如何使用WaitForSingleObject

Question

为了试用如何使用Win32 API进行编程,我编写了一个创建进程的程序.然后我想检查我的进程是否等待新创建的进程,关闭句柄然后再次检查WaitForSingleObject(第二个进程正在休眠700毫秒)

第一个过程:

#include <iostream>
#include <windows.h>
#include <string>

using namespace std;

void main()
{
    bool ret;
    bool retwait;

    STARTUPINFO startupinfo;
    GetStartupInfo (&startupinfo);

    PROCESS_INFORMATION pro2info;

    wchar_t wcsCommandLine[] = L"D:\\betriebssystemePRA1PRO2.exe";

    ret = CreateProcess(NULL, wcsCommandLine, NULL, NULL, false, CREATE_NEW_CONSOLE, NULL,
                        NULL, &startupinfo, &pro2info);

    cout<<"hProcess: "<<pro2info.hProcess<<endl;
    cout<<"dwProcessId: "<<pro2info.dwProcessId <<endl;

    if (retwait= WaitForSingleObject (pro2info.hProcess, INFINITE)==true)
        cout<<"waitprocess:true"<<endl; //The process is finished
    else
        cout<<"waitprocess:false"<<endl;

    CloseHandle (pro2info.hProcess);//prozesshandle schließen, "verliert connection"

    if (retwait= WaitForSingleObject (pro2info.hProcess, INFINITE)==true) //When the process has finished
        cout<<"waitprocess:true"<<endl;
    else
        cout<<"waitprocess:false"<<endl;

    //cout<<GetLastError()<<endl; //Output the last error.

    ExitProcess(0);
}

第二个过程:

#include <iostream>
#include <windows.h>
#include <string>

using namespace std;

void main()
{
    int b;

    b = GetCurrentProcessId();

    cout << b << endl;
    cout << "Druecken Sie Enter zum Beenden" << endl;
    cin.get();
        //Wait until the user confirms

    Sleep (700);
    ExitProcess(0);

    cout<<"test";
}

第一个进程打印false,false; 但它应该打印为true,false.

而不是if-else语句,我使用了这个:

//switch(WaitForSingleObject (pro2info.hProcess, INFINITE)){
    //    case WAIT_OBJECT_0: cout << "ja";
    //        break;
    //    case WAIT_FAILED:cout << "nein";
    //        break;
    //    case WAIT_TIMEOUT:
    //        break;
    //}
//    cout<<"waitprocess:true"<<endl;//prozess ist fertig
//else
//    cout<<"waitprocess:false"<<endl;

这似乎有效.我的if-else陈述怎么办？

Answer 1

您真的需要注意API函数返回值的含义.您不能忽略CreateProcess()的FALSE返回.WaitForSingleObject()可以返回多个值,如果等待成功完成则返回0.这使你打印"假".

Answer 2

根据MSDN,如果等待没有中止,WaitForSingleObject将返回WAIT_OBJECT_0.如果您查看文档,则WAIT_OBJECT_0的值恰好是0x00000000L,这恰好是通常转换为的值false,而不是true.因此你的比较失败了.

推进的返回值WaitForSingleObject的bool是恕我直言,不是一个好主意,因为你得到指示,为什么等待过期几个潜在照明非零返回代码.

如果您仍希望将上述代码保留为使用布尔检查,请将测试更改为!WaitForSingleObject(...).