Re: How to check if a thread waits for data at the read-end of a pipe?
From: Arkady Frenkel (arkadyf_at_hotmailxdotxcom)
Date: 11/25/04
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Date: Thu, 25 Nov 2004 11:17:35 +0200
If thread in waiting mode ( any ) you can use GetThreadContext()
Arkady
"Leif Erik Larsen" <leifel@online.no> wrote in message
news:Z8ipd.9526$rh1.241970@news2.e.nsc.no...
> After many tens of hours of searching Google, scanning programming
> groups, etc, I am almost about to give up. The only thing I have found
> is that there are (or at least has been) others struggling to find the
> answer to the same question as me, which makes me think that this is in
> fact something that is impossible, or at least difficult-, to do on
> Win32. So let me make some noice here once more, hopefully being more
> specific this time....
>
> I am about to port a C++ application (Larsen Commander) from OS/2 to
> Win32 and in the Win32 version I need a way to check (or get notified)
> when a thread or a process is waiting for data to be available at the
> read-end of my pipe. OS/2 has the API DosSetNPipeSem() that lets me
> attach a semaphore to a named pipe and I can then use the other API
> DosQueryNPipeSemState() to check if there is someone waiting at the
> read-end of the pipe. I guess Win32 has a way to let me do the same, but
> I am not able to find out how to do this using the standard Win32 SDK
> documentation. Anyone that can help?
>
> My application acts as a GUI command line shell in this regard. It has a
> console monitor and a command line where the user can launch internal
> and extarnal commands in the same way as with CMD.EXE. Larsen Commander
> launches command line programs as child processes, and redirects the
> child's STDIN, STDOUT and STDERR streams in standard documented ways.
> Everything works just great, except when it comes to one thing: When the
> child process attempts to read data from its STDIN it enters a
> wait-state because its STDIN-stream is empty. What I want to do in my
> application then is to show the command line in a special color mode, so
> the user can type some text of which to write to the pipe that feeds the
> childs STDIN. However, I find no way to check if there is someone at the
> read-end of the pipe waiting for data.
>
> Luckily (for my application and its users on Windows) most command line
> programs will never attempt to read anything from its STDIN, but some
> programs do. One example is UNZIP.EXE, which needs to get confirmations
> from the user (STDIN) e.g. before overwriting a file on the file system.
> UNZIP.EXE does this by reading from its STDIN.
>
> To be clear: The only information I need in order for this to work is a
> way to check if there is someone waiting for data at the read-end of my
> pipe.
>
> I am currently using an anonymous pipe created with Win32::CreatePipe(),
> but if I need to, and if it is possible, I can of course rewrite this to
> use a named pipe created with Win32:CreateNamedPipe(), or anything else.
> The best would be a way that is possible to work on all flavours of
> Win32, but it is also acceptible for me to use a technique only
> available on Win2000/XP.
>
> Remember: My application is a GUI application. Thus, I cannot use any
> console-based technique for this, as far as I can see.
>
> What I have tried are (code fragments only):
>
> 1) Using Win32::WaitForSingleObject() on the pipe file handle(s).
> ------------------------------------------------------------------
>
> // This doesn't seem to work (res will never be WAIT_TIMEOUT):
>
> HANDLE childStdInWriteSide = ...;
> HANDLE childStdInReadSide = ...;
> DWORD res = Win32::WaitForSingleObject(childStdInWriteSide, 0);
> if (res == WAIT_TIMEOUT) // If child wait for data at read-end?
> return true; // We never reach here! :-(
> else
> return false;
>
> // This doesn't work either (gives error "invalid handle"):
>
> HANDLE childStdInWriteSide = ...;
> HANDLE childStdInReadSide = ...;
> DWORD res = Win32::WaitForSingleObject(childStdInReadSide, 0);
> if (res == WAIT_TIMEOUT) // If child wait for data at read-end?
> return true; // We never reach here! :-(
> else
> return false;
>
> 2) Using Win32::NtQuerySystemInformation() to check the
> state of the child process thread(s).
> --------------------------------------------------------
>
> // This doesn't work (child process thread wait state
> // seems to be unstable).
>
> LPVOID infoBuff = ...;
> NtQuerySystemInformation(NT_PROCESSTHREAD_INFO, infoBuff, ...);
> PSYSTEM_PROCESSES p = (PSYSTEM_PROCESSES) infoBuff;
> for (;;)
> {
> if (p->ProcessId == myChildProcessInfo.dwProcessId)
> {
> // We have found the information for the child process of ours.
> int threadCount = p->ThreadCount;
> for (int i=0; i<threadCount; i++)
> {
> SYSTEM_THREADS* t = &p->Threads[i];
> if (t->State == StateWait &&
> (t->WaitReason == Executive ||
> t->WaitReason == WrLpcReply))
> {
> // This happens also when the thread is not actually
> // waiting on its STDIN, so I can't trust this.
> return true;
> }
> }
>
> // No need to test the remaining processes.
> break;
> }
> if (p->NextEntryDelta <= 0)
> break;
> p = (PSYSTEM_PROCESSES)((char*) p + p->NextEntryDelta);
> }
> return false;
>
> Thank you for reading all down to here. If you know I way to help me out
> of this problem I will be very, very happy.
>
> What about having a registration code of Larsen Commander for free? - To
> the person that first provides a solution that actually works!
>
> --
> Leif Erik Larsen
>
> Author of Larsen Commander
> Download for Windows and OS/2 available at
> http://home.online.no/~leifel/lcmd/index.html
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