Question

I am currently writing a program that will run mulitple programs in groups all at once and others on their own.


if( WAIT_FAILED == WaitForMultipleObjects(numberOfProgramsRan, &information[i].hProcess, TRUE, INFINITE) ) {
wcerr << L"Failure waiting for process" << endl;
}


numberOfProgramsRan is the number of programs that i ran in my loop.
&information[i] is a vector holding my process information from the create process

When i create the process in a for loop my program will wait if there are two or less processes being created (so two programs being passed in to run) before it runs my next processes.
If create more than two processes (or pass in more than two programs in my vector) my WaitForMultipleObjects it fails.

If i need to futher explain my issue please let me know.

Thanks for your help

Answer 1

If you only wait on a single process (index i) you should use WaitForSingleObject. If you’re waiting on multiple processes you need to pass in an array of handles as others have said – not a pointer into PROCESS_INFORMATION.
If you insist on using WaitFoRmultipleObjects for a single object use:

WaitForMultipleObjects(1, &information[i].hProcess, TRUE, INFINITE)

If you use anything other than 1 then look at the definition of PROCESS_INFORMATION:

typedef struct _PROCESS_INFORMATION {
  HANDLE hProcess;
  HANDLE hThread;
  DWORD  dwProcessId;
  DWORD  dwThreadId;
} PROCESS_INFORMATION, *LPPROCESS_INFORMATION;

The following dwProcessId and dwThreadID will then be incorrectly treated as handles your call will not work as expected.

Something like:

HANDLE hProcess[MAX_PROCESSES];
for(int i=0; i<numberOfProgramsRan; i++)
{
  hProcess[i] = information[i].hProcess;
}
WaitForMultipleObjects(numberOfProgramsRan, hProcess, TRUE, INFINITE);

Will wait on all your processes.