How to count processes starting with the full file name?

Question

I am trying to get a process count starting with the full name of the executable.

Here is my code:

function GetPathFromPID(const PID: cardinal): string;
var
  hProcess: THandle;
  path: array[0..MAX_PATH - 1] of char;
begin
  hProcess := OpenProcess(PROCESS_QUERY_INFORMATION or PROCESS_VM_READ, false, PID);
  if hProcess <> 0 then
    try
      if GetModuleFileNameEx(hProcess, 0, path, MAX_PATH) = 0 then
        RaiseLastOSError;
      result := path;
    finally
      CloseHandle(hProcess)
    end
  else
    RaiseLastOSError;
end;

function ProcessCount(const AFullFileName: string): Integer;
var
  ContinueLoop: boolean;
  FSnapshotHandle: THandle;
  FProcessEntry32: TProcessEntry32;
begin
  FSnapshotHandle := CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
  FProcessEntry32.dwSize := SizeOf(FProcessEntry32);
  ContinueLoop := Process32First(FSnapshotHandle, FProcessEntry32);
  Result := 0;
  while(ContinueLoop) do
  begin
    if ((UpperCase(GetPathFromPID(FProcessEntry32.th32ProcessID)) = UpperCase(AFullFileName)))
    then Result := Result + 1;
    ContinueLoop := Process32Next(FSnapshotHandle, FProcessEntry32);
  end;
  CloseHandle(FSnapshotHandle);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Self.Caption := IntToStr(ProcessCount(Application.ExeName));
end;

GetPathFromPIDthe function was taken from here (answer by Andreas Regbrand).

Running the application, I got an EOSError exception ('System Error. Code: 87.'). As the documentation says:

ERROR_INVALID_PARAMETER

87 (0x57)

Invalid parameter.

An exception arises from the function GetPathFromPIDbecause the condition hProcess <> 0fails and is satisfied RaiseLastOSError.

Debugging I noticed that 0 is passed to the function GetPathFromPIDas a PID parameter, but I don't understand what is wrong in my code.

Answer 1

OpenProcess ERROR_INVALID_PARAMETER, PID .

ERROR_ACCESS_DENIED, , OpenProcess GetPathFromPID, .

, , .

  while (ContinueLoop) do
  begin
    if SameText(ExtractFileName(AFullFileName), FProcessEntry32.szExeFile) then
    if ((UpperCase(GetPathFromPID(FProcessEntry32.th32ProcessID)) = UpperCase(AFullFileName)))
     ....
  end;

Answer 2

, FProcessEntry32.th32ProcessID 0.

, [System Process] (check FProcessEntry32.szExeFile) PID 0. , th32ProcessID == 0. . " " .

, FProcessEntry32.th32ProcessID <> 0, GetPathFromPID.