how to discard instruction from previous signal Post: 302341899

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Top Forums Programming how to discard instruction from previous signal Post 302341899 by matrixmadhan on Friday 7th of August 2009 12:10:38 AM

08-07-2009

Registered User

Quote:

Originally Posted by Corona688

Well, you can't cancel signals that way. How about blocking them instead? You can make a signal wait in a queue until you're ready to deal with it with sigprocmask.

I see a potential problem (rare) with this approach, what if, when a file is being processed, signal 2 (2nd instance) is passed, since its blocked it will have to wait, while the first file is still being processed and if there are multiple instances of signals being queued ( due to the reason they are blocked ) ... that could be when there is an application bug that is indefinitely processing a file, without completing the signal handler, or closing a filehandle via possible stale NFS.

All these will have end up in having multiple signals in state " that are yet to be delivered "

---------- Post updated at 09:40 AM ---------- Previous update was at 09:34 AM ----------

Quote:

Originally Posted by nvhoang

Thank you all Corona688 and matrixmadhan for your replies,

Because I have 2 applications and need to make communication via files and signal.
The first application shall write some files then send a signal to the second application telling the second to processes and then delete those files.

The problem is that, when the second is processing those files, the first one may throw new files and signal (the goal is the second gets latest data); therefore the second might delete new files which leads to lost of data or to be consistent.

So I hope that, I could, when a signal comes the second restarts processing those files (and discard instructions from previous signal action). I know this is not nature of signal handling.

(I know that I can make it synchronously by making the second send back a signal to the first to tell that it is ready to receive new signal, for example).

Correct me if am wrong somewhere, please

these are the sequence of actions

first application processing is processing a file
processing done, first application sends a signal to second appln to initiate processing
second application starts processing
before 2nd could complete, first completes processing and makes 2nd file ready for processing, signals 2nd application.

Now, should 2nd application delete the first file and start processing the second file?

If that is the case, there could be a shared memory segment between 1st and 2nd application and make 2nd application to listen for any data contents in the shared memory segment, and based on the filename in the data segment process only that file and discard others.

matrixmadhan

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LEARN ABOUT LINUX

sgetmask

SGETMASK(2)						     Linux Programmer's Manual						       SGETMASK(2)

NAME

       sgetmask, ssetmask - manipulation of signal mask (obsolete)

SYNOPSIS

       long sgetmask(void);

       long ssetmask(long newmask);

DESCRIPTION

       These system calls are obsolete.  Do not use them; use sigprocmask(2) instead.

       sgetmask() returns the signal mask of the calling process.

       ssetmask() sets the signal mask of the calling process to the value given in newmask.  The previous signal mask is returned.

       The  signal  masks dealt with by these two system calls are plain bit masks (unlike the sigset_t used by sigprocmask(2)); use sigmask(3) to
       create and inspect these masks.

RETURN VALUE

       sgetmask() always successfully returns the signal mask.	ssetmask() always succeeds, and returns the previous signal mask.

ERRORS

       These system calls always succeed.

CONFORMING TO

       These system calls are Linux-specific.

NOTES

       Glibc does not provide wrappers for these system calls; use syscall(2).

       These system calls are unaware of signal numbers greater than 31 (i.e., real-time signals).

       It is not possible to block SIGSTOP or SIGKILL.

SEE ALSO

       sigprocmask(2), signal(7)

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2007-07-05							       SGETMASK(2)

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