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Operating Systems Linux does sending a signal cause task switching Post 302312355 by pfarre on Friday 1st of May 2009 03:09:59 AM
Old 05-01-2009
does sending a signal cause task switching

Hi all,

i am porting a system, that used to manipulate memory across processes using an interrupt handler - which means that upon return from the interrupt handler the memory change would be finished. I am trying to simulate this using signals on Linux 2.6.2x.

What i would like to know is wether sending a signal (ex. kill( pid , SIGUSR1 ) ) from a process will cause the kernel to perform taskswitching and put the calling process in queue, allowing the signal handler to run if it is ready?


A simplified scenario:
We have a shared memory area attached to both processes "share".

Process1:
...
share->variable = 0;
kill( Process2_pid , SIGUSR1 )
printf("share->variable= %d\n",share->variable);
...

Process2:
SIGUSR1_handler()
{
share->variable = 1;
}

It seems that the printf allways prints a "1" . Which would mean that taskswitching occurs, and that the handler in process2 has finished when process1 returns from kill().

But is this something one can rely on Running Linux 2.6.2x ?


Regards
Paul
 

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KILL(1) 						    BSD General Commands Manual 						   KILL(1)

NAME
kill -- terminate or signal a process SYNOPSIS
kill [-s signal_name] pid ... kill -l [exit_status] kill -signal_name pid ... kill -signal_number pid ... DESCRIPTION
The kill utility sends a signal to the processes specified by the pid operand(s). Only the super-user may send signals to other users' processes. The options are as follows: -s signal_name A symbolic signal name specifying the signal to be sent instead of the default TERM. -l [exit_status] If no operand is given, list the signal names; otherwise, write the signal name corresponding to exit_status. -signal_name A symbolic signal name specifying the signal to be sent instead of the default TERM. -signal_number A non-negative decimal integer, specifying the signal to be sent instead of the default TERM. The following pids have special meanings: -1 If superuser, broadcast the signal to all processes; otherwise broadcast to all processes belonging to the user. Some of the more commonly used signals: 1 HUP (hang up) 2 INT (interrupt) 3 QUIT (quit) 6 ABRT (abort) 9 KILL (non-catchable, non-ignorable kill) 14 ALRM (alarm clock) 15 TERM (software termination signal) Some shells may provide a builtin kill command which is similar or identical to this utility. Consult the builtin(1) manual page. SEE ALSO
builtin(1), csh(1), killall(1), ps(1), kill(2), sigaction(2) STANDARDS
The kill function is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible. HISTORY
A kill command appeared in Version 6 AT&T UNIX. BUGS
A replacement for the command ``kill 0'' for csh(1) users should be provided. BSD
April 28, 1995 BSD
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