BSD::Resource - BSD process resource limit and priority functions


BSD::Resource - BSD process resource limit and priority functions


        use BSD::Resource;
        # the process resource consumption so far
        ($usertime, $systemtime,
         $maxrss, $ixrss, $idrss, $isrss, $minflt, $majflt, $nswap,
         $inblock, $oublock, $msgsnd, $msgrcv,
         $nsignals, $nvcsw, $nivcsw) = getrusage($ru_who);
        $rusage = getrusage($ru_who);
        # the process resource limits
        ($nowsoft, $nowhard) = getrlimit($resource);
        $rlimit = getrlimit($resource);
        $success = setrlimit($resource, $newsoft, $newhard);
        # the process scheduling priority
        $nowpriority = getpriority($pr_which, $pr_who);
        $success = setpriority($pr_which, $pr_who, $priority);
        # The following is not a BSD function.
        # It is a Perlish utility for the users of BSD::Resource.
        $rlimits = get_rlimits();



        ($usertime, $systemtime,
         $maxrss, $ixrss, $idrss, $isrss, $minflt, $majflt, $nswap,
         $inblock, $oublock, $msgsnd, $msgrcv,
         $nsignals, $nvcsw, $nivcsw) = getrusage($ru_who);
        $rusage = getrusage($ru_who);
        # $ru_who argument is optional; it defaults to RUSAGE_SELF
        $rusage = getrusage();

The $ru_who argument is either RUSAGE_SELF (the current process) or RUSAGE_CHILDREN (all the child processes of the current process) or it maybe left away in which case RUSAGE_SELF is used.

The RUSAGE_CHILDREN is the total sum of all the so far terminated (either successfully or unsuccessfully) child processes: there is no way to find out information about child processes still running.

On some systems (those supporting both getrusage() and the POSIX threads) there is also RUSAGE_THREAD. The BSD::Resource supports the RUSAGE_THREAD if it is present but understands nothing more about the POSIX threads themselves. Similarly for RUSAGE_BOTH: some systems support retrieving the sums of the self and child resource consumptions simultaneously.

In list context getrusage() returns the current resource usages as a list. On failure it returns an empty list.

The elements of the list are, in order:
indexnamemeaning usually (quite system dependent)

         0      utime           user time
         1      stime           system time
         2      maxrss          maximum shared memory or current resident set
         3      ixrss           integral shared memory
         4      idrss           integral or current unshared data
         5      isrss           integral or current unshared stack
         6      minflt          page reclaims
         7      majflt          page faults
         8      nswap           swaps
         9      inblock         block input operations
        10      oublock         block output operations
        11      msgsnd          messages sent
        12      msgrcv          messaged received
        13      nsignals        signals received
        14      nvcsw           voluntary context switches
        15      nivcsw          involuntary context switches

In scalar context getrusage() returns the current resource usages as a an object. The object can be queried via methods named exactly like the middle column, name, in the above table.

        $ru = getrusage();
        print $ru->stime, "\n";
        $total_context_switches = $ru->nvcsw + $ru->nivcsw;

For a detailed description about the values returned by getrusage() please consult your usual C programming documentation about getrusage() and also the header file <sys/resource.h>. (In Solaris, this might be <sys/rusage.h>).

Note 1: officially HP-UX does not support getrusage() at all but for the time being, it does seem to.

Note 2: Because not all kernels are BSD and also because of the sloppy support of getrusage() by many vendors many of the values may not be updated.

For example Solaris 1 claims in <sys/rusage.h> that the ixrss and the isrss fields are always zero.

In SunOS 5.5 and 5.6 the getrusage() leaves most of the fiels zero and therefore getrusage() is not even used, instead of that the /proc interface is used. The mapping is not perfect: the maxrss field is really the current resident size instead of the maximum, the idrss is really the current heap size instead of the integral data, the isrss is really the current stack size instead of the integral stack. The ixrss has no sensible counterpart at all so it stays zero.


        ($nowsoft, $nowhard) = getrlimit($resource);
        $rlimit = getrlimit($resource);

The $resource argument can be one of

        $resource               usual meaning           usual unit
        RLIMIT_CPU              CPU time                seconds
        RLIMIT_FSIZE            file size               bytes
        RLIMIT_DATA             data size               bytes
        RLIMIT_STACK            stack size              bytes
        RLIMIT_CORE             coredump size           bytes
        RLIMIT_RSS              resident set size       bytes
        RLIMIT_MEMLOCK          memory locked data size bytes
        RLIMIT_NPROC            number of processes     1
        RLIMIT_NOFILE           number of open files    1
        RLIMIT_OFILE            number of open files    1
        RLIMIT_OPEN_MAX         number of open files    1
        RLIMIT_AS               (virtual) address space bytes
        RLIMIT_VMEM             virtual memory (space)  bytes
        RLIMIT_TCACHE           maximum number of       1
                                cached threads
        RLIMIT_AIO_MEM          maximum memory locked   bytes
                                for POSIX AIO
        RLIMIT_AIO_OPS          maximum number          1
                                for POSIX AIO ops

What limits are available depends on the operating system. See below for get_rlimits() on how to find out which limits are available, for the exact documentation consult the documentation of your operatgiing system. The two groups (NOFILE, COFILE, <OPEN_MAX>) and (AS, VMEM) are aliases within themselves.

Two meta-resource-symbols might exist


RLIM_NLIMITS being the number of possible (but not necessarily fully supported) resource limits, see also the get_rlimits() call below. RLIM_INFINITY is useful in setrlimit(), the RLIM_INFINITY is represented as -1.

In list context getrlimit() returns the current soft and hard resource limits as a list. On failure it returns an empty list.

Processes have soft and hard resource limits. On crossing the soft limit they receive a signal (for example the SIGXCPU or SIGXFSZ, corresponding to the RLIMIT_CPU and RLIMIT_FSIZE, respectively). The processes can trap and handle some of these signals, please see Signals in the perlipc manpage. After the hard limit the processes will be ruthlessly killed by the KILL signal which cannot be caught.

NOTE: the level of 'support' for a resource varies. Not all the systems

        a) even recognise all those limits
        b) really track the consumption of a resource
        c) care (send those signals) if a resource limit is exceeded

Again, please consult your usual C programming documentation.

One notable exception for the better: officially HP-UX does not support getrlimit() at all but for the time being, it does seem to.

In scalar context getrlimit() returns the current soft and hard resource limits as an object. The object can be queried via methods cur and max, the current and maximum resource limits for the $resource, respectively.


        $nowpriority = getpriority($pr_which, $pr_who);
        # the default $pr_who is 0 (the current $pr_which)
        $nowpriority = getpriority($pr_which);
        # the default $pr_which is PRIO_PROCESS (the process priority)
        $nowpriority = getpriority();

getpriority() returns the current priority. NOTE: getpriority() can return zero or negative values completely legally. On failure getpriority() returns undef (and $! is set as usual).

The priorities returned by getpriority() are in the (inclusive) range PRIO_MIN...PRIO_MAX. The $pr_which argument can be any of PRIO_PROCESS (a process) PRIO_USER (a user), or PRIO_PGRP (a process group). The $pr_who argument tells which process/user/process group, 0 signifying the current one.

Usual values for PRIO_MIN, PRIO_MAX, are -20, 20. A negative value means better priority (more impolite process), a positive value means worse priority (more polite process).

NOTE: in AIX if the BSD compatibility library is not installed or not found by the installation procedure of the BSD::Resource the PRIO_MIN is 0 (corresponding to -20) and PRIO_MAX is 39 (corresponding to 19, the BSD priority 20 is unreachable).


        $success = setrlimit($resource, $newsoft, $newhard);

setrlimit() returns true on success and undef on failure.

NOTE: A normal user process can only lower its resource limits. Soft or hard limit RLIM_INFINITY means as much as possible, the real hard limits are normally buried inside the kernel and are very system-dependent.


        $success = setpriority($pr_which, $pr_who, $priority);
        # NOTE! If there are two arguments the second one is
        # the new $priority (not $pr_who) and the $pr_who is
        # defaulted to 0 (the current $pr_which)
        $success = setpriority($pr_which, $priority);
        # The $pr_who defaults to 0 (the current $pr_which) and
        # the $priority defaults to half of the PRIO_MAX, usually
        # that amounts to 10 (being a nice $pr_which).
        $success = setpriority($pr_which);
        # The $pr_which defaults to PRIO_PROCESS,
        $success = setpriority();

setpriority() is used to change the scheduling priority. A positive priority means a more polite process/process group/user; a negative priority means a more impoite process/process group/user. The priorities handled by setpriority() are [PRIO_MIN,PRIO_MAX]. A normal user process can only lower its priority (make it more positive).

NOTE: A successful call returns 1, a failed one 0.


        use BSD::Resource qw(times);
        ($user, $system, $child_user, $child_system) = times();

The BSD::Resource module offers a times() implementation that has usually slightly better time granularity than the times() by Perl core. The time granularity of the latter is usually 1/60 seconds while the former may achieve submilliseconds.

NOTE: The current implementation uses two getrusage() system calls: one with RUSAGE_SELF and one with RUSAGE_CHILDREN. Therefore the operation is not `atomic': the times for the children are recorded a little bit later.

NOTE: times() is not imported by default by BSD::Resource. You need to tell that you want to use it.

NOTE: This is not a real BSD function.


        $rlimits = get_rlimits();

NOTE: This is not a real BSD function. It is a convenience function.

get_rlimits() returns a reference to hash which has the names of the available resource limits as keys and their indices (those which are needed as the first argument to getrlimit() and setrlimit()) as values. For example:

        $r = get_rlimits();
        print "ok.\n" if ($r->{'RLIM_STACK'} == RLIM_STACK);



        # the user and system times so far by the process itself
        ($usertime, $systemtime) = getrusage();
        # ditto in OO way
        $ru = getrusage();
        $usertime   = $ru->utime;
        $systemtime = $ru->stime;
        # get the current priority level of this process
        $currprio = getpriority();


Copyright 1996-2002 Jarkko Hietaniemi All Rights Reserved

This library is free software; you may redistribute it and/or modify it under the same terms as Perl itself.


Jarkko Hietaniemi,

 BSD::Resource - BSD process resource limit and priority functions