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authorGuido van Rossum <guido@python.org>1996-12-18 18:37:05 (GMT)
committerGuido van Rossum <guido@python.org>1996-12-18 18:37:05 (GMT)
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+\section{Built-in Module \sectcode{resource}}
+
+\bimodindex{resource}
+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.
+
+Resources usage can be limited using the \code{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 process 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 \code{getrlimit} man page. Typical resources
+include:
+
+\begin{description}
+
+\item[RLIMIT_CORE]
+The maximum size (in bytes) of a core file that the current process
+can create.
+
+\item[RLIMIT_CPU]
+The maximum amount of CPU time (in seconds) that a process can use. If
+this limit is exceeded, a \code{SIGXCPU} signal is sent to the
+process. (See the \code{signal} module documentation for information
+about how to catch this signal and do something useful, e.g. flush
+open files to disk.)
+
+\end{description}
+
+\begin{datadesc}{RLIMIT_*}
+ These symbols define resources whose consumption can be controlled
+ using the \code{setrlimit} and \code{getrlimit} functions defined
+ below. The values of these symbols are exactly the constants used
+ by C programs.
+
+ The \UNIX{} man page for \file{getrlimit} lists the available
+ resources. Note that not all systems use the same symbol or same
+ value to denote the same resource.
+\end{datadesc}
+
+\begin{datadesc}{RUSAGE_*}
+ These symbols are passed to the \code{getrusage} function to specify
+ whether usage information is being request for the current process,
+ \code{RUSAGE_SELF} or its child processes \code{RUSAGE_CHILDREN}. On
+ some system, \code{RUSAGE_BOTH} requests information for both.
+\end{datadesc}
+
+\begin{datadesc}{error}
+ The functions described below may raise this error if the underlying
+ system call failures unexpectedly.
+\end{datadesc}
+
+The resource module defines the following functions:
+
+\begin{funcdesc}{getrusage}{who}
+ This function returns a large tuple that describes the resources
+ consumed by either the current process or its children, as specified
+ by the \var{who} parameter. The elements 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.
+
+ The first two elements 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 \code{getrusage} man page
+ for detailed information about these values. A brief summary is
+ presented here:
+
+\begin{tabular}{rl}
+ \emph{offset} & \emph{resource} \\
+ 0 & time in user mode (float) \\
+ 1 & time in system mode (float) \\
+ 2 & maximum resident set size \\
+ 3 & shared memory size \\
+ 4 & unshared memory size \\
+ 5 & unshared stack size \\
+ 6 & page faults not requiring I/O \\
+ 7 & page faults requiring I/O \\
+ 8 & number of swap outs \\
+ 9 & block input operations \\
+ 10 & block output operations \\
+ 11 & messages sent \\
+ 12 & messages received \\
+ 13 & signals received \\
+ 14 & voluntary context switches \\
+ 15 & involuntary context switches \\
+\end{tabular}
+
+ This function will raise a ValueError if an invalid \var{who}
+ parameter is specified. It may also raise a \code{resource.error}
+ exception in unusual circumstances.
+\end{funcdesc}
+
+\begin{funcdesc}{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 \code{getrusage} describes
+ memory usage in pages; multiplying by page size produces number of
+ bytes.
+\end{funcdesc}
+
+\begin{funcdesc}{getrlimit}{resource}
+ Returns a tuple \code{(\var{soft}, \var{hard})} with the current
+ soft and hard limits of \var{resource}. Raises ValueError if
+ an invalid resource is specified, or \code{resource.error} if the
+ underyling system call fails unexpectedly.
+\end{funcdesc}
+
+\begin{funcdesc}{setrlimit}{resource\, limits}
+ Sets new limits of consumption of \var{resource}. The \var{limits}
+ argument must be a tuple \code{(\var{soft}, \var{hard})} of two
+ integers describing the new limits. A value of -1 can be used to
+ specify the maximum possible upper limit.
+
+ 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 (unless the process has an effective UID of
+ super-user). Can also raise a \code{resource.error} if the
+ underyling system call fails.
+\end{funcdesc}