windows C++- WRL 使用后台线程

由于WRL技术已经不作为主流继续发展，所以这里这个文档主要是收录WRL作为一些特殊情况下的查阅和理解windows体系开发的技术脉络，故本文档仅仅演示各项关键技术，例如本文档如何使用 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，而不是详细解释内部运行的机制。

本文档演示运行后台工作线程。此示例演示如何使用返回 IAsyncInfo 接口的 Windows 运行时方法。

示例：使用后台线程

以下步骤启动工作线程并定义该线程执行的操作。此示例演示如何使用 ABI::Windows::Foundation::IAsyncAction 接口。可以将此模式应用于实现 IAsyncInfo 的任何接口：IAsyncAction、IAsyncActionWithProgress、IAsyncOperation 和 IAsyncOperationWithProgress。

包括 (#include) 任何所需的 Windows 运行时、Windows 运行时 C++ 模板库或 C++ 标准库头文件。

#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 声明使用工作线程所需的类型。建议在 .cpp 文件中使用 using namespace 指令使代码更具可读性。

初始化 Windows 运行时库:

// Initialize the Windows Runtime.
RoInitializeWrapper initialize(RO_INIT_MULTITHREADED);
if (FAILED(initialize))
{
return PrintError(LINE, initialize);
}
为 ABI::Windows::System::Threading::IThreadPoolStatics 接口创建激活工厂。

// 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);
}
创建一个将工作线程的完成情况同步到主应用的 Event 对象。

// 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);
}
调用 IThreadPoolStatics::RunAsync 方法以创建工作线程。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);
}
将消息输出到控制台，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.

以下是完整代码:

// 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.
*/