Reading from a pipe without blocking the execution

ROOT
1

Hi,

I’m writing a GUI that basically controls the execution of other programs. I’ve used TSystem::OpenPipe to execute the program. Then, I read the pipe with TString::Gets and display it in the GUI with TGListBox::AddLine. Everything is simple and works very well, however, if the program running does not write a newline, the Gets method keeps waiting for it forever and blocks the execution of the program.

Is there a way to avoid this problem? Is there something like a signal that I can connect to a method of my GUI class that is raised when the pipe is ready to be read? If there is, how is this implemented in ROOT?

Thanks,

Rafael.

2

Hi,

TString::Gets() uses fgets() internally which does what you describe. You could simply call fgetc() yourself and add the characters to the TString.

Cheers, Axel.

3

Hi Axel,

Thanks for your reply. That partially solves my problem.

However, let’s say that the program is not filling the buffer at all, for instance, a simple “sleep” command. The GUI execution also halts.

I was looking for something as I described before, or even, simpler, a version of fgetc or fgets with a timeout. Does that exist?

Thanks again.

4

Hi,

okay, this is going a bit away from ROOT and more to generic C / C++… Google is usually pretty helpful with that. It shows e.g. ubuntuforums.org/showthread.php?t=936816

Cheers, Axel.

5

Thanks again Axel and sorry for the off-topic thread.

Very interesting this select() function, it’s all I needed and I ended up learning something new.