13.13 记录程序执行的时间

You want to place some limits on the memory or CPU use of a program running on

Unix system.

The resource module can be used to perform both tasks. For example, to restrict CPU

time, do the following:

import signal

import resource

import os

print("Time's up!")

raise SystemExit(1)

def set_max_runtime(seconds):

# Install the signal handler and set a resource limit

soft, hard = resource.getrlimit(resource.RLIMIT_CPU)

resource.setrlimit(resource.RLIMIT_CPU, (seconds, hard))

signal.signal(signal.SIGXCPU, time_exceeded)

if __name__ == '__main__':

set_max_runtime(15)

while True:

pass

When this runs, the SIGXCPU signal is generated when the time expires. The program

can then clean up and exit.

To restrict memory use, put a limit on the total address space in use. For example:

def limit_memory(maxsize):

soft, hard = resource.getrlimit(resource.RLIMIT_AS)

resource.setrlimit(resource.RLIMIT_AS, (maxsize, hard))

With a memory limit in place, programs will start generating MemoryError exceptions

when no more memory is available.

In this recipe, the setrlimit() function is used to set a soft and hard limit on a particular

resource. The soft limit is a value upon which the operating system will typically restrict

or notify the process via a signal. The hard limit represents an upper bound on the values

that may be used for the soft limit. Typically, this is controlled by a system-wide pa‐

rameter set by the system administrator. Although the hard limit can be lowered, it can

never be raised by user processes (even if the process lowered itself).

The setrlimit() function can additionally be used to set limits on things such as the

number of child processes, number of open files, and similar system resources. Consult

the documentation for the resource module for further details.

Be aware that this recipe only works on Unix systems, and that it might not work on all

of them. For example, when tested, it works on Linux but not on OS X.