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Programming
Catching signal and piping
Post 89493 by joseph_ng on Monday 14th of November 2005 12:24:36 AM
11-14-2005
I run through my system's source codes and I notice that this is often done for application programs or process that uses motif but it is also used for some other processes that perform serial port communication. Recently, I have written a motif application for a GSM server and I am also using their piping methods but now I am questioning the purpose/wisdom of doing it.
Its basically a 5 steps procedure
1)Do the standard signal declarations
2)Open a pipe
3)Create a signal handler for a particular signal eg SigUSR1
4)If the handler is provoked, write something(can be anything) into the pipe, chain the old handlers
5)Read the pipe and if there is something in there, do something, mostly cross-server processes.
Isn't it easier to use the standard signal handlers and do a case statement to decide what to do for each received signals?
Is it possible that the original authors wanted to avoid too much handling codes for different signals so they decided to simply create a pipe for single signal handling? I believe they are doing this for some good reasons because they are doing this for almost all the processes. I may sounds a bit stubborn but I am really very curious and very interested to get an answer for this.
I have tried to ask one of them(there are not many left) but he could not give me a good answer
Its basically a 5 steps procedure
1)Do the standard signal declarations
2)Open a pipe
3)Create a signal handler for a particular signal eg SigUSR1
4)If the handler is provoked, write something(can be anything) into the pipe, chain the old handlers
5)Read the pipe and if there is something in there, do something, mostly cross-server processes.
Isn't it easier to use the standard signal handlers and do a case statement to decide what to do for each received signals?
Is it possible that the original authors wanted to avoid too much handling codes for different signals so they decided to simply create a pipe for single signal handling? I believe they are doing this for some good reasons because they are doing this for almost all the processes. I may sounds a bit stubborn but I am really very curious and very interested to get an answer for this.
I have tried to ask one of them(there are not many left) but he could not give me a good answer
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LEARN ABOUT DEBIAN
sysv_signal
SYSV_SIGNAL(3) Linux Programmer's Manual SYSV_SIGNAL(3) NAME
sysv_signal - signal handling with System V semantics SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <signal.h> typedef void (*sighandler_t)(int); sighandler_t sysv_signal(int signum, sighandler_t handler); DESCRIPTION
The sysv_signal() function takes the same arguments, and performs the same task, as signal(2). However sysv_signal() provides the System V unreliable signal semantics, that is: a) the disposition of the signal is reset to the default when the handler is invoked; b) delivery of further instances of the signal is not blocked while the signal handler is executing; and c) if the handler interrupts (certain) blocking system calls, then the system call is not automatically restarted. RETURN VALUE
The sysv_signal() function returns the previous value of the signal handler, or SIG_ERR on error. ERRORS
As for signal(2). CONFORMING TO
This function is nonstandard. NOTES
Use of sysv_signal() should be avoided; use sigaction(2) instead. On older Linux systems, sysv_signal() and signal(2) were equivalent. But on newer systems, signal(2) provides reliable signal semantics; see signal(2) for details. The use of sighandler_t is a GNU extension; this type is only defined if the _GNU_SOURCE feature test macro is defined. SEE ALSO
sigaction(2), signal(2), bsd_signal(3), signal(7) COLOPHON
This page is part of release 3.44 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/. 2007-05-04 SYSV_SIGNAL(3)