249 lines
9.4 KiB
ReStructuredText
249 lines
9.4 KiB
ReStructuredText
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:mod:`resource` --- Resource usage information
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==============================================
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.. module:: resource
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:platform: Unix
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:synopsis: An interface to provide resource usage information on the current process.
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.. moduleauthor:: Jeremy Hylton <jeremy@alum.mit.edu>
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.. sectionauthor:: Jeremy Hylton <jeremy@alum.mit.edu>
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This module provides basic mechanisms for measuring and controlling system
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resources utilized by a program.
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Symbolic constants are used to specify particular system resources and to
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request usage information about either the current process or its children.
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A single exception is defined for errors:
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.. exception:: error
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The functions described below may raise this error if the underlying system call
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failures unexpectedly.
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Resource Limits
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---------------
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Resources usage can be limited using the :func:`setrlimit` function described
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below. Each resource is controlled by a pair of limits: a soft limit and a hard
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limit. The soft limit is the current limit, and may be lowered or raised by a
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process over time. The soft limit can never exceed the hard limit. The hard
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limit can be lowered to any value greater than the soft limit, but not raised.
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(Only processes with the effective UID of the super-user can raise a hard
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limit.)
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The specific resources that can be limited are system dependent. They are
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described in the :manpage:`getrlimit(2)` man page. The resources listed below
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are supported when the underlying operating system supports them; resources
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which cannot be checked or controlled by the operating system are not defined in
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this module for those platforms.
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.. data:: RLIM_INFINITY
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Constant used to represent the limit for an unlimited resource.
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.. function:: getrlimit(resource)
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Returns a tuple ``(soft, hard)`` with the current soft and hard limits of
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*resource*. Raises :exc:`ValueError` if an invalid resource is specified, or
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:exc:`error` if the underlying system call fails unexpectedly.
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.. function:: setrlimit(resource, limits)
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Sets new limits of consumption of *resource*. The *limits* argument must be a
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tuple ``(soft, hard)`` of two integers describing the new limits. A value of
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:data:`~resource.RLIM_INFINITY` can be used to request a limit that is
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unlimited.
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Raises :exc:`ValueError` if an invalid resource is specified, if the new soft
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limit exceeds the hard limit, or if a process tries to raise its hard limit.
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Specifying a limit of :data:`~resource.RLIM_INFINITY` when the hard or
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system limit for that resource is not unlimited will result in a
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:exc:`ValueError`. A process with the effective UID of super-user can
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request any valid limit value, including unlimited, but :exc:`ValueError`
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will still be raised if the requested limit exceeds the system imposed
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limit.
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``setrlimit`` may also raise :exc:`error` if the underlying system call
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fails.
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These symbols define resources whose consumption can be controlled using the
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:func:`setrlimit` and :func:`getrlimit` functions described below. The values of
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these symbols are exactly the constants used by C programs.
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The Unix man page for :manpage:`getrlimit(2)` lists the available resources.
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Note that not all systems use the same symbol or same value to denote the same
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resource. This module does not attempt to mask platform differences --- symbols
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not defined for a platform will not be available from this module on that
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platform.
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.. data:: RLIMIT_CORE
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The maximum size (in bytes) of a core file that the current process can create.
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This may result in the creation of a partial core file if a larger core would be
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required to contain the entire process image.
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.. data:: RLIMIT_CPU
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The maximum amount of processor time (in seconds) that a process can use. If
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this limit is exceeded, a :const:`SIGXCPU` signal is sent to the process. (See
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the :mod:`signal` module documentation for information about how to catch this
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signal and do something useful, e.g. flush open files to disk.)
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.. data:: RLIMIT_FSIZE
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The maximum size of a file which the process may create.
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.. data:: RLIMIT_DATA
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The maximum size (in bytes) of the process's heap.
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.. data:: RLIMIT_STACK
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The maximum size (in bytes) of the call stack for the current process. This only
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affects the stack of the main thread in a multi-threaded process.
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.. data:: RLIMIT_RSS
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The maximum resident set size that should be made available to the process.
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.. data:: RLIMIT_NPROC
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The maximum number of processes the current process may create.
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.. data:: RLIMIT_NOFILE
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The maximum number of open file descriptors for the current process.
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.. data:: RLIMIT_OFILE
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The BSD name for :const:`RLIMIT_NOFILE`.
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.. data:: RLIMIT_MEMLOCK
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The maximum address space which may be locked in memory.
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.. data:: RLIMIT_VMEM
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The largest area of mapped memory which the process may occupy.
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.. data:: RLIMIT_AS
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The maximum area (in bytes) of address space which may be taken by the process.
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Resource Usage
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--------------
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These functions are used to retrieve resource usage information:
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.. function:: getrusage(who)
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This function returns an object that describes the resources consumed by either
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the current process or its children, as specified by the *who* parameter. The
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*who* parameter should be specified using one of the :const:`RUSAGE_\*`
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constants described below.
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The fields of the return value each describe how a particular system resource
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has been used, e.g. amount of time spent running is user mode or number of times
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the process was swapped out of main memory. Some values are dependent on the
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clock tick internal, e.g. the amount of memory the process is using.
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For backward compatibility, the return value is also accessible as a tuple of 16
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elements.
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The fields :attr:`ru_utime` and :attr:`ru_stime` of the return value are
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floating point values representing the amount of time spent executing in user
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mode and the amount of time spent executing in system mode, respectively. The
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remaining values are integers. Consult the :manpage:`getrusage(2)` man page for
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detailed information about these values. A brief summary is presented here:
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+--------+---------------------+-------------------------------+
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| Index | Field | Resource |
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+========+=====================+===============================+
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| ``0`` | :attr:`ru_utime` | time in user mode (float) |
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+--------+---------------------+-------------------------------+
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| ``1`` | :attr:`ru_stime` | time in system mode (float) |
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+--------+---------------------+-------------------------------+
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| ``2`` | :attr:`ru_maxrss` | maximum resident set size |
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+--------+---------------------+-------------------------------+
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| ``3`` | :attr:`ru_ixrss` | shared memory size |
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+--------+---------------------+-------------------------------+
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| ``4`` | :attr:`ru_idrss` | unshared memory size |
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+--------+---------------------+-------------------------------+
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| ``5`` | :attr:`ru_isrss` | unshared stack size |
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+--------+---------------------+-------------------------------+
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| ``6`` | :attr:`ru_minflt` | page faults not requiring I/O |
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+--------+---------------------+-------------------------------+
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| ``7`` | :attr:`ru_majflt` | page faults requiring I/O |
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+--------+---------------------+-------------------------------+
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| ``8`` | :attr:`ru_nswap` | number of swap outs |
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+--------+---------------------+-------------------------------+
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| ``9`` | :attr:`ru_inblock` | block input operations |
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+--------+---------------------+-------------------------------+
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| ``10`` | :attr:`ru_oublock` | block output operations |
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+--------+---------------------+-------------------------------+
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| ``11`` | :attr:`ru_msgsnd` | messages sent |
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+--------+---------------------+-------------------------------+
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| ``12`` | :attr:`ru_msgrcv` | messages received |
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+--------+---------------------+-------------------------------+
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| ``13`` | :attr:`ru_nsignals` | signals received |
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+--------+---------------------+-------------------------------+
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| ``14`` | :attr:`ru_nvcsw` | voluntary context switches |
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+--------+---------------------+-------------------------------+
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| ``15`` | :attr:`ru_nivcsw` | involuntary context switches |
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+--------+---------------------+-------------------------------+
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This function will raise a :exc:`ValueError` if an invalid *who* parameter is
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specified. It may also raise :exc:`error` exception in unusual circumstances.
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.. versionchanged:: 2.3
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Added access to values as attributes of the returned object.
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.. function:: getpagesize()
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Returns the number of bytes in a system page. (This need not be the same as the
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hardware page size.)
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The following :const:`RUSAGE_\*` symbols are passed to the :func:`getrusage`
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function to specify which processes information should be provided for.
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.. data:: RUSAGE_SELF
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:const:`RUSAGE_SELF` should be used to request information pertaining only to
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the process itself.
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.. data:: RUSAGE_CHILDREN
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Pass to :func:`getrusage` to request resource information for child processes of
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the calling process.
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.. data:: RUSAGE_BOTH
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Pass to :func:`getrusage` to request resources consumed by both the current
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process and child processes. May not be available on all systems.
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