201 lines
7.4 KiB
TeX
201 lines
7.4 KiB
TeX
\section{Built-in Module \module{resource}}
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\label{module-resource}
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\bimodindex{resource}
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This module provides basic mechanisms for measuring and controlling
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system resources utilized by a program.
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Symbolic constants are used to specify particular system resources and
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to request usage information about either the current process or its
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children.
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A single exception is defined for errors:
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\begin{excdesc}{error}
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The functions described below may raise this error if the underlying
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system call failures unexpectedly.
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\end{excdesc}
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\subsection{Resource Limits}
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Resources usage can be limited using the \function{setrlimit()} function
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described below. Each resource is controlled by a pair of limits: a
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soft limit and a hard limit. The soft limit is the current limit, and
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may be lowered or raised by a process over time. The soft limit can
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never exceed the hard limit. The hard limit can be lowered to any
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value greater than the soft limit, but not raised. (Only processes with
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the effective UID of the super-user can raise a hard limit.)
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The specific resources that can be limited are system dependent. They
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are described in the \manpage{getrlimit}{2} man page. The resources
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listed below are supported when the underlying operating system
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supports them; resources which cannot be checked or controlled by the
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operating system are not defined in this module for those platforms.
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\begin{funcdesc}{getrlimit}{resource}
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Returns a tuple \code{(\var{soft}, \var{hard})} with the current
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soft and hard limits of \var{resource}. Raises \exception{ValueError} if
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an invalid resource is specified, or \exception{error} if the
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underyling system call fails unexpectedly.
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\end{funcdesc}
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\begin{funcdesc}{setrlimit}{resource, limits}
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Sets new limits of consumption of \var{resource}. The \var{limits}
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argument must be a tuple \code{(\var{soft}, \var{hard})} of two
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integers describing the new limits. A value of \code{-1} can be used to
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specify the maximum possible upper limit.
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Raises \exception{ValueError} if an invalid resource is specified,
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if the new soft limit exceeds the hard limit, or if a process tries
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to raise its hard limit (unless the process has an effective UID of
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super-user). Can also raise \exception{error} if the underyling
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system call fails.
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\end{funcdesc}
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These symbols define resources whose consumption can be controlled
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using the \function{setrlimit()} and \function{getrlimit()} functions
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described below. The values of these symbols are exactly the constants
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used by \C{} programs.
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The \UNIX{} man page for \manpage{getrlimit}{2} lists the available
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resources. Note that not all systems use the same symbol or same
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value to denote the same resource.
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\begin{datadesc}{RLIMIT_CORE}
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The maximum size (in bytes) of a core file that the current process
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can create. This may result in the creation of a partial core file
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if a larger core would be required to contain the entire process
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image.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_CPU}
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The maximum amount of CPU time (in seconds) that a process can
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use. If this limit is exceeded, a \constant{SIGXCPU} signal is sent to
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the process. (See the \module{signal} module documentation for
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information about how to catch this signal and do something useful,
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e.g. flush open files to disk.)
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\end{datadesc}
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\begin{datadesc}{RLIMIT_FSIZE}
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The maximum size of a file which the process may create. This only
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affects the stack of the main thread in a multi-threaded process.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_DATA}
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The maximum size (in bytes) of the process's heap.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_STACK}
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The maximum size (in bytes) of the call stack for the current
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process.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_RSS}
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The maximum resident set size that should be made available to the
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process.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_NPROC}
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The maximum number of processes the current process may create.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_NOFILE}
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The maximum number of open file descriptors for the current
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process.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_OFILE}
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The BSD name for \constant{RLIMIT_NOFILE}.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_MEMLOC}
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The maximm address space which may be locked in memory.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_VMEM}
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The largest area of mapped memory which the process may occupy.
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\end{datadesc}
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\begin{datadesc}{RLIMIT_AS}
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The maximum area (in bytes) of address space which may be taken by
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the process.
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\end{datadesc}
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\subsection{Resource Usage}
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These functiona are used to retrieve resource usage information:
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\begin{funcdesc}{getrusage}{who}
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This function returns a large tuple that describes the resources
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consumed by either the current process or its children, as specified
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by the \var{who} parameter. The \var{who} parameter should be
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specified using one of the \code{RUSAGE_*} constants described
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below.
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The elements of the return value each
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describe how a particular system resource has been used, e.g. amount
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of time spent running is user mode or number of times the process was
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swapped out of main memory. Some values are dependent on the clock
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tick internal, e.g. the amount of memory the process is using.
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The first two elements of the return value are floating point values
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representing the amount of time spent executing in user mode and the
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amount of time spent executing in system mode, respectively. The
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remaining values are integers. Consult the \manpage{getrusage}{2}
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man page for detailed information about these values. A brief
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summary is presented here:
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\begin{tableii}{r|l}{code}{Offset}{Resource}
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\lineii{0}{time in user mode (float)}
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\lineii{1}{time in system mode (float)}
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\lineii{2}{maximum resident set size}
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\lineii{3}{shared memory size}
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\lineii{4}{unshared memory size}
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\lineii{5}{unshared stack size}
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\lineii{6}{page faults not requiring I/O}
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\lineii{7}{page faults requiring I/O}
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\lineii{8}{number of swap outs}
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\lineii{9}{block input operations}
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\lineii{10}{block output operations}
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\lineii{11}{messages sent}
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\lineii{12}{messages received}
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\lineii{13}{signals received}
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\lineii{14}{voluntary context switches}
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\lineii{15}{involuntary context switches}
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\end{tableii}
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This function will raise a \exception{ValueError} if an invalid
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\var{who} parameter is specified. It may also raise
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\exception{error} exception in unusual circumstances.
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\end{funcdesc}
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\begin{funcdesc}{getpagesize}{}
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Returns the number of bytes in a system page. (This need not be the
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same as the hardware page size.) This function is useful for
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determining the number of bytes of memory a process is using. The
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third element of the tuple returned by \function{getrusage()} describes
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memory usage in pages; multiplying by page size produces number of
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bytes.
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\end{funcdesc}
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The following \code{RUSAGE_*} symbols are passed to the
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\function{getrusage()} function to specify which processes information
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should be provided for.
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\begin{datadesc}{RUSAGE_SELF}
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\constant{RUSAGE_SELF} should be used to
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request information pertaining only to the process itself.
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\end{datadesc}
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\begin{datadesc}{RUSAGE_CHILDREN}
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Pass to \function{getrusage()} to request resource information for
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child processes of the calling process.
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\end{datadesc}
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\begin{datadesc}{RUSAGE_BOTH}
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Pass to \function{getrusage()} to request resources consumed by both
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the current process and child processes. May not be available on all
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systems.
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\end{datadesc}
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