Doc/lib/libresource.tex

   1 \section{\module{resource} ---
   2          Resource usage information}
   3
   4 \declaremodule{builtin}{resource}
   5   \platform{Unix}
   6 \modulesynopsis{An interface to provide resource usage information on
   7   the current process.}
   8 \moduleauthor{Jeremy Hylton}{jhylton@cnri.reston.va.us}
   9 \sectionauthor{Jeremy Hylton}{jhylton@cnri.reston.va.us}
  10
  11
  12 This module provides basic mechanisms for measuring and controlling
  13 system resources utilized by a program.
  14
  15 Symbolic constants are used to specify particular system resources and
  16 to request usage information about either the current process or its
  17 children.
  18
  19 A single exception is defined for errors:
  20
  21
  22 \begin{excdesc}{error}
  23   The functions described below may raise this error if the underlying
  24   system call failures unexpectedly.
  25 \end{excdesc}
  26
  27 \subsection{Resource Limits}
  28
  29 Resources usage can be limited using the \function{setrlimit()} function
  30 described below. Each resource is controlled by a pair of limits: a
  31 soft limit and a hard limit. The soft limit is the current limit, and
  32 may be lowered or raised by a process over time. The soft limit can
  33 never exceed the hard limit. The hard limit can be lowered to any
  34 value greater than the soft limit, but not raised. (Only processes with
  35 the effective UID of the super-user can raise a hard limit.)
  36
  37 The specific resources that can be limited are system dependent. They
  38 are described in the \manpage{getrlimit}{2} man page.  The resources
  39 listed below are supported when the underlying operating system
  40 supports them; resources which cannot be checked or controlled by the
  41 operating system are not defined in this module for those platforms.
  42
  43 \begin{funcdesc}{getrlimit}{resource}
  44   Returns a tuple \code{(\var{soft}, \var{hard})} with the current
  45   soft and hard limits of \var{resource}. Raises \exception{ValueError} if
  46   an invalid resource is specified, or \exception{error} if the
  47   underyling system call fails unexpectedly.
  48 \end{funcdesc}
  49
  50 \begin{funcdesc}{setrlimit}{resource, limits}
  51   Sets new limits of consumption of \var{resource}. The \var{limits}
  52   argument must be a tuple \code{(\var{soft}, \var{hard})} of two
  53   integers describing the new limits. A value of \code{-1} can be used to
  54   specify the maximum possible upper limit.
  55
  56   Raises \exception{ValueError} if an invalid resource is specified,
  57   if the new soft limit exceeds the hard limit, or if a process tries
  58   to raise its hard limit (unless the process has an effective UID of
  59   super-user).  Can also raise \exception{error} if the underyling
  60   system call fails.
  61 \end{funcdesc}
  62
  63 These symbols define resources whose consumption can be controlled
  64 using the \function{setrlimit()} and \function{getrlimit()} functions
  65 described below. The values of these symbols are exactly the constants
  66 used by \C{} programs.
  67
  68 The \UNIX{} man page for \manpage{getrlimit}{2} lists the available
  69 resources.  Note that not all systems use the same symbol or same
  70 value to denote the same resource.
  71
  72 \begin{datadesc}{RLIMIT_CORE}
  73   The maximum size (in bytes) of a core file that the current process
  74   can create.  This may result in the creation of a partial core file
  75   if a larger core would be required to contain the entire process
  76   image.
  77 \end{datadesc}
  78
  79 \begin{datadesc}{RLIMIT_CPU}
  80   The maximum amount of CPU time (in seconds) that a process can
  81   use. If this limit is exceeded, a \constant{SIGXCPU} signal is sent to
  82   the process. (See the \refmodule{signal} module documentation for
  83   information about how to catch this signal and do something useful,
  84   e.g. flush open files to disk.)
  85 \end{datadesc}
  86
  87 \begin{datadesc}{RLIMIT_FSIZE}
  88   The maximum size of a file which the process may create.  This only
  89   affects the stack of the main thread in a multi-threaded process.
  90 \end{datadesc}
  91
  92 \begin{datadesc}{RLIMIT_DATA}
  93   The maximum size (in bytes) of the process's heap.
  94 \end{datadesc}
  95
  96 \begin{datadesc}{RLIMIT_STACK}
  97   The maximum size (in bytes) of the call stack for the current
  98   process.
  99 \end{datadesc}
 100
 101 \begin{datadesc}{RLIMIT_RSS}
 102   The maximum resident set size that should be made available to the
 103   process.
 104 \end{datadesc}
 105
 106 \begin{datadesc}{RLIMIT_NPROC}
 107   The maximum number of processes the current process may create.
 108 \end{datadesc}
 109
 110 \begin{datadesc}{RLIMIT_NOFILE}
 111   The maximum number of open file descriptors for the current
 112   process.
 113 \end{datadesc}
 114
 115 \begin{datadesc}{RLIMIT_OFILE}
 116   The BSD name for \constant{RLIMIT_NOFILE}.
 117 \end{datadesc}
 118
 119 \begin{datadesc}{RLIMIT_MEMLOC}
 120   The maximm address space which may be locked in memory.
 121 \end{datadesc}
 122
 123 \begin{datadesc}{RLIMIT_VMEM}
 124   The largest area of mapped memory which the process may occupy.
 125 \end{datadesc}
 126
 127 \begin{datadesc}{RLIMIT_AS}
 128   The maximum area (in bytes) of address space which may be taken by
 129   the process.
 130 \end{datadesc}
 131
 132 \subsection{Resource Usage}
 133
 134 These functiona are used to retrieve resource usage information:
 135
 136 \begin{funcdesc}{getrusage}{who}
 137   This function returns a large tuple that describes the resources
 138   consumed by either the current process or its children, as specified
 139   by the \var{who} parameter.  The \var{who} parameter should be
 140   specified using one of the \constant{RUSAGE_*} constants described
 141   below.
 142
 143   The elements of the return value each
 144   describe how a particular system resource has been used, e.g. amount
 145   of time spent running is user mode or number of times the process was
 146   swapped out of main memory. Some values are dependent on the clock
 147   tick internal, e.g. the amount of memory the process is using.
 148
 149   The first two elements of the return value are floating point values
 150   representing the amount of time spent executing in user mode and the
 151   amount of time spent executing in system mode, respectively. The
 152   remaining values are integers. Consult the \manpage{getrusage}{2}
 153   man page for detailed information about these values. A brief
 154   summary is presented here:
 155
 156 \begin{tableii}{r|l}{code}{Offset}{Resource}
 157   \lineii{0}{time in user mode (float)}
 158   \lineii{1}{time in system mode (float)}
 159   \lineii{2}{maximum resident set size}
 160   \lineii{3}{shared memory size}
 161   \lineii{4}{unshared memory size}
 162   \lineii{5}{unshared stack size}
 163   \lineii{6}{page faults not requiring I/O}
 164   \lineii{7}{page faults requiring I/O}
 165   \lineii{8}{number of swap outs}
 166   \lineii{9}{block input operations}
 167   \lineii{10}{block output operations}
 168   \lineii{11}{messages sent}
 169   \lineii{12}{messages received}
 170   \lineii{13}{signals received}
 171   \lineii{14}{voluntary context switches}
 172   \lineii{15}{involuntary context switches}
 173 \end{tableii}
 174
 175   This function will raise a \exception{ValueError} if an invalid
 176   \var{who} parameter is specified. It may also raise
 177   \exception{error} exception in unusual circumstances.
 178 \end{funcdesc}
 179
 180 \begin{funcdesc}{getpagesize}{}
 181   Returns the number of bytes in a system page. (This need not be the
 182   same as the hardware page size.) This function is useful for
 183   determining the number of bytes of memory a process is using. The
 184   third element of the tuple returned by \function{getrusage()} describes
 185   memory usage in pages; multiplying by page size produces number of
 186   bytes.
 187 \end{funcdesc}
 188
 189 The following \constant{RUSAGE_*} symbols are passed to the
 190 \function{getrusage()} function to specify which processes information
 191 should be provided for.
 192
 193 \begin{datadesc}{RUSAGE_SELF}
 194   \constant{RUSAGE_SELF} should be used to
 195   request information pertaining only to the process itself.
 196 \end{datadesc}
 197
 198 \begin{datadesc}{RUSAGE_CHILDREN}
 199   Pass to \function{getrusage()} to request resource information for
 200   child processes of the calling process.
 201 \end{datadesc}
 202
 203 \begin{datadesc}{RUSAGE_BOTH}
 204   Pass to \function{getrusage()} to request resources consumed by both
 205   the current process and child processes.  May not be available on all
 206   systems.
 207 \end{datadesc}