Win32 和 COM 中存储应用的。

包括 (#include) 任何必需的 Windows 运行时、WRL 或标准 C++ 库标头。

#include <Windows.Foundation.h>
#include <Windows.System.Threading.h>
#include <wrl/event.h>
#include <stdio.h>
#include <Objbase.h>

using namespace ABI::Windows::Foundation;
using namespace ABI::Windows::System::Threading;
using namespace Microsoft::WRL;
using namespace Microsoft::WRL::Wrappers;

Windows.System.Threading.h 声明异步计时器需要的类型。

我们建议您在 .cpp 文件中使用 using namespace 指令使代码更具可读性。

初始化 Windows 运行时。

// Initialize the Windows Runtime.
RoInitializeWrapper initialize(RO_INIT_MULTITHREADED);
if (FAILED(initialize))
{
    return PrintError(__LINE__, initialize);
}

创建接口的一个活动 ABI::Windows::System::Threading::IThreadPoolTimer 工厂。

// Get the activation factory for the IThreadPoolTimer interface.
ComPtr<IThreadPoolTimerStatics> timerFactory;
HRESULT hr = GetActivationFactory(HStringReference(RuntimeClass_Windows_System_Threading_ThreadPoolTimer).Get(), &timerFactory);
if (FAILED(hr))
{
    return PrintError(__LINE__, hr);
}

Windows 运行时使用完全限定的名称标识一类型。 RuntimeClass_Windows_System_Threading_ThreadPoolTimer 参数是包含 Windows 运行时提供并需的运行时类名称的字符串。

创建事件对象，同步主应用程序的 Timer 回调。

// Create an event that is set after the timer callback completes. We later use this event to wait for the timer to complete.  
// This event is for demonstration only in a console app. In most apps, you typically don't wait for async operations to complete.
Event timerCompleted(CreateEventEx(nullptr, nullptr, CREATE_EVENT_MANUAL_RESET, WRITE_OWNER | EVENT_ALL_ACCESS));
hr = timerCompleted.IsValid() ? S_OK : HRESULT_FROM_WIN32(GetLastError());
if (FAILED(hr))
{
    return PrintError(__LINE__, hr);
}

备注

在控制台应用一部分，此事件只用于演示。此示例使用事件以确保可操作完成，在应用之前退出。在大多数应用，通常不可在等待操作完成。

创建在两秒后过期的 IThreadPoolTimer 对象。使用 Callback 函数创建事件处理程序 ( ABI::Windows::System::Threading::ITimerElapsedHandler 对象)。

// Create a timer that prints a message after 2 seconds.

TimeSpan delay;
delay.Duration = 20000000; // 2 seconds.

auto callback = Callback<ITimerElapsedHandler>([&timerCompleted](IThreadPoolTimer* timer) -> HRESULT
{
    wprintf_s(L"Timer fired.\n");

    TimeSpan delay;
    HRESULT hr = timer->get_Delay(&delay);
    if (SUCCEEDED(hr))
    {
        wprintf_s(L"Timer duration: %2.2f seconds.\n", delay.Duration / 10000000.0);
    }

    // Set the completion event and return.
    SetEvent(timerCompleted.Get());
    return hr;
});
hr = callback ? S_OK : E_OUTOFMEMORY;
if (FAILED(hr))
{
    return PrintError(__LINE__, hr);
}

ComPtr<IThreadPoolTimer> timer;
hr = timerFactory->CreateTimer(callback.Get(), delay, &timer);
if (FAILED(hr))
{
    return PrintError(__LINE__, hr);
}

将消息打印到控制台并等待计时器回调完成。所有 ComPtr 和 RAII 对象都离开范围并自动释放。

// Print a message and wait for the timer callback to complete.
wprintf_s(L"Timer started.\nWaiting for timer...\n");

// Wait for the timer to complete.
WaitForSingleObjectEx(timerCompleted.Get(), INFINITE, FALSE);
// All smart pointers and RAII objects go out of scope here.

这是完整示例:

// wrl-consume-async.cpp 
// compile with: runtimeobject.lib
#include <Windows.Foundation.h>
#include <Windows.System.Threading.h>
#include <wrl/event.h>
#include <stdio.h>
#include <Objbase.h>

using namespace ABI::Windows::Foundation;
using namespace ABI::Windows::System::Threading;
using namespace Microsoft::WRL;
using namespace Microsoft::WRL::Wrappers;

// Prints an error string for the provided source code line and HRESULT 
// value and returns the HRESULT value as an int. 
int PrintError(unsigned int line, HRESULT hr)
{
    wprintf_s(L"ERROR: Line:%d HRESULT: 0x%X\n", line, hr);
    return hr;
}

int wmain()
{
    // Initialize the Windows Runtime.
    RoInitializeWrapper initialize(RO_INIT_MULTITHREADED);
    if (FAILED(initialize))
    {
        return PrintError(__LINE__, initialize);
    }

    // Get the activation factory for the IThreadPoolTimer interface.
    ComPtr<IThreadPoolTimerStatics> timerFactory;
    HRESULT hr = GetActivationFactory(HStringReference(RuntimeClass_Windows_System_Threading_ThreadPoolTimer).Get(), &timerFactory);
    if (FAILED(hr))
    {
        return PrintError(__LINE__, hr);
    }

    // Create an event that is set after the timer callback completes. We later use this event to wait for the timer to complete.  
    // This event is for demonstration only in a console app. In most apps, you typically don't wait for async operations to complete.
    Event timerCompleted(CreateEventEx(nullptr, nullptr, CREATE_EVENT_MANUAL_RESET, WRITE_OWNER | EVENT_ALL_ACCESS));
    hr = timerCompleted.IsValid() ? S_OK : HRESULT_FROM_WIN32(GetLastError());
    if (FAILED(hr))
    {
        return PrintError(__LINE__, hr);
    }

    // Create a timer that prints a message after 2 seconds.

    TimeSpan delay;
    delay.Duration = 20000000; // 2 seconds.

    auto callback = Callback<ITimerElapsedHandler>([&timerCompleted](IThreadPoolTimer* timer) -> HRESULT
    {
        wprintf_s(L"Timer fired.\n");

        TimeSpan delay;
        HRESULT hr = timer->get_Delay(&delay);
        if (SUCCEEDED(hr))
        {
            wprintf_s(L"Timer duration: %2.2f seconds.\n", delay.Duration / 10000000.0);
        }

        // Set the completion event and return.
        SetEvent(timerCompleted.Get());
        return hr;
    });
    hr = callback ? S_OK : E_OUTOFMEMORY;
    if (FAILED(hr))
    {
        return PrintError(__LINE__, hr);
    }

    ComPtr<IThreadPoolTimer> timer;
    hr = timerFactory->CreateTimer(callback.Get(), delay, &timer);
    if (FAILED(hr))
    {
        return PrintError(__LINE__, hr);
    }

    // Print a message and wait for the timer callback to complete.
    wprintf_s(L"Timer started.\nWaiting for timer...\n");

    // Wait for the timer to complete.
    WaitForSingleObjectEx(timerCompleted.Get(), INFINITE, FALSE);
    // All smart pointers and RAII objects go out of scope here.
}
/*
Output:
Timer started.
Waiting for timer...
Timer fired.
Timer duration: 2.00 seconds.
*/

编译代码

若要编译代码，请复制代码并将其粘贴到 wrl-consume-async.cpp 项目中或一个名为 parallel-matrix-multiply.cpp 的文件中，然后在命令提示符窗口中运行以下命令。

cl.exe wrl-consume-async.cpp runtimeobject.lib

示例：用后台线程处理

以下步骤启动辅助线程和定义该线程执行的操作。下面是完整的示例。

提示

此示例演示如何使用 ABI::Windows::Foundation::IAsyncAction 接口工作。可以将此模式应用与所有的接口实现 IAsyncInfo: IAsyncAction、IAsyncActionWithProgress、IAsyncOperation和 IAsyncOperationWithProgress。

包括 (#include) 任何必需的 Windows 运行时、WRL 或标准 C++ 库标头。

#include <Windows.Foundation.h>
#include <Windows.System.Threading.h>
#include <wrl/event.h>
#include <stdio.h>
#include <Objbase.h>

using namespace ABI::Windows::Foundation;
using namespace ABI::Windows::System::Threading;
using namespace Microsoft::WRL;
using namespace Microsoft::WRL::Wrappers;

Windows.System.Threading.h 声明需要辅助线程使用的类型。

我们建议您在 .cpp 文件中使用 using namespace 指令使代码更具可读性。

初始化 Windows 运行时。

// Initialize the Windows Runtime.
RoInitializeWrapper initialize(RO_INIT_MULTITHREADED);
if (FAILED(initialize))
{
    return PrintError(__LINE__, initialize);
}

创建接口的一个活动 ABI::Windows::System::Threading::IThreadPoolStatics 工厂。

// Get the activation factory for the IThreadPoolStatics interface.
ComPtr<IThreadPoolStatics> threadPool;
HRESULT hr = GetActivationFactory(HStringReference(RuntimeClass_Windows_System_Threading_ThreadPool).Get(), &threadPool);
if (FAILED(hr))
{
    return PrintError(__LINE__, hr);
}

创建事件对象同步对主应用程序的工作线程。

    // Create an event that is set after the timer callback completes. We later use this event to wait for the timer to complete.  
    // This event is for demonstration only in a console app. In most apps, you typically don't wait for async operations to complete.
    Event threadCompleted(CreateEventEx(nullptr, nullptr, CREATE_EVENT_MANUAL_RESET, WRITE_OWNER | EVENT_ALL_ACCESS));
    hr = threadCompleted.IsValid() ? S_OK : HRESULT_FROM_WIN32(GetLastError());
    if (FAILED(hr))
    {
        return PrintError(__LINE__, hr);
    }

备注

在控制台应用一部分，此事件只用于演示。此示例使用事件以确保可操作完成，在应用之前退出。在大多数应用，通常不可在等待操作完成。

调用 IThreadPoolStatics::RunAsync 方法创建辅助线程。使用 Callback 函数定义操作。

wprintf_s(L"Starting thread...\n");

// Create a thread that computes prime numbers.
ComPtr<IAsyncAction> asyncAction;
hr = threadPool->RunAsync(Callback<IWorkItemHandler>([&threadCompleted](IAsyncAction* asyncAction) -> HRESULT
{
    // Print a message. 
    const unsigned int start = 0;
    const unsigned int end = 100000;
    unsigned int primeCount = 0;
    for (int n = start; n < end; n++)
    {
        if (IsPrime(n))
        {
            primeCount++;
        }
    }

    wprintf_s(L"There are %u prime numbers from %u to %u.\n", primeCount, start, end);

    // Set the completion event and return.
    SetEvent(threadCompleted.Get());
    return S_OK;

}).Get(), &asyncAction);
if (FAILED(hr))
{
    return PrintError(__LINE__, hr);
}

IsPrime 函数在如下的完整示例中定义。

将消息打印到控制台并等待线程完成。所有 ComPtr 和 RAII 对象都离开范围并自动释放。

// Print a message and wait for the thread to complete.
wprintf_s(L"Waiting for thread...\n");

// Wait for the thread to complete.
WaitForSingleObjectEx(threadCompleted.Get(), INFINITE, FALSE);

wprintf_s(L"Finished.\n");

// All smart pointers and RAII objects go out of scope here.

这是完整示例:

// wrl-consume-asyncOp.cpp 
// compile with: runtimeobject.lib 
#include <Windows.Foundation.h>
#include <Windows.System.Threading.h>
#include <wrl/event.h>
#include <stdio.h>
#include <Objbase.h>

using namespace ABI::Windows::Foundation;
using namespace ABI::Windows::System::Threading;
using namespace Microsoft::WRL;
using namespace Microsoft::WRL::Wrappers;

// Prints an error string for the provided source code line and HRESULT 
// value and returns the HRESULT value as an int. 
int PrintError(unsigned int line, HRESULT hr)
{
    wprintf_s(L"ERROR: Line:%d HRESULT: 0x%X\n", line, hr);
    return hr;
}

// Determines whether the input value is prime. 
bool IsPrime(int n)
{
    if (n < 2)
    {
        return false;
    }
    for (int i = 2; i < n; ++i)
    {
        if ((n % i) == 0)
        {
            return false;
        }
    }
    return true;
}

int wmain()
{
    // Initialize the Windows Runtime.
    RoInitializeWrapper initialize(RO_INIT_MULTITHREADED);
    if (FAILED(initialize))
    {
        return PrintError(__LINE__, initialize);
    }

    // Get the activation factory for the IThreadPoolStatics interface.
    ComPtr<IThreadPoolStatics> threadPool;
    HRESULT hr = GetActivationFactory(HStringReference(RuntimeClass_Windows_System_Threading_ThreadPool).Get(), &threadPool);
    if (FAILED(hr))
    {
        return PrintError(__LINE__, hr);
    }

    // Create an event that is set after the timer callback completes. We later use this event to wait for the timer to complete.  
    // This event is for demonstration only in a console app. In most apps, you typically don't wait for async operations to complete.
    Event threadCompleted(CreateEventEx(nullptr, nullptr, CREATE_EVENT_MANUAL_RESET, WRITE_OWNER | EVENT_ALL_ACCESS));
    hr = threadCompleted.IsValid() ? S_OK : HRESULT_FROM_WIN32(GetLastError());
    if (FAILED(hr))
    {
        return PrintError(__LINE__, hr);
    }


    wprintf_s(L"Starting thread...\n");

    // Create a thread that computes prime numbers.
    ComPtr<IAsyncAction> asyncAction;
    hr = threadPool->RunAsync(Callback<IWorkItemHandler>([&threadCompleted](IAsyncAction* asyncAction) -> HRESULT
    {
        // Print a message. 
        const unsigned int start = 0;
        const unsigned int end = 100000;
        unsigned int primeCount = 0;
        for (int n = start; n < end; n++)
        {
            if (IsPrime(n))
            {
                primeCount++;
            }
        }

        wprintf_s(L"There are %u prime numbers from %u to %u.\n", primeCount, start, end);

        // Set the completion event and return.
        SetEvent(threadCompleted.Get());
        return S_OK;

    }).Get(), &asyncAction);
    if (FAILED(hr))
    {
        return PrintError(__LINE__, hr);
    }

    // Print a message and wait for the thread to complete.
    wprintf_s(L"Waiting for thread...\n");

    // Wait for the thread to complete.
    WaitForSingleObjectEx(threadCompleted.Get(), INFINITE, FALSE);

    wprintf_s(L"Finished.\n");

    // All smart pointers and RAII objects go out of scope here.
}
/*
Output:
Starting thread...
Waiting for thread...
There are 9592 prime numbers from 0 to 100000.
Finished.
*/

编译代码

若要编译代码，请复制代码并将其粘贴到 wrl-consume-asyncOp.cpp 项目中或一个名为 parallel-matrix-multiply.cpp 的文件中，然后在命令提示符窗口中运行以下命令。

cl.exe wrl-consume-asyncOp.cpp runtimeobject.lib

请参见

概念

Windows 运行时 C++ 模板库 (WRL)

通过

如何：使用 WRL 完成异步操作

示例：使用计时器的使用

编译代码

示例：用后台线程处理

编译代码

请参见

概念

其他资源