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Trying to block signal

 
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Top Forums UNIX for Dummies Questions & Answers Trying to block signal
# 1  
Old 10-21-2010
Trying to block signal
I have this code that doesnt do what it is suppose to do. It should block signal that I send while process is running. I press control+z while this process is running and it should be blocked but it isnt. When i press control+z it gives me this....
[1]+ Stopped
When I change SIGTSP into SIGINT then it works as it should. I press control+c and it ignores it and continues executing my program.
Can anyone tell me why this is happening.

Code:
  sigset_t s;
  int j = 0;
  sigemptyset(&s);
  sigaddset(&first,SIGTSTP);

  for (i = 0 ; i < 10 ; i++){
     sleep(5);
     if ( sigprocmask(SIG_BLOCK,&first,NULL)==-1)
        break;

     fprintf("print something here\n");

  }

# 2  
Old 10-21-2010
Moderator's Comments:
Mod Comment Unix/Linux Man Pages are found here, on our site. Please use them in these forums.


Code:
KILL(1) 		      Linux User's Manual		       KILL(1)

NAME
       kill - send a signal to a process

SYNOPSIS
       kill [ -signal | -s signal ] pid ...
       kill [ -L | -V, --version ]
       kill -l	[ signal ]

DESCRIPTION
       The  default  signal  for  kill is TERM. Use -l or -L to list available
       signals.  Particularly useful signals include  HUP,  INT,  KILL,  STOP,
       CONT,  and  0.	Alternate  signals  may be specified in three ways: -9
       -SIGKILL -KILL.	Negative PID values may be used to choose  whole  pro-
       cess  groups;  see the PGID column in ps command output. A PID of -1 is
       special; it indicates all processes except the kill process itself  and
       init.

SIGNALS
       The  signals  listed  below  may  be available for use with kill.  When
       known constant, numbers and default behavior are shown.

       Name	Num   Action	Description
       ()									   ()

       0	  0   n/a	exit code indicates if a signal may be sent
       ALRM	 14   exit
       HUP	  1   exit
       INT	  2   exit
       KILL	  9   exit	this signal may not be blocked
       PIPE	 13   exit
       POLL	      exit
       PROF	      exit
       TERM	 15   exit
       USR1	      exit
       USR2	      exit
       VTALRM	      exit
       STKFLT	      exit	may not be implemented
       PWR	      ignore	may exit on some systems
       WINCH	      ignore
       CHLD	      ignore
       URG	      ignore
       TSTP	      stop	may interact with the shell
       TTIN	      stop	may interact with the shell
       TTOU	      stop	may interact with the shell
       STOP	      stop	this signal may not be blocked
 .
 .
 .
 .

# 3  
Old 10-22-2010
I have no idea what the relevence of DGPickett's post is.

The ctrl/z is being picked up by shell before it gets to your program. In foreground ctrl/z is commonly mapped to SUSP (suspend). The program can be brought to foreground with the "fg" Shell command.

To see the mapping of the various control keys in your session:
Code:
stty -a

Each and every one of these can (and often will) be disabled or changed to suit individual terminals or applications. See "man stty" for your O/S.

Many people re-map INTR to ctrl/c for consistency with MSDOS but on many terminals it is not mapped to anything by default.
This User Gave Thanks to methyl For This Post:
joker40
# 4  
Old 10-22-2010
One of the stop signals cannot be caught, something the kill not signal man page tells you. My very educational buddy truss/tusc tells us:
Code:
tusc -fap ksh -i

(p is a named pipe, so typing 'wc p' hangs blocked on open, and the cntrl-z stops it) that ^Z stty susp is SIGTSTP, which can be caught. You were blocking that signal, not SIGINT = cntrl-c usually. Maybe you need to catch it but do little? Else, Google 'UNIX signal tutorial' like I do at such times. Smilie
Moderator's Comments:
Mod Comment Unix/Linux Man Pages are found here, on our site. Please use them in these forums.

Code:
 .
 .
 .
[532] read(0, 0x400059b0, 1024) .......................... [sleeping]
wc p
[532] read(0, "w c   p \n", 1024) ........................ = 5
 .
 .
 .
[532] fork() ............................................. = 536
[536] fork() .......... (returning as child ...) ......... = 532
 .
 .
 .
[536] execve(0x40056b32, 0x400564ac, 0x4005677c) ......... [entry]
                              argv[0] @ 0x4005647d: "wc"
                              argv[1] @ 0x4005649d: "p"
[536] execve("/usr/bin/wc", 0x400564ac, 0x4005677c) ...... = 0 [32-bit]
 .
 .
 .
[536] open(0x7b0f0003, O_RDONLY|O_LARGEFILE, 0666) ....... [sleeping]
(^Z)
[532] waitpid(-1, WIFSTOPPED(SIGTSTP), WUNTRACED) ........ = 536
[532] sigvec(SIGCLD, 0x7b118258, 0x7b118268) ............. = 0
[532] waitpid(-1, WIFSTOPPED(SIGTSTP), WNOHANG|WUNTRACED)  = 0
[532] sigvec(SIGCLD, 0x7b118258, 0x7b118268) ............. = 0
[532] sigvec(SIGCLD, 0x7b118198, 0x7b1181a8) ............. = 0
[532] ioctl(2, TIOCGPGRP, 0x7b1181d0) .................... = 0
[532] ioctl(2, TIOCSPGRP, 0x7b118198) .................... = 0
[532] ioctl(2, TCSETATTRF, 0x40004e80) ................... = 0
[532] sigprocmask(SIG_BLOCK, 0x7b1180f0, 0x7b1180d0) ..... = 0
[532] sigprocmask(SIG_SETMASK, 0x7b1180d0, NULL) ......... = 0
[532] sigvec(SIGCLD, 0x7b117d98, 0x7b117da8) ............. = 0
[532] waitpid(-1, WIFSTOPPED(SIGTSTP), WNOHANG|WUNTRACED)  = 0
[532] sigvec(SIGCLD, 0x7b117d98, 0x7b117da8) ............. = 0
[532] lseek(2047, 864312, SEEK_SET) ...................... = 864312
[532] sigprocmask(SIG_BLOCK, 0x7b117f30, 0x7b117f10) ..... = 0
[532] read(2047, "w c   p \n\0", 1024) ................... = 6
[532] sigprocmask(SIG_SETMASK, 0x7b117f10, NULL) ......... = 0
[532] time(0x7b117c50) ................................... = 1287760639
[532] lseek(2047, 864318, SEEK_SET) ...................... = 864318
[532] sigprocmask(SIG_BLOCK, 0x7b117db0, 0x7b117d90) ..... = 0
[532] read(2047, 0x40055c98, 1024) ....................... = 0
[532] sigprocmask(SIG_SETMASK, 0x7b117d90, NULL) ......... = 0
[532] ioctl(0, TIOCGWINSZ, 0x7b117d10) ................... = 0
[1] + Stopped                  wc p
$ [532] write(2, "[ 1 ]   +   S t o p p e d       ".., 38) . = 38
[532] sigvec(SIGCLD, 0x7b117ed8, 0x7b117ee8) ............. = 0
[532] waitpid(-1, WIFSTOPPED(SIGTSTP), WNOHANG|WUNTRACED)  = 0
[532] sigvec(SIGCLD, 0x7b117ed8, 0x7b117ee8) ............. = 0
[532] sigprocmask(SIG_BLOCK, 0x7b117db0, 0x7b117d90) ..... = 0
[532] read(0, 0x400059b0, 1024) .......................... [sleeping]

Code:
$ stty -a
speed 9600 baud; line = 0; 
rows = 25; columns = 80
min = 4; time = 0; 
intr = ^C; quit = ^\; erase = ^H; kill = ^U
eof = ^D; eol = ^@; eol2 <undef>; swtch = ^@
stop = ^S; start = ^Q; susp = ^Z; dsusp <undef>
werase <undef>; lnext <undef>
-parenb -parodd cs8 -cstopb hupcl cread -clocal -loblk -crts 
-ignbrk brkint ignpar -parmrk -inpck istrip -inlcr -igncr icrnl -iuclc 
ixon ixany ixoff -imaxbel -rtsxoff -ctsxon -ienqak 
isig icanon -iexten -xcase echo echoe echok -echonl -noflsh 
-echoctl -echoprt -echoke -flusho -pendin 
opost -olcuc onlcr -ocrnl -onocr -onlret -ofill -ofdel -tostop 
$



---------- Post updated at 11:53 AM ---------- Previous update was at 11:49 AM ----------




PS:

Introduction To Unix Signals Programming

Note: Older systems do not support the sigprocmask() system call. Instead, one should use the sigmask() and sigsetmask() system calls. If you have such an operating system handy, please read the manual pages for these system calls. They are simpler to use than sigprocmask, so it shouldn't be too hard understanding them once you've read this section.
These 2 Users Gave Thanks to DGPickett For This Post:
joker40 methyl
# 5  
Old 10-22-2010
Note: Unix and Linux Man Pages are found on our site, these forums, please use them when you post here. Ours are better anyway!

Moderator's Comments:
Mod Comment Unix/Linux Man Pages are found here, on our site. Please use them in these forums.
# 6  
Old 10-22-2010
@joker40
What is the output from this command on your system?
Code:
stty -a

 
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