Question

A process ID is a number that uniquely identifies a process. A process handle is also a number that uniquely identifys a process kernal object.

Why do we need them both since either of them can identify a process.

I think the answer may lie in the mapping relationship betweeen a process and a process kernel object. Is it true that more than one process kernel objects can be mapped to a single process? And each process kernel object has its own process handle. So that each of the process kernel object could represent different access mode or things like that.

This question came to me when I am using the MiniDumpWriteDump() function, which is declared like this:

BOOL WINAPI MiniDumpWriteDump(
  __in  HANDLE hProcess,
  __in  DWORD ProcessId,
  __in  HANDLE hFile,
  __in  MINIDUMP_TYPE DumpType,
  __in  PMINIDUMP_EXCEPTION_INFORMATION ExceptionParam,
  __in  PMINIDUMP_USER_STREAM_INFORMATION UserStreamParam,
  __in  PMINIDUMP_CALLBACK_INFORMATION CallbackParam
);

So it’s parameters include both process id and process handle. I just don’t know why it’s necessary to have them both.

Many thanks for your insights.

Answer 1

Process Handle is

1. Arbitrary
2. Internal to process that acquired it. Private and can’t be shared between threads/processes
3. It carries security access rights too

While Process ID is

1. Unique
2. Universal, public, so it can be shared between threads/processes