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Full Discussion: signal handler for SIGCHLD
Top Forums Programming signal handler for SIGCHLD Post 76778 by Perderabo on Thursday 30th of June 2005 01:13:18 PM
Old 06-30-2005
I would like to add that signals in unix are generally not queued despite some documentation to the contrary. So if 3 children exit while the parent is not running, it is not probable that the parent will receive 3 SIGCHLD signals. So the handler should be willing to loop to reap zero or more children.

I see that Posix seems to be blessing most of the System V SIGCHLD semantics:

Quote:
SA_NOCLDWAIT --If set, and sig equals SIGCHLD, child processes of the calling processes shall not be transformed into zombie processes when they terminate. If the calling process subsequently waits for its children, and the process has no unwaited-for children that were transformed into zombie processes, it shall block until all of its children terminate, and wait(), waitid(), and waitpid() shall fail and set errno to [ECHILD]. Otherwise, terminating child processes shall be transformed into zombie processes, unless SIGCHLD is set to SIG_IGN.
That's from the Posix sigaction man page. So properly ignoring the signal may be an option as well.
 

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PTHREAD_ATFORK(3)					   BSD Library Functions Manual 					 PTHREAD_ATFORK(3)

NAME
pthread_atfork -- register handlers to be called before and after fork() SYNOPSIS
#include <pthread.h> int pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void)); DESCRIPTION
The pthread_atfork() function declares fork handlers to be called before and after fork(2), in the context of the thread that called fork(2). The handlers registered with pthread_atfork() are called at the moments in time described below: prepare Before fork(2) processing commences in the parent process. If more than one prepare handler is registered they will be called in the opposite order they were registered. parent After fork(2) completes in the parent process. If more than one parent handler is registered they will be called in the same order they were registered. child After fork(2) processing completes in the child process. If more than one child handler is registered they will be called in the same order they were registered. If no handling is desired at one or more of these three points, a null pointer may be passed as the corresponding fork handler. Important: only async-signal-safe functions are allowed on the child side of fork(). See sigaction(2) for details. RETURN VALUES
If successful, the pthread_atfork() function will return zero. Otherwise an error number will be returned to indicate the error. ERRORS
The pthread_atfork() function will fail if: [ENOMEM] The system lacked the necessary resources to add another handler to the list. SEE ALSO
fork(2), pthread(3) STANDARDS
The pthread_atfork() conforms to ISO/IEC 9945-1:1996 (``POSIX.1''). BSD
June 21, 2004 BSD
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