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# 36.13. `resource` — Resource usage information

This module provides basic mechanisms for measuring and controlling system resources utilized by a program.

Symbolic constants are used to specify particular system resources and to request usage information about either the current process or its children.

A single exception is defined for errors:

exception `resource.``error`

  The functions described below may raise this error if the underlying system call failures unexpectedly.

## 36.13.1. Resource Limits

Resources usage can be limited using the `setrlimit()` function described below. Each resource is controlled by a pair of limits: a soft limit and a hard limit. The soft limit is the current limit, and may be lowered or raised by a process over time. The soft limit can never exceed the hard limit. The hard limit can be lowered to any value greater than the soft limit, but not raised. (Only processes with the effective UID of the super-user can raise a hard limit.)

The specific resources that can be limited are system dependent. They are described in the getrlimit(2) man page. The resources listed below are supported when the underlying operating system supports them; resources which cannot be checked or controlled by the operating system are not defined in this module for those platforms.

`resource.``RLIM_INFINITY`

  Constant used to represent the the limit for an unlimited resource.

`resource.``getrlimit`(resource)

  Returns a tuple `(soft, hard)` with the current soft and hard limits of resource. Raises `ValueError` if an invalid resource is specified, or `error` if the underlying system call fails unexpectedly.

`resource.``setrlimit`(resource, limits)

  Sets new limits of consumption of resource. The limits argument must be a tuple `(soft, hard)` of two integers describing the new limits. A value of `RLIM_INFINITY` can be used to request a limit that is unlimited.

  Raises `ValueError` if an invalid resource is specified, if the new soft limit exceeds the hard limit, or if a process tries to raise its hard limit. Specifying a limit of `RLIM_INFINITY` when the hard or system limit for that resource is not unlimited will result in a `ValueError`. A process with the effective UID of super-user can request any valid limit value, including unlimited, but `ValueError` will still be raised if the requested limit exceeds the system imposed limit.

  `setrlimit` may also raise `error` if the underlying system call fails.

These symbols define resources whose consumption can be controlled using the `setrlimit()` and `getrlimit()` functions described below. The values of these symbols are exactly the constants used by C programs.

The Unix man page for getrlimit(2) lists the available resources. Note that not all systems use the same symbol or same value to denote the same resource. This module does not attempt to mask platform differences — symbols not defined for a platform will not be available from this module on that platform.

`resource.``RLIMIT_CORE`

  The maximum size (in bytes) of a core file that the current process can create. This may result in the creation of a partial core file if a larger core would be required to contain the entire process image.

`resource.``RLIMIT_CPU`

  The maximum amount of processor time (in seconds) that a process can use. If this limit is exceeded, a `SIGXCPU` signal is sent to the process. (See the `signal` module documentation for information about how to catch this signal and do something useful, e.g. flush open files to disk.)

`resource.``RLIMIT_FSIZE`

  The maximum size of a file which the process may create. This only affects the stack of the main thread in a multi-threaded process.

`resource.``RLIMIT_DATA`

  The maximum size (in bytes) of the process’s heap.

`resource.``RLIMIT_STACK`

  The maximum size (in bytes) of the call stack for the current process.

`resource.``RLIMIT_RSS`

  The maximum resident set size that should be made available to the process.

`resource.``RLIMIT_NPROC`

  The maximum number of processes the current process may create.

`resource.``RLIMIT_NOFILE`

  The maximum number of open file descriptors for the current process.

`resource.``RLIMIT_OFILE`

  The BSD name for `RLIMIT_NOFILE`.

`resource.``RLIMIT_MEMLOCK`

  The maximum address space which may be locked in memory.

`resource.``RLIMIT_VMEM`

  The largest area of mapped memory which the process may occupy.

`resource.``RLIMIT_AS`

  The maximum area (in bytes) of address space which may be taken by the process.

## 36.13.2. Resource Usage

These functions are used to retrieve resource usage information:

`resource.``getrusage`(who)

  This function returns an object that describes the resources consumed by either the current process or its children, as specified by the who parameter. The who parameter should be specified using one of the `RUSAGE_*` constants described below.

  The fields of the return value each describe how a particular system resource has been used, e.g. amount of time spent running is user mode or number of times the process was swapped out of main memory. Some values are dependent on the clock tick internal, e.g. the amount of memory the process is using.

  For backward compatibility, the return value is also accessible as a tuple of 16 elements.

  The fields `ru_utime` and `ru_stime` of the return value are floating point values representing the amount of time spent executing in user mode and the amount of time spent executing in system mode, respectively. The remaining values are integers. Consult the getrusage(2) man page for detailed information about these values. A brief summary is presented here:

  Index | Field | Resource
  --- | --- | ---
  `0` | `ru_utime` | time in user mode (float)
  `1` | `ru_stime` | time in system mode (float)
  `2` | `ru_maxrss` | maximum resident set size
  `3` | `ru_ixrss` | shared memory size
  `4` | `ru_idrss` | unshared memory size
  `5` | `ru_isrss` | unshared stack size
  `6` | `ru_minflt` | page faults not requiring I/O
  `7` | `ru_majflt` | page faults requiring I/O
  `8` | `ru_nswap` | number of swap outs
  `9` | `ru_inblock` | block input operations
  `10` | `ru_oublock` | block output operations
  `11` | `ru_msgsnd` | messages sent
  `12` | `ru_msgrcv` | messages received
  `13` | `ru_nsignals` | signals received
  `14` | `ru_nvcsw` | voluntary context switches
  `15` | `ru_nivcsw` | involuntary context switches

  This function will raise a `ValueError` if an invalid who parameter is specified. It may also raise `error` exception in unusual circumstances.

  Changed in version 2.3: Added access to values as attributes of the returned object.

`resource.``getpagesize`()

  Returns the number of bytes in a system page. (This need not be the same as the hardware page size.) This function is useful for determining the number of bytes of memory a process is using. The third element of the tuple returned by `getrusage()` describes memory usage in pages; multiplying by page size produces number of bytes.

The following `RUSAGE_*` symbols are passed to the `getrusage()` function to specify which processes information should be provided for.

`resource.``RUSAGE_SELF`

  `RUSAGE_SELF` should be used to request information pertaining only to the process itself.

`resource.``RUSAGE_CHILDREN`

  Pass to `getrusage()` to request resource information for child processes of the calling process.

`resource.``RUSAGE_BOTH`

  Pass to `getrusage()` to request resources consumed by both the current process and child processes. May not be available on all systems.

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