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:
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.
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 -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 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.
These functions are used to retrieve resource usage information:
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:
|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|
|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.
The following RUSAGE_* symbols are passed to the getrusage() function to specify which processes information should be provided for.