symbian-qemu-0.9.1-12/python-2.6.1/Doc/library/resource.rst
author johnathan.white@2718R8BGH51.accenture.com
Mon, 08 Mar 2010 18:45:03 +0000
changeset 46 b6935a90ca64
parent 1 2fb8b9db1c86
permissions -rw-r--r--
Modify framebuffer and NGA framebuffer to read screen size from board model dtb file. Optimise memory usuage of frame buffer Add example minigui application with hooks to profiler (which writes results to S:\). Modified NGA framebuffer to run its own dfc queue at high priority
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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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.. 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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   ``-1`` can be used to specify the maximum possible upper limit.
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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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   (unless the process has an effective UID of super-user).  Can also raise
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   :exc:`error` if the underlying system call 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.  This only affects the
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   stack of the main thread in a multi-threaded process.
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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.
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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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   123
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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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   191
   +--------+---------------------+-------------------------------+
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   | ``11`` | :attr:`ru_msgsnd`   | messages sent                 |
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   193
   +--------+---------------------+-------------------------------+
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   194
   | ``12`` | :attr:`ru_msgrcv`   | messages received             |
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   195
   +--------+---------------------+-------------------------------+
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   196
   | ``13`` | :attr:`ru_nsignals` | signals received              |
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   197
   +--------+---------------------+-------------------------------+
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   | ``14`` | :attr:`ru_nvcsw`    | voluntary context switches    |
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   199
   +--------+---------------------+-------------------------------+
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   | ``15`` | :attr:`ru_nivcsw`   | involuntary context switches  |
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   +--------+---------------------+-------------------------------+
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   202
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   203
   This function will raise a :exc:`ValueError` if an invalid *who* parameter is
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   204
   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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   210
.. function:: getpagesize()
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   211
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   212
   Returns the number of bytes in a system page. (This need not be the same as the
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   213
   hardware page size.) This function is useful for determining the number of bytes
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   214
   of memory a process is using. The third element of the tuple returned by
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   215
   :func:`getrusage` describes memory usage in pages; multiplying by page size
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   216
   produces number of bytes.
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   217
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   218
The following :const:`RUSAGE_\*` symbols are passed to the :func:`getrusage`
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   219
function to specify which processes information should be provided for.
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   220
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   222
.. data:: RUSAGE_SELF
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   223
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   224
   :const:`RUSAGE_SELF` should be used to request information pertaining only to
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   225
   the process itself.
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   226
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   228
.. data:: RUSAGE_CHILDREN
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   229
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   230
   Pass to :func:`getrusage` to request resource information for child processes of
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   231
   the calling process.
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   232
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   234
.. data:: RUSAGE_BOTH
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   235
2fb8b9db1c86 Initial QEMU (symbian-qemu-0.9.1-12) import
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   236
   Pass to :func:`getrusage` to request resources consumed by both the current
2fb8b9db1c86 Initial QEMU (symbian-qemu-0.9.1-12) import
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   237
   process and child processes.  May not be available on all systems.
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   238