Strange SIGINT propagation between Parent/Child sh scripts Post: 302359361

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Top Forums Shell Programming and Scripting Strange SIGINT propagation between Parent/Child sh scripts Post 302359361 by danie.ludick on Tuesday 6th of October 2009 10:56:08 AM

10-06-2009

Registered User

Strange SIGINT propagation between Parent/Child sh scripts

Good day,

I am trying to add signal handling capabilities to some of my scripts. Unfortunately, I am having some difficulty with the manner in which signals are propagated between parent/child processes. Consider the following example:

I have the following "parent" script:

Code:

#!/usr/bin/sh

child_id=0

SIGINT_handler()
{
     echo "SIGINT caught in Parent"
     if [  $child_id  -ne 0 ]
         then
            echo Parent sendingi: kill -n 2 $child_id
            kill -n 2 $child_id
     fi
}


echo parent running
trap 'echo parent exiting; exit' 0
trap 'SIGINT_handler' 2                            # Pass Signal 2 to child but don't die
./child &
child_id=$!
echo 'child_id = ' $child_id

# Wait until child-process exits
wait $child_id
WAIT_STATUS=$?
echo Wait Status recorded when parent continues: $WAIT_STATUS

echo Parent Still Running after the child exits!
sleep 1000

which calls the following "child" script (as a background process):

Code:

#!/usr/bin/sh

echo child started. pid is $$
#trap 'echo child exiting; exit 0' 0
trap 'echo child got signal 2; exit 0' 2
sleep 1000

When I execute the "parent" process with a ">./parent",
I observe that the expected behavior. I then send a
SIGINT to the "parent" via a ">kill -s SIGINT <ppid>" and
get the following screen output:

Quote:

SIGINT caught in Parent
Parent sending: kill -n 2 20944
Wait Status recorded when parent continues: 130
Parent Still Running after the child exits!

When I look at the processes that are still active, I see
that the child (and its sleep) has not been killed at all -
all that happened was that the sleep-process of the parent
was activated.

I would appreciate it if anybody has some idea what is happening
here.

danie.ludick

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LEARN ABOUT SUNOS

preap

preap(1)							   User Commands							  preap(1)

NAME

       preap - force a defunct process to be reaped by its parent

SYNOPSIS

       preap [-F] pid...

DESCRIPTION

       A  defunct  (or	zombie)  process  is one whose exit status has yet to be reaped by its parent. The exit status is reaped via the wait(3C),
       waitid(2), or waitpid(3C) system call. In the normal course of system operation, zombies may occur, but are typically short-lived. This may
       happen  if a parent exits without having reaped the exit status of some or all of its children. In that case, those children are reparented
       to PID 1. See init(1M), which periodically reaps such processes.

       An irresponsible parent process may not exit for a very long time and thus leave zombies on the system. Since the operating system destroys
       nearly all components of a process before it becomes defunct, such defunct processes do not normally impact system operation. However, they
       do consume a small amount of system memory.

       preap forces the parent of the process specified by pid to waitid(3C) for pid, if pid represents a defunct process.

       preap will attempt to prevent the administrator from unwisely reaping a child process which might soon be reaped by the parent, if:

	 o  The process is a child of init(1M).

	 o  The parent process is stopped and might wait on the child when it is again allowed to run.

	 o  The process has been defunct for less than one minute.

OPTIONS

       The following option is supported:

       -F	Forces the parent to reap the child, overriding safety checks.

OPERANDS

       The following operand is supported:

       pid	Process ID list.

EXIT STATUS

       The following exit values are returned by preap, which prints the exit status of each target process reaped:

       0	Successfully operation.

       non-zero Failure, such as no such process, permission denied, or invalid option.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWesu (32-bit)		   |
       +-----------------------------+-----------------------------+
       |			     |SUNWesxu (64-bit) 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       proc(1), init(1M), waitid(2), wait(3C), waitpid(3C), proc(4), attributes(5)

WARNINGS

       preap should be applied sparingly and only in situations in which the administrator or developer has confirmed that defunct processes  will
       not be reaped by the parent process. Otherwise, applying preap may damage the parent process in unpredictable ways.

SunOS 5.10							    26 Mar 2001 							  preap(1)

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