Hi!
I am doing my project to develop a simple shell. I have a problem with handling signals that I hope you guys can help me.
I am using signal() function to catch the signal sending from the forked children to the shell, which is:
signal(SIGCHLD, handler);
However, this is really confusing. When the user input a command into my shell, normally the shell parse it and call the corresponding programs. However, when I have a pipe like:
ls | cat | cat | cat | cat > a.txt
Then there are multiple files running at once, and the signal handler does not seem to be able to catch multiple signal at one time...
I tried to use signal mask in my handler (in the code snippet).
But this does not seem help... I also applied the race running idea with signal suspend function to delay the moment the child return the signal but also, it does not work because I think at some moment, two child sends two SIGCHLDs at once, and that is really hard to control...
Right now, what I am doing is ask for the children to wait 1 second before sending any signals to the parent, and this works actually. But I don't think this is a smart way to handle signal...
I hope you can help me. Thank you!
Thank you!
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signal() is a really old interface and just not the best thing to use any more. Instead, you should use sigaction(). This call by default blocks block further signals of the type it is handling so you don't lose any. To write truly portable code, always use the sa_sigaction function, not the sa_handler (the spec of which can change between different unix variants). Also by default you don't have to reassert the handler every time it fires.
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by: rendaduiyanPosted on 2008-11-24 at 19:13:32ID: 23032208
have you ever counted how many times does your handller run?
are they matched?