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Top Forums UNIX for Advanced & Expert Users retrieve process state programatically Post 302388724 by Andre_Merzky on Thursday 21st of January 2010 08:28:15 AM
Old 01-21-2010
Question retrieve process state programatically

Assume I spawn a process on (csh) command line, like

Code:
> du -a / >& /dev/null &

which creates a process with id 1234. Now, I can suspend/resume that process with

Code:
> kill -STOP 1234
> kill -CONT 1234

and can query the process state via 'jobs' or 'ps. How can I though query that state programatically (UNIX/POSIX system, no /proc/ available)?

The only call closest to the problem seems waitpid(), which can use WUNTRACED to get notifications on some signals, including SIGSTOP. That seems to work only for processes spawned within the same application - so I would not be able to write a tool which, for the example above, works like

Code:
> check_proc_state -p 1234
 1234 is Running

Another option is to do something like

Code:
FILE* fd = popen ("ps -ewwo pid=,uid=,state=,command=", "r");

and to grep the output - but ps output is not well standardized (well, it actually is, see ps, but the various implementations do not necessarily adhere to the spec), and also this seems a very cumbersome way to do that. Not to speak of performance...

Any better ideas? The solution ideally should work on MacOS, BSD, Linux, and AIX.

Thanks, Andre.


PS.: yes, I grep'ed the forum: huge amount of related posts, and I may well have missed relevant discussions in the noise. My apologies, and thanks for any pointers...

Last edited by Andre_Merzky; 01-21-2010 at 09:46 AM.. Reason: code tags, please...
 

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explain_waitpid_or_die(3)				     Library Functions Manual					 explain_waitpid_or_die(3)

NAME
explain_waitpid_or_die - wait for process to change state and report errors SYNOPSIS
#include <libexplain/waitpid.h> int pid = explain_waitpid_or_die(int pid, int *status, int options); DESCRIPTION
The explain_waitpid_or_die function is used to call the waitpid(2) system call. On failure an explanation will be printed to stderr, obtained from explain_waitpid(3), and then the process terminates by calling exit(EXIT_FAILURE). This function is intended to be used in a fashion similar to the following example: explain_waitpid_or_die(pid, status, options); pid The pid, exactly as to be passed to the waitpid(2) system call. status The status, exactly as to be passed to the waitpid(2) system call. options The options, exactly as to be passed to the waitpid(2) system call. Returns: This function only returns on success. On failure, prints an explanation and exits. SEE ALSO
waitpid(2) wait for process to change state explain_waitpid(3) explain waitpid(2) errors exit(2) terminate the calling process COPYRIGHT
libexplain version 0.52 Copyright (C) 2008 Peter Miller explain_waitpid_or_die(3)
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