Question

I faced with strange behavior of function GetProcessHandleCount().
At first I take a snapshot of all processes in the system as it is described in msdn:

HANDLE hProcessSnap;
HANDLE hProcess;
PROCESSENTRY32 pe32;
hProcessSnap = CreateToolhelp32Snapshot( TH32CS_SNAPPROCESS, 0 );
pe32.dwSize = sizeof( PROCESSENTRY32 );
if( !Process32First( hProcessSnap, &pe32 ) )
  {
      CloseHandle( hProcessSnap );
      return 0;
  }

Then I walk the snapshot of processes, and count up open handles by using function
GetProcessHandleCount:

 int count_of_handles=0; 
 DWORD dwHandleCount=0; 
 do {
    hProcess = OpenProcess( PROCESS_QUERY_INFORMATION,FALSE,pe32.th32ProcessID);
    GetProcessHandleCount(hProcess,&dwHandleCount); 
    count_of_handles+=dwHandleCount;  
    if( hProcess != NULL ) 
        CloseHandle( hProcess );
  } while( Process32Next( hProcessSnap, &pe32 ) );

I checked this program in Windows 7 x64. Program displayed count_of_handles ~16000, but really this value was ~100 000 (if believe in Windows Task Manager).
Then I executed this program in Windows XP x32 (by VMWare), and count_of_handles was ~9000 (but in real it was ~8000).
What is wrong with my code? Thank you.

Answer 1

For one thing, GetProcessHandleCount might return zero (which signifies an error). This could explain coming to a result lower than what you expect. This might be caused in turn by OpenProcess failing (you don’t check for that either).