/Doc/library/resource.rst

  1
  2:mod:`resource` --- Resource usage information
  3==============================================
  4
  5.. module:: resource
  6   :platform: Unix
  7   :synopsis: An interface to provide resource usage information on the current process.
  8.. moduleauthor:: Jeremy Hylton <jeremy@alum.mit.edu>
  9.. sectionauthor:: Jeremy Hylton <jeremy@alum.mit.edu>
 10
 11
 12This module provides basic mechanisms for measuring and controlling system
 13resources utilized by a program.
 14
 15Symbolic constants are used to specify particular system resources and to
 16request usage information about either the current process or its children.
 17
 18A single exception is defined for errors:
 19
 20
 21.. exception:: error
 22
 23   The functions described below may raise this error if the underlying system call
 24   failures unexpectedly.
 25
 26
 27Resource Limits
 28---------------
 29
 30Resources usage can be limited using the :func:`setrlimit` function described
 31below. Each resource is controlled by a pair of limits: a soft limit and a hard
 32limit. The soft limit is the current limit, and may be lowered or raised by a
 33process over time. The soft limit can never exceed the hard limit. The hard
 34limit can be lowered to any value greater than the soft limit, but not raised.
 35(Only processes with the effective UID of the super-user can raise a hard
 36limit.)
 37
 38The specific resources that can be limited are system dependent. They are
 39described in the :manpage:`getrlimit(2)` man page.  The resources listed below
 40are supported when the underlying operating system supports them; resources
 41which cannot be checked or controlled by the operating system are not defined in
 42this module for those platforms.
 43
 44
 45.. function:: getrlimit(resource)
 46
 47   Returns a tuple ``(soft, hard)`` with the current soft and hard limits of
 48   *resource*. Raises :exc:`ValueError` if an invalid resource is specified, or
 49   :exc:`error` if the underlying system call fails unexpectedly.
 50
 51
 52.. function:: setrlimit(resource, limits)
 53
 54   Sets new limits of consumption of *resource*. The *limits* argument must be a
 55   tuple ``(soft, hard)`` of two integers describing the new limits. A value of
 56   ``-1`` can be used to specify the maximum possible upper limit.
 57
 58   Raises :exc:`ValueError` if an invalid resource is specified, if the new soft
 59   limit exceeds the hard limit, or if a process tries to raise its hard limit
 60   (unless the process has an effective UID of super-user).  Can also raise
 61   :exc:`error` if the underlying system call fails.
 62
 63These symbols define resources whose consumption can be controlled using the
 64:func:`setrlimit` and :func:`getrlimit` functions described below. The values of
 65these symbols are exactly the constants used by C programs.
 66
 67The Unix man page for :manpage:`getrlimit(2)` lists the available resources.
 68Note that not all systems use the same symbol or same value to denote the same
 69resource.  This module does not attempt to mask platform differences --- symbols
 70not defined for a platform will not be available from this module on that
 71platform.
 72
 73
 74.. data:: RLIMIT_CORE
 75
 76   The maximum size (in bytes) of a core file that the current process can create.
 77   This may result in the creation of a partial core file if a larger core would be
 78   required to contain the entire process image.
 79
 80
 81.. data:: RLIMIT_CPU
 82
 83   The maximum amount of processor time (in seconds) that a process can use. If
 84   this limit is exceeded, a :const:`SIGXCPU` signal is sent to the process. (See
 85   the :mod:`signal` module documentation for information about how to catch this
 86   signal and do something useful, e.g. flush open files to disk.)
 87
 88
 89.. data:: RLIMIT_FSIZE
 90
 91   The maximum size of a file which the process may create.  This only affects the
 92   stack of the main thread in a multi-threaded process.
 93
 94
 95.. data:: RLIMIT_DATA
 96
 97   The maximum size (in bytes) of the process's heap.
 98
 99
100.. data:: RLIMIT_STACK
101
102   The maximum size (in bytes) of the call stack for the current process.
103
104
105.. data:: RLIMIT_RSS
106
107   The maximum resident set size that should be made available to the process.
108
109
110.. data:: RLIMIT_NPROC
111
112   The maximum number of processes the current process may create.
113
114
115.. data:: RLIMIT_NOFILE
116
117   The maximum number of open file descriptors for the current process.
118
119
120.. data:: RLIMIT_OFILE
121
122   The BSD name for :const:`RLIMIT_NOFILE`.
123
124
125.. data:: RLIMIT_MEMLOCK
126
127   The maximum address space which may be locked in memory.
128
129
130.. data:: RLIMIT_VMEM
131
132   The largest area of mapped memory which the process may occupy.
133
134
135.. data:: RLIMIT_AS
136
137   The maximum area (in bytes) of address space which may be taken by the process.
138
139
140Resource Usage
141--------------
142
143These functions are used to retrieve resource usage information:
144
145
146.. function:: getrusage(who)
147
148   This function returns an object that describes the resources consumed by either
149   the current process or its children, as specified by the *who* parameter.  The
150   *who* parameter should be specified using one of the :const:`RUSAGE_\*`
151   constants described below.
152
153   The fields of the return value each describe how a particular system resource
154   has been used, e.g. amount of time spent running is user mode or number of times
155   the process was swapped out of main memory. Some values are dependent on the
156   clock tick internal, e.g. the amount of memory the process is using.
157
158   For backward compatibility, the return value is also accessible as a tuple of 16
159   elements.
160
161   The fields :attr:`ru_utime` and :attr:`ru_stime` of the return value are
162   floating point values representing the amount of time spent executing in user
163   mode and the amount of time spent executing in system mode, respectively. The
164   remaining values are integers. Consult the :manpage:`getrusage(2)` man page for
165   detailed information about these values. A brief summary is presented here:
166
167   +--------+---------------------+-------------------------------+
168   | Index  | Field               | Resource                      |
169   +========+=====================+===============================+
170   | ``0``  | :attr:`ru_utime`    | time in user mode (float)     |
171   +--------+---------------------+-------------------------------+
172   | ``1``  | :attr:`ru_stime`    | time in system mode (float)   |
173   +--------+---------------------+-------------------------------+
174   | ``2``  | :attr:`ru_maxrss`   | maximum resident set size     |
175   +--------+---------------------+-------------------------------+
176   | ``3``  | :attr:`ru_ixrss`    | shared memory size            |
177   +--------+---------------------+-------------------------------+
178   | ``4``  | :attr:`ru_idrss`    | unshared memory size          |
179   +--------+---------------------+-------------------------------+
180   | ``5``  | :attr:`ru_isrss`    | unshared stack size           |
181   +--------+---------------------+-------------------------------+
182   | ``6``  | :attr:`ru_minflt`   | page faults not requiring I/O |
183   +--------+---------------------+-------------------------------+
184   | ``7``  | :attr:`ru_majflt`   | page faults requiring I/O     |
185   +--------+---------------------+-------------------------------+
186   | ``8``  | :attr:`ru_nswap`    | number of swap outs           |
187   +--------+---------------------+-------------------------------+
188   | ``9``  | :attr:`ru_inblock`  | block input operations        |
189   +--------+---------------------+-------------------------------+
190   | ``10`` | :attr:`ru_oublock`  | block output operations       |
191   +--------+---------------------+-------------------------------+
192   | ``11`` | :attr:`ru_msgsnd`   | messages sent                 |
193   +--------+---------------------+-------------------------------+
194   | ``12`` | :attr:`ru_msgrcv`   | messages received             |
195   +--------+---------------------+-------------------------------+
196   | ``13`` | :attr:`ru_nsignals` | signals received              |
197   +--------+---------------------+-------------------------------+
198   | ``14`` | :attr:`ru_nvcsw`    | voluntary context switches    |
199   +--------+---------------------+-------------------------------+
200   | ``15`` | :attr:`ru_nivcsw`   | involuntary context switches  |
201   +--------+---------------------+-------------------------------+
202
203   This function will raise a :exc:`ValueError` if an invalid *who* parameter is
204   specified. It may also raise :exc:`error` exception in unusual circumstances.
205
206   .. versionchanged:: 2.3
207      Added access to values as attributes of the returned object.
208
209
210.. function:: getpagesize()
211
212   Returns the number of bytes in a system page. (This need not be the same as the
213   hardware page size.) This function is useful for determining the number of bytes
214   of memory a process is using. The third element of the tuple returned by
215   :func:`getrusage` describes memory usage in pages; multiplying by page size
216   produces number of bytes.
217
218The following :const:`RUSAGE_\*` symbols are passed to the :func:`getrusage`
219function to specify which processes information should be provided for.
220
221
222.. data:: RUSAGE_SELF
223
224   :const:`RUSAGE_SELF` should be used to request information pertaining only to
225   the process itself.
226
227
228.. data:: RUSAGE_CHILDREN
229
230   Pass to :func:`getrusage` to request resource information for child processes of
231   the calling process.
232
233
234.. data:: RUSAGE_BOTH
235
236   Pass to :func:`getrusage` to request resources consumed by both the current
237   process and child processes.  May not be available on all systems.
238