1:mod:`resource` --- Resource usage information 2============================================== 3 4.. module:: resource 5 :platform: Unix 6 :synopsis: An interface to provide resource usage information on the current process. 7 8.. moduleauthor:: Jeremy Hylton <jeremy@alum.mit.edu> 9.. sectionauthor:: Jeremy Hylton <jeremy@alum.mit.edu> 10 11-------------- 12 13This module provides basic mechanisms for measuring and controlling system 14resources utilized by a program. 15 16Symbolic constants are used to specify particular system resources and to 17request usage information about either the current process or its children. 18 19An :exc:`OSError` is raised on syscall failure. 20 21 22.. exception:: error 23 24 A deprecated alias of :exc:`OSError`. 25 26 .. versionchanged:: 3.3 27 Following :pep:`3151`, this class was made an alias of :exc:`OSError`. 28 29 30Resource Limits 31--------------- 32 33Resources usage can be limited using the :func:`setrlimit` function described 34below. Each resource is controlled by a pair of limits: a soft limit and a hard 35limit. The soft limit is the current limit, and may be lowered or raised by a 36process over time. The soft limit can never exceed the hard limit. The hard 37limit can be lowered to any value greater than the soft limit, but not raised. 38(Only processes with the effective UID of the super-user can raise a hard 39limit.) 40 41The specific resources that can be limited are system dependent. They are 42described in the :manpage:`getrlimit(2)` man page. The resources listed below 43are supported when the underlying operating system supports them; resources 44which cannot be checked or controlled by the operating system are not defined in 45this module for those platforms. 46 47 48.. data:: RLIM_INFINITY 49 50 Constant used to represent the limit for an unlimited resource. 51 52 53.. function:: getrlimit(resource) 54 55 Returns a tuple ``(soft, hard)`` with the current soft and hard limits of 56 *resource*. Raises :exc:`ValueError` if an invalid resource is specified, or 57 :exc:`error` if the underlying system call fails unexpectedly. 58 59 60.. function:: setrlimit(resource, limits) 61 62 Sets new limits of consumption of *resource*. The *limits* argument must be a 63 tuple ``(soft, hard)`` of two integers describing the new limits. A value of 64 :data:`~resource.RLIM_INFINITY` can be used to request a limit that is 65 unlimited. 66 67 Raises :exc:`ValueError` if an invalid resource is specified, if the new soft 68 limit exceeds the hard limit, or if a process tries to raise its hard limit. 69 Specifying a limit of :data:`~resource.RLIM_INFINITY` when the hard or 70 system limit for that resource is not unlimited will result in a 71 :exc:`ValueError`. A process with the effective UID of super-user can 72 request any valid limit value, including unlimited, but :exc:`ValueError` 73 will still be raised if the requested limit exceeds the system imposed 74 limit. 75 76 ``setrlimit`` may also raise :exc:`error` if the underlying system call 77 fails. 78 79 VxWorks only supports setting :data:`RLIMIT_NOFILE`. 80 81.. function:: prlimit(pid, resource[, limits]) 82 83 Combines :func:`setrlimit` and :func:`getrlimit` in one function and 84 supports to get and set the resources limits of an arbitrary process. If 85 *pid* is 0, then the call applies to the current process. *resource* and 86 *limits* have the same meaning as in :func:`setrlimit`, except that 87 *limits* is optional. 88 89 When *limits* is not given the function returns the *resource* limit of the 90 process *pid*. When *limits* is given the *resource* limit of the process is 91 set and the former resource limit is returned. 92 93 Raises :exc:`ProcessLookupError` when *pid* can't be found and 94 :exc:`PermissionError` when the user doesn't have ``CAP_SYS_RESOURCE`` for 95 the process. 96 97 .. availability:: Linux 2.6.36 or later with glibc 2.13 or later. 98 99 .. versionadded:: 3.4 100 101 102These symbols define resources whose consumption can be controlled using the 103:func:`setrlimit` and :func:`getrlimit` functions described below. The values of 104these symbols are exactly the constants used by C programs. 105 106The Unix man page for :manpage:`getrlimit(2)` lists the available resources. 107Note that not all systems use the same symbol or same value to denote the same 108resource. This module does not attempt to mask platform differences --- symbols 109not defined for a platform will not be available from this module on that 110platform. 111 112 113.. data:: RLIMIT_CORE 114 115 The maximum size (in bytes) of a core file that the current process can create. 116 This may result in the creation of a partial core file if a larger core would be 117 required to contain the entire process image. 118 119 120.. data:: RLIMIT_CPU 121 122 The maximum amount of processor time (in seconds) that a process can use. If 123 this limit is exceeded, a :const:`SIGXCPU` signal is sent to the process. (See 124 the :mod:`signal` module documentation for information about how to catch this 125 signal and do something useful, e.g. flush open files to disk.) 126 127 128.. data:: RLIMIT_FSIZE 129 130 The maximum size of a file which the process may create. 131 132 133.. data:: RLIMIT_DATA 134 135 The maximum size (in bytes) of the process's heap. 136 137 138.. data:: RLIMIT_STACK 139 140 The maximum size (in bytes) of the call stack for the current process. This only 141 affects the stack of the main thread in a multi-threaded process. 142 143 144.. data:: RLIMIT_RSS 145 146 The maximum resident set size that should be made available to the process. 147 148 149.. data:: RLIMIT_NPROC 150 151 The maximum number of processes the current process may create. 152 153 154.. data:: RLIMIT_NOFILE 155 156 The maximum number of open file descriptors for the current process. 157 158 159.. data:: RLIMIT_OFILE 160 161 The BSD name for :const:`RLIMIT_NOFILE`. 162 163 164.. data:: RLIMIT_MEMLOCK 165 166 The maximum address space which may be locked in memory. 167 168 169.. data:: RLIMIT_VMEM 170 171 The largest area of mapped memory which the process may occupy. 172 173 174.. data:: RLIMIT_AS 175 176 The maximum area (in bytes) of address space which may be taken by the process. 177 178 179.. data:: RLIMIT_MSGQUEUE 180 181 The number of bytes that can be allocated for POSIX message queues. 182 183 .. availability:: Linux 2.6.8 or later. 184 185 .. versionadded:: 3.4 186 187 188.. data:: RLIMIT_NICE 189 190 The ceiling for the process's nice level (calculated as 20 - rlim_cur). 191 192 .. availability:: Linux 2.6.12 or later. 193 194 .. versionadded:: 3.4 195 196 197.. data:: RLIMIT_RTPRIO 198 199 The ceiling of the real-time priority. 200 201 .. availability:: Linux 2.6.12 or later. 202 203 .. versionadded:: 3.4 204 205 206.. data:: RLIMIT_RTTIME 207 208 The time limit (in microseconds) on CPU time that a process can spend 209 under real-time scheduling without making a blocking syscall. 210 211 .. availability:: Linux 2.6.25 or later. 212 213 .. versionadded:: 3.4 214 215 216.. data:: RLIMIT_SIGPENDING 217 218 The number of signals which the process may queue. 219 220 .. availability:: Linux 2.6.8 or later. 221 222 .. versionadded:: 3.4 223 224.. data:: RLIMIT_SBSIZE 225 226 The maximum size (in bytes) of socket buffer usage for this user. 227 This limits the amount of network memory, and hence the amount of mbufs, 228 that this user may hold at any time. 229 230 .. availability:: FreeBSD 9 or later. 231 232 .. versionadded:: 3.4 233 234.. data:: RLIMIT_SWAP 235 236 The maximum size (in bytes) of the swap space that may be reserved or 237 used by all of this user id's processes. 238 This limit is enforced only if bit 1 of the vm.overcommit sysctl is set. 239 Please see :manpage:`tuning(7)` for a complete description of this sysctl. 240 241 .. availability:: FreeBSD 9 or later. 242 243 .. versionadded:: 3.4 244 245.. data:: RLIMIT_NPTS 246 247 The maximum number of pseudo-terminals created by this user id. 248 249 .. availability:: FreeBSD 9 or later. 250 251 .. versionadded:: 3.4 252 253Resource Usage 254-------------- 255 256These functions are used to retrieve resource usage information: 257 258 259.. function:: getrusage(who) 260 261 This function returns an object that describes the resources consumed by either 262 the current process or its children, as specified by the *who* parameter. The 263 *who* parameter should be specified using one of the :const:`RUSAGE_\*` 264 constants described below. 265 266 A simple example:: 267 268 from resource import * 269 import time 270 271 # a non CPU-bound task 272 time.sleep(3) 273 print(getrusage(RUSAGE_SELF)) 274 275 # a CPU-bound task 276 for i in range(10 ** 8): 277 _ = 1 + 1 278 print(getrusage(RUSAGE_SELF)) 279 280 The fields of the return value each describe how a particular system resource 281 has been used, e.g. amount of time spent running is user mode or number of times 282 the process was swapped out of main memory. Some values are dependent on the 283 clock tick internal, e.g. the amount of memory the process is using. 284 285 For backward compatibility, the return value is also accessible as a tuple of 16 286 elements. 287 288 The fields :attr:`ru_utime` and :attr:`ru_stime` of the return value are 289 floating point values representing the amount of time spent executing in user 290 mode and the amount of time spent executing in system mode, respectively. The 291 remaining values are integers. Consult the :manpage:`getrusage(2)` man page for 292 detailed information about these values. A brief summary is presented here: 293 294 +--------+---------------------+---------------------------------------+ 295 | Index | Field | Resource | 296 +========+=====================+=======================================+ 297 | ``0`` | :attr:`ru_utime` | time in user mode (float seconds) | 298 +--------+---------------------+---------------------------------------+ 299 | ``1`` | :attr:`ru_stime` | time in system mode (float seconds) | 300 +--------+---------------------+---------------------------------------+ 301 | ``2`` | :attr:`ru_maxrss` | maximum resident set size | 302 +--------+---------------------+---------------------------------------+ 303 | ``3`` | :attr:`ru_ixrss` | shared memory size | 304 +--------+---------------------+---------------------------------------+ 305 | ``4`` | :attr:`ru_idrss` | unshared memory size | 306 +--------+---------------------+---------------------------------------+ 307 | ``5`` | :attr:`ru_isrss` | unshared stack size | 308 +--------+---------------------+---------------------------------------+ 309 | ``6`` | :attr:`ru_minflt` | page faults not requiring I/O | 310 +--------+---------------------+---------------------------------------+ 311 | ``7`` | :attr:`ru_majflt` | page faults requiring I/O | 312 +--------+---------------------+---------------------------------------+ 313 | ``8`` | :attr:`ru_nswap` | number of swap outs | 314 +--------+---------------------+---------------------------------------+ 315 | ``9`` | :attr:`ru_inblock` | block input operations | 316 +--------+---------------------+---------------------------------------+ 317 | ``10`` | :attr:`ru_oublock` | block output operations | 318 +--------+---------------------+---------------------------------------+ 319 | ``11`` | :attr:`ru_msgsnd` | messages sent | 320 +--------+---------------------+---------------------------------------+ 321 | ``12`` | :attr:`ru_msgrcv` | messages received | 322 +--------+---------------------+---------------------------------------+ 323 | ``13`` | :attr:`ru_nsignals` | signals received | 324 +--------+---------------------+---------------------------------------+ 325 | ``14`` | :attr:`ru_nvcsw` | voluntary context switches | 326 +--------+---------------------+---------------------------------------+ 327 | ``15`` | :attr:`ru_nivcsw` | involuntary context switches | 328 +--------+---------------------+---------------------------------------+ 329 330 This function will raise a :exc:`ValueError` if an invalid *who* parameter is 331 specified. It may also raise :exc:`error` exception in unusual circumstances. 332 333 334.. function:: getpagesize() 335 336 Returns the number of bytes in a system page. (This need not be the same as the 337 hardware page size.) 338 339The following :const:`RUSAGE_\*` symbols are passed to the :func:`getrusage` 340function to specify which processes information should be provided for. 341 342 343.. data:: RUSAGE_SELF 344 345 Pass to :func:`getrusage` to request resources consumed by the calling 346 process, which is the sum of resources used by all threads in the process. 347 348 349.. data:: RUSAGE_CHILDREN 350 351 Pass to :func:`getrusage` to request resources consumed by child processes 352 of the calling process which have been terminated and waited for. 353 354 355.. data:: RUSAGE_BOTH 356 357 Pass to :func:`getrusage` to request resources consumed by both the current 358 process and child processes. May not be available on all systems. 359 360 361.. data:: RUSAGE_THREAD 362 363 Pass to :func:`getrusage` to request resources consumed by the current 364 thread. May not be available on all systems. 365 366 .. versionadded:: 3.2 367