本文主要是介绍windows C++- WRL 使用后台线程，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
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。
1. 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。
2. 初始化 Windows 运行时库:
// Initialize the Windows Runtime.
RoInitializeWrapper initialize(RO_INIT_MULTITHREADED);
if (FAILED(initialize))
{return PrintError(__LINE__, initialize);
}3. 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);
}4. 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);
}5. 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);
}6. 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.
*/这篇关于windows C++- WRL 使用后台线程的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！
