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.. data:: RLIM_INFINITY
46
47   Constant used to represent the limit for an unlimited resource.
48
49
50.. function:: getrlimit(resource)
51
52   Returns a tuple ``(soft, hard)`` with the current soft and hard limits of
53   *resource*. Raises :exc:`ValueError` if an invalid resource is specified, or
54   :exc:`error` if the underlying system call fails unexpectedly.
55
56
57.. function:: setrlimit(resource, limits)
58
59   Sets new limits of consumption of *resource*. The *limits* argument must be a
60   tuple ``(soft, hard)`` of two integers describing the new limits. A value of
61   :data:`~resource.RLIM_INFINITY` can be used to request a limit that is
62   unlimited.
63
64   Raises :exc:`ValueError` if an invalid resource is specified, if the new soft
65   limit exceeds the hard limit, or if a process tries to raise its hard limit.
66   Specifying a limit of :data:`~resource.RLIM_INFINITY` when the hard or
67   system limit for that resource is not unlimited will result in a
68   :exc:`ValueError`.  A process with the effective UID of super-user can
69   request any valid limit value, including unlimited, but :exc:`ValueError`
70   will still be raised if the requested limit exceeds the system imposed
71   limit.
72
73   ``setrlimit`` may also raise :exc:`error` if the underlying system call
74   fails.
75
76These symbols define resources whose consumption can be controlled using the
77:func:`setrlimit` and :func:`getrlimit` functions described below. The values of
78these symbols are exactly the constants used by C programs.
79
80The Unix man page for :manpage:`getrlimit(2)` lists the available resources.
81Note that not all systems use the same symbol or same value to denote the same
82resource.  This module does not attempt to mask platform differences --- symbols
83not defined for a platform will not be available from this module on that
84platform.
85
86
87.. data:: RLIMIT_CORE
88
89   The maximum size (in bytes) of a core file that the current process can create.
90   This may result in the creation of a partial core file if a larger core would be
91   required to contain the entire process image.
92
93
94.. data:: RLIMIT_CPU
95
96   The maximum amount of processor time (in seconds) that a process can use. If
97   this limit is exceeded, a :const:`SIGXCPU` signal is sent to the process. (See
98   the :mod:`signal` module documentation for information about how to catch this
99   signal and do something useful, e.g. flush open files to disk.)
100
101
102.. data:: RLIMIT_FSIZE
103
104   The maximum size of a file which the process may create.
105
106
107.. data:: RLIMIT_DATA
108
109   The maximum size (in bytes) of the process's heap.
110
111
112.. data:: RLIMIT_STACK
113
114   The maximum size (in bytes) of the call stack for the current process.  This only
115   affects the stack of the main thread in a multi-threaded process.
116
117
118.. data:: RLIMIT_RSS
119
120   The maximum resident set size that should be made available to the process.
121
122
123.. data:: RLIMIT_NPROC
124
125   The maximum number of processes the current process may create.
126
127
128.. data:: RLIMIT_NOFILE
129
130   The maximum number of open file descriptors for the current process.
131
132
133.. data:: RLIMIT_OFILE
134
135   The BSD name for :const:`RLIMIT_NOFILE`.
136
137
138.. data:: RLIMIT_MEMLOCK
139
140   The maximum address space which may be locked in memory.
141
142
143.. data:: RLIMIT_VMEM
144
145   The largest area of mapped memory which the process may occupy.
146
147
148.. data:: RLIMIT_AS
149
150   The maximum area (in bytes) of address space which may be taken by the process.
151
152
153Resource Usage
154--------------
155
156These functions are used to retrieve resource usage information:
157
158
159.. function:: getrusage(who)
160
161   This function returns an object that describes the resources consumed by either
162   the current process or its children, as specified by the *who* parameter.  The
163   *who* parameter should be specified using one of the :const:`RUSAGE_\*`
164   constants described below.
165
166   The fields of the return value each describe how a particular system resource
167   has been used, e.g. amount of time spent running is user mode or number of times
168   the process was swapped out of main memory. Some values are dependent on the
169   clock tick internal, e.g. the amount of memory the process is using.
170
171   For backward compatibility, the return value is also accessible as a tuple of 16
172   elements.
173
174   The fields :attr:`ru_utime` and :attr:`ru_stime` of the return value are
175   floating point values representing the amount of time spent executing in user
176   mode and the amount of time spent executing in system mode, respectively. The
177   remaining values are integers. Consult the :manpage:`getrusage(2)` man page for
178   detailed information about these values. A brief summary is presented here:
179
180   +--------+---------------------+-------------------------------+
181   | Index  | Field               | Resource                      |
182   +========+=====================+===============================+
183   | ``0``  | :attr:`ru_utime`    | time in user mode (float)     |
184   +--------+---------------------+-------------------------------+
185   | ``1``  | :attr:`ru_stime`    | time in system mode (float)   |
186   +--------+---------------------+-------------------------------+
187   | ``2``  | :attr:`ru_maxrss`   | maximum resident set size     |
188   +--------+---------------------+-------------------------------+
189   | ``3``  | :attr:`ru_ixrss`    | shared memory size            |
190   +--------+---------------------+-------------------------------+
191   | ``4``  | :attr:`ru_idrss`    | unshared memory size          |
192   +--------+---------------------+-------------------------------+
193   | ``5``  | :attr:`ru_isrss`    | unshared stack size           |
194   +--------+---------------------+-------------------------------+
195   | ``6``  | :attr:`ru_minflt`   | page faults not requiring I/O |
196   +--------+---------------------+-------------------------------+
197   | ``7``  | :attr:`ru_majflt`   | page faults requiring I/O     |
198   +--------+---------------------+-------------------------------+
199   | ``8``  | :attr:`ru_nswap`    | number of swap outs           |
200   +--------+---------------------+-------------------------------+
201   | ``9``  | :attr:`ru_inblock`  | block input operations        |
202   +--------+---------------------+-------------------------------+
203   | ``10`` | :attr:`ru_oublock`  | block output operations       |
204   +--------+---------------------+-------------------------------+
205   | ``11`` | :attr:`ru_msgsnd`   | messages sent                 |
206   +--------+---------------------+-------------------------------+
207   | ``12`` | :attr:`ru_msgrcv`   | messages received             |
208   +--------+---------------------+-------------------------------+
209   | ``13`` | :attr:`ru_nsignals` | signals received              |
210   +--------+---------------------+-------------------------------+
211   | ``14`` | :attr:`ru_nvcsw`    | voluntary context switches    |
212   +--------+---------------------+-------------------------------+
213   | ``15`` | :attr:`ru_nivcsw`   | involuntary context switches  |
214   +--------+---------------------+-------------------------------+
215
216   This function will raise a :exc:`ValueError` if an invalid *who* parameter is
217   specified. It may also raise :exc:`error` exception in unusual circumstances.
218
219   .. versionchanged:: 2.3
220      Added access to values as attributes of the returned object.
221
222
223.. function:: getpagesize()
224
225   Returns the number of bytes in a system page. (This need not be the same as the
226   hardware page size.)
227
228The following :const:`RUSAGE_\*` symbols are passed to the :func:`getrusage`
229function to specify which processes information should be provided for.
230
231
232.. data:: RUSAGE_SELF
233
234   :const:`RUSAGE_SELF` should be used to request information pertaining only to
235   the process itself.
236
237
238.. data:: RUSAGE_CHILDREN
239
240   Pass to :func:`getrusage` to request resource information for child processes of
241   the calling process.
242
243
244.. data:: RUSAGE_BOTH
245
246   Pass to :func:`getrusage` to request resources consumed by both the current
247   process and child processes.  May not be available on all systems.
248
249