900706 - how to get thread id?

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hi i need to post a message to a process from another process. i've written both processes. both are win32 console applications. for this purpose i need to use PostThreadMessage function.
1. is there another method for this purpose?
2. how can i know the thread id which i must provide for the function? i can provide the process id, but:
3. how can i obtain a thread id from a process id?
4. are they the same?
5. what happens if i use the process id as the thread id?
i tried to ask accurately. please give accurate answers (by numbers).
thx

Posted 27-Sep-11 22:22pm

ilostmyid2

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CPallini 28-Sep-11 8:48am

Did you create message queues?
Please have a look at:
http://blogs.msdn.com/b/oldnewthing/archive/2006/02/21/536055.aspx

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mbue · Answer 1 · 2011-09-28T05:48:00

Its impossible. You can only post messagees to threads they have a message queue. A process can have many threads - but threads have no names to distinguish them. So far as i know there isnt any function to enumerate all threads of a process - if there is one, to which thread you want to post the message?
Best solution (by my opinion) is to create an invisible dummy window. Then you can broadcast a registered message to communicate with the other process(es).
Regards.

[Edit]
apllication 1

C++

// application 1
void main()
{
  int    mterm = RegisterWindowMessage("MyTermMessage");
  HWND  hwnd = CreateWindowEx(0,__T("STATIC"),__T(""),0,0,0,0,0,0,0,0,0);
  for(MSG m;GetMessage(&m,0,0,0);DispatchMessage(&m))
  {
    if(mterm==m.message)
      PostQuitMessage(0);
  }
  DestroyWindow(hwnd);
}

application 2

C++

// application 2
void main()
{
  int            mterm = RegisterWindowMessage("MyTermMessage");
  unsigned long  to = BSM_APPLICATIONS;

  BroadcastSystemMessage(BSF_IGNORECURRENTTASK|BSF_POSTMESSAGE,&to,mterm,0,0);
}

You need a dummy window to receive the broadcasted message(s) - thats because you cannot post messages to unknown threads. As i explained - there is no function to get a thread id from another process.
Regards.

Madhu Nair · Answer 2 · 2011-09-27T23:01:00

I will suggest to use CreateNamedPipe to communicate with another non-windowed process rather than using the current design with PostThreadMessage. PostThreadMessage is helpful only inside a single process.
You can find more info from this MSDN page for CreateNamedPipe [^]and an example here[^].

ilostmyid2 · Answer 3 · 2011-09-28T20:16:00

Solution 5

i wrote the program like this:

C++

void main()
{
	MSG msg;
	while (GetMessage(&msg, 0, 0, 0))
	{
		TranslateMessage(&msg);
		if (msg.message == 101)
		{
			cout << "i got my msg!" << endl;
			PostQuitMessage(0);
		}
		else
			DispatchMessage(&msg);
	}
}

as u see it's a Win32 console application containing a msg loop. i think it consists of only one thread, the main thread. am i right? i need another process to post msg 101 to this process. that's all.
now what can i do? how the invisible window may help me?!
my solution so far has been to write the thread id by the process that wants to receive the msg to a file! like this code:

C++

DWORD thId = GetCurrentThreadId();
fprintf(fp, "%ld", thId);

then i run the process that wants to send the message. then it uses fscanf to read the thread id from the file and knows to what thread it has to post the msg, then calls PostThreadMessage!
any better suggestion? :)
i think PostThreadMessage, as Madhu said, is designed for sending msgs between threads inside a single process. but it's weird that there's no way to enumerate threads or get the main thread of a process!

Posted 28-Sep-11 20:16pm

ilostmyid2

Comments

[no name] 29-Sep-11 2:45am

A console application does not have a message queue! You will need to perform some hacktastic wizardry to force the NT kernel into calling PsConvertToGuiThread() You can accomplish this by invoking a win32k syscall with an index greater or equal to the NtGdiAbortDoc index. After you make the syscall the kernel will promote your main thread into a GUI thread, increase the stack size and give your thread a message queue.

ilostmyid2 29-Sep-11 3:05am

oh! there's no need for such a robust complicated method!
i just did it and it worked properly. i could get the output "i got my msg!" from this small program without doing it to give a GUI to it.
please re-read the text and try to re-think about it with this knowledge.
thx

[no name] 29-Sep-11 3:47am

Actually you are doing exactly as I described. When you call GetMessage() it invokes NtUserGetMessage which internally invokes a win32k syscall above 0x1000. But I guess that is besides the point. I apologize for complicating the issue, I did not fully read your question. I will try to answer all points:

1.) Yes.. there are many IPC techniques... pipes, memory maps... mailslots... sockets and the message subsystem are a few. Pick your poison.
2.) GetCurrentThreadId will get the current thread ID but it looks like you already know this. If you have a window handle and want to know both the thread ID and process id use GetWindowThreadProcessId()
3.) A process *can* have more than 1 thread. When the other program sends you a message... use GetWindowThreadProcessId to get both the thread ID and process ID from the window handle.
4.) No, a thread ID is not the same as a process ID.

Best Wishes,
-David Delaune

ilostmyid2 29-Sep-11 4:11am

thank u 4 ur reply,
let me concentrate on the original questions:
1. are console applications multi-threaded by default while i've not created any additional thread in them? (yes/no)!
2. how can i know the thread id of the process i have its id if it's single-threaded?
thx

[no name] 29-Sep-11 4:41am

1.) No, a process begins as a single thread.

2.) The question itself is nonsensical. A better question would be how to enumerate all threads belonging to the process. You could do something like:

#include <tlhelp32.h>
DWORD dwYourPIDToCompare = 0;
THREADENTRY32 te32;
te32.dwSize = sizeof(THREADENTRY32);

HANDLE hThreadSnap = CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD,0);
if(INVALID_HANDLE_VALUE != hThreadSnap)
{
if(Thread32First(hThreadSnap, &te32))
{
do
{
if(te32.th32OwnerProcessID == dwYourPIDToCompare)
{
//This thread belongs to the process
}
} while(Thread32Next(hThreadSnap, &te32));
CloseHandle(hThreadSnap);
}
}

mbue 29-Sep-11 7:01am

See my updated solution.
Please dont post your additional statements as solution, thanks.
Regards.

ilostmyid2 29-Sep-11 9:21am

thx, i think this must be the last solution.
u mean all threads regardless of the process they're belonging to must be enumerated and checked one after another to see which one's owner is the process i'm going to find its thread(s)?!
in another words, do ALL threads in the system currently running are walked in the above loop?!
is it really the last solution?

ilostmyid2 29-Sep-11 9:26am

another question:
in each process one thread is the main thread. that's the thread which has started the other threads and has begun running before other ones.
how can i find which one is it?
thx

[no name] 29-Sep-11 9:51am

I will try to answer both of questions:

1.) Yes the above code will iterate through all system threads. You should consider a process as a parent for many threads. 1 process can have many threads. There is no such thing as the 'main thread'. Anybody that tells you otherwise is wrong. Some software engineers will refer to the 'main thread' as the thread owning the top level window. However Microsoft Windows allows a process to have multiple top level windows.

2.) As I mentioned above the NT architecture does not have a 'main thread' for a process. However... if you want to be adventurous and consider the 'first thread' as the 'main thread' then you can use the code I previously gave you and call the GetThreadTimes function and read the lpCreationTime. The thread belonging to the process with the earliest creation time might be what you are looking for in most cases.

If you want to avoid enumerating ALL threads in the system... [REMOVED]
[UPDATE]
I removed the undocumented stuff. Don't bother with anything undocumented. You gain nothing from it. Even if you use NtQuerySystemInformation or NtQueryInformationProcess all it does is cause the kernel to iterate through these same internal linked lists internally. Just use the Toolhelp code above to enumerate process threads.

Best Wishes,
-David Delaune

ilostmyid2 29-Sep-11 10:53am

rehi
thank u in advance for such a great assistance. i wrote a code with ur advice. it's a console application which gets a process name as the only argument and gives its PID as well as all of its threads ids.
now, about ur answers:
i never talked about windows. in a win32 console application there's no window or top-level window. in all processes GetCurrentThreadId() returns a thread id, even though the process has never called CreateThread(). maybe it's called via the initialization functions run before calling main()? this is why no process exists that has no thread. am i right? is it possible that a process run without calling CreateThread()? in such a case i mean the first thread which was created by the process by main thread. the creation time is a good idea to find it.

[no name] 29-Sep-11 12:05pm

Congratulations,

I am happy to hear that you have worked it all out.

Yes you are correct. The NT kernel PE loader allocates and maps the PE image into an address space then walks through the InLoadOrderModuleList and maps/rebases/performs various other voodoo magic and eventually starts a single non-gui thread beginning execution at the AddressOfEntryPoint. When the thread performs the first GDI syscall it gets promoted into a GUI thread with a message queue.

I did not understand your second question. All usermode processes must have at least one thread or they will not be given any cpu time by the nt scheduler. A process without any executing threads are called zombie process.

Best Wishes,
-David Delaune

mbue · Answer 4 · 2011-09-29T06:11:00

Another solution:

C++

void PostMessageToProcessThreads(HANDLE hprocess,int msg)
{
  unsigned long  id = GetProcessId(hprocess);
  HANDLE        hs = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS|TH32CS_SNAPTHREAD,id);
  if(INVALID_HANDLE_VALUE!=hs)
  {
    THREADENTRY32  te = { sizeof(THREADENTRY32),0 };
    if(Thread32First(hs,&te))
    {
      do
      {
        if(id==te.th32OwnerProcessID)
        {
          if(te.th32ThreadID)
          {
            PostThreadMessage(te.th32ThreadID,msg,0,0);
          }
        }
      } while(Thread32Next(hs,&te));
    }
    CloseHandle(hs);
  }
}

Good luck.

900706 - how to get thread id?

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