Get the PID of the process started by CreateProcess() - c

Question

Let me start off by stating that I'm not from C background. I'm a PHP developer. So everything that I've coded so far is by taking bits and pieces from other examples and fine tuning them to meet my requirements. So please bear with me if I ask way too basic or obvious questions.
I'm starting FFmpeg using CreateProcess() through
int startFFmpeg()
{
snprintf(cmd, sizeof(cmd), "D:\\ffpmeg\bin\ffmpeg.exe -i D:\\video.mpg -r 10 D:\\frames");
PROCESS_INFORMATION pi;
STARTUPINFO si={sizeof(si)};
si.cb = sizeof(STARTUPINFO);
int ff = CreateProcess(NULL, cmd, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi);
return ff;
}
What I need to do is get the PID of that process and then check later to see if it still running after some time. This is basically what I'm looking for:
int main()
{
int ff = startFFmpeg();
if(ff)
{
// great! FFmpeg is generating frames
// then some time later
if(<check if ffmpeg is still running, probably by checking the PID in task manager>) // <-- Need this condition
{
// if running, continue
}
else
{
startFFmpeg();
}
}
return 0;
}
I did some research and found out that PID is returned within the PROCESS_INFORMATION, but I couldn't find an example showing how to fetch it.
Some metadata
OS : Windows 7
Language : C
IDE : Dev C++

Answer 1

Pull it from the PROCESS_INFORMATION structure you pass as the last parameter to CreateProcess(), in your case pi.dwProcessId
However, to check if it is still running, you may want to just wait on the process handle.
static HANDLE startFFmpeg()
{
snprintf(cmd, sizeof(cmd), "D:\\ffpmeg\bin\ffmpeg.exe -i D:\\video.mpg -r 10 D:\\frames");
PROCESS_INFORMATION pi = {0};
STARTUPINFO si = {0};
si.cb = sizeof(STARTUPINFO);
if (CreateProcess(NULL, cmd, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi))
{
CloseHandle(pi.hThread);
return pi.hProcess;
}
return NULL;
}
In your launching main() you can then do something like...
int main()
{
HANDLE ff = startFFmpeg();
if(ff != NULL)
{
// wait with periodic checks. this is setup for
// half-second checks. configure as you need
while (WAIT_TIMEOUT == WaitForSingleObject(ff, 500))
{
// your wait code goes here.
}
// close the handle no matter what else.
CloseHandle(ff);
}
return 0;
}

Answer 2

You might like to use the win32 api function GetProcessId().
#include <windows.h>
...
BOOL bSuccess = FALSE;
LPTSTR pszCmd = NULL;
PROCESS_INFORMATION pi = {0};
STARTUPINFO si = {0};
si.cb = sizeof(si);
pszCmd = ... /* assign something useful */
bSuccess = CreateProcess(NULL, pszCmd, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi);
if (bSuccess)
{
DWORD dwPid = GetProcessId(pi.hProcess);
...
}
else
... /* erorr handling */
For details please see here: http://msdn.microsoft.com/en-us/library/windows/desktop/ms683215%28v=vs.85%29.aspx