17.4. `signal` — 为异步事件设置处理程序 ¶

This module provides mechanisms to use signal handlers in Python. Some general rules for working with signals and their handlers:

特定信号处理程序一旦设置，仍会安装直到被明确重置 (Python 模拟 BSD 风格接口，不管底层实现)，除了异常处理程序 SIGCHLD 遵循底层实现。
There is no way to “block” signals temporarily from critical sections (since this is not supported by all Unix flavors).
Although Python signal handlers are called asynchronously as far as the Python user is concerned, they can only occur between the “atomic” instructions of the Python interpreter. This means that signals arriving during long calculations implemented purely in C (such as regular expression matches on large bodies of text) may be delayed for an arbitrary amount of time.
When a signal arrives during an I/O operation, it is possible that the I/O operation raises an exception after the signal handler returns. This is dependent on the underlying Unix system’s semantics regarding interrupted system calls.
Because the C signal handler always returns, it makes little sense to catch synchronous errors like SIGFPE or SIGSEGV .
Python installs a small number of signal handlers by default: SIGPIPE 被忽略 (因此，可以将在管道和套接字中写入错误报告成普通 Python 异常) 和 SIGINT 被翻译成 KeyboardInterrupt exception. All of these can be overridden.
Some care must be taken if both signals and threads are used in the same program. The fundamental thing to remember in using signals and threads simultaneously is: always perform signal() operations in the main thread of execution. Any thread can perform an alarm() , getsignal() , pause() , setitimer() or getitimer() ; only the main thread can set a new signal handler, and the main thread will be the only one to receive signals (this is enforced by the Python signal module, even if the underlying thread implementation supports sending signals to individual threads). This means that signals can’t be used as a means of inter-thread communication. Use locks instead.

定义的变量在 signal 模块是：

信号。 SIG_DFL ¶

信号。 SIG_IGN ¶

SIG*

信号。 CTRL_C_EVENT ¶

信号。 CTRL_BREAK_EVENT ¶

信号。 NSIG ¶

信号。 ITIMER_REAL ¶

信号。 ITIMER_VIRTUAL ¶

信号。 ITIMER_PROF ¶

The signal 模块定义了一个异常：

exception 信号。 ItimerError ¶

The signal 模块定义了下列函数：

信号。 alarm ( time ) ¶

信号。 getsignal ( signalnum ) ¶

信号。 pause ( ) ¶

信号。 setitimer ( which , seconds [ , interval ] ) ¶

信号。 getitimer ( which ) ¶

信号。 set_wakeup_fd ( fd ) ¶

信号。 siginterrupt ( signalnum , flag ) ¶

信号。 signal ( signalnum , handler ) ¶

17.4.1. 范例 ¶

Here is a minimal example program. It uses the alarm() function to limit the time spent waiting to open a file; this is useful if the file is for a serial device that may not be turned on, which would normally cause the os.open() to hang indefinitely. The solution is to set a 5-second alarm before opening the file; if the operation takes too long, the alarm signal will be sent, and the handler raises an exception.

import signal, os
def handler(signum, frame):
    print 'Signal handler called with signal', signum
    raise IOError("Couldn't open device!")
# Set the signal handler and a 5-second alarm
signal.signal(signal.SIGALRM, handler)
signal.alarm(5)
# This open() may hang indefinitely
fd = os.open('/dev/ttyS0', os.O_RDWR)
signal.alarm(0)          # Disable the alarm

17.4. signal — 为异步事件设置处理程序 ¶

17.4.1. 范例 ¶

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17.4. `signal` — 为异步事件设置处理程序 ¶