signal
selectors — 高级 I/O 复用
selectors
源代码： Lib/signal.py
此模块提供在 Python 中使用信号处理程序的机制。
The signal.signal() 函数允许定义要执行的自定义处理程序，当收到信号时。有安装少量默认处理程序： 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 异常若父级进程没有改变它。
signal.signal()
SIGPIPE
SIGINT
KeyboardInterrupt
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。
SIGCHLD
在 WebAssembly 平台 wasm32-emscripten and wasm32-wasi ，信号是模拟的因此行为不同。有几个函数和信号不可用于这些平台。
wasm32-emscripten
wasm32-wasi
Python 信号处理程序在低级 C 信号处理程序内，不会获得执行。相反，低级信号处理程序设置标志告诉 虚拟机 稍后要执行相应 Python 信号处理程序 (例如下一 bytecode 指令)。这有后果：
它使捕获同步错误变得意义不大像 SIGFPE or SIGSEGV 是由 C 代码中的无效操作造成的。Python 将从信号处理程序返回到 C 代码，很可能再次引发相同信号，导致 Python 被明显挂起。从 Python 3.3 起，可以使用 faulthandler 模块报告同步错误。
SIGFPE
SIGSEGV
faulthandler
以纯 C 实现的长时间运行的计算 (例如：正则表达式匹配大量文本) 可以在任意时间内不间断运行，不管收到什么信号。将调用 Python 信号处理程序当计算完成时。
若处理程序引发异常，它会在主线程中被 "无中生有" 引发。见 下文注意事项 了解讨论。
Python 信号处理程序始终在主解释器的主 Python 线程中执行，即使信号是在另一线程中收到的。这意味着不可以把信号，用作线程间的通信手段。可以使用同步原语来自 threading 模块代替。
threading
此外，只允许主解释器的主线程设置新的信号处理程序。
3.5 版改变： 信号 (SIG*)，处理程序 ( SIG_DFL , SIG_IGN ) and sigmask ( SIG_BLOCK , SIG_UNBLOCK , SIG_SETMASK ) 下面列出的相关常数被转换成 enums ( Signals , Handlers and Sigmasks 分别)。 getsignal() , pthread_sigmask() , sigpending() and sigwait() 函数返回人类可读的 enums as Signals 对象。
SIG_DFL
SIG_IGN
SIG_BLOCK
SIG_UNBLOCK
SIG_SETMASK
enums
Signals
Handlers
Sigmasks
getsignal()
pthread_sigmask()
sigpending()
sigwait()
signal 模块定义了 3 个枚举：
enum.IntEnum collection of SIG* constants and the CTRL_* constants.
enum.IntEnum
Added in version 3.5.
enum.IntEnum 收集常量 SIG_DFL and SIG_IGN .
enum.IntEnum 收集常量 SIG_BLOCK , SIG_UNBLOCK and SIG_SETMASK .
可用性 ：Unix。
见手册页 sigprocmask(2) and pthread_sigmask(3) 了解进一步信息。
定义的变量在 signal 模块是：
This is one of two standard signal handling options; it will simply perform the default function for the signal. For example, on most systems the default action for SIGQUIT is to dump core and exit, while the default action for SIGCHLD is to simply ignore it.
SIGQUIT
这是另一标准信号处理程序，将简单忽略给定信号。
中止信号来自 abort(3) .
计时器信号来自 alarm(2) .
中断来自键盘 (CTRL + BREAK)。
可用性 ：Windows。
总线错误 (坏的内存访问)。
子进程已停止 (或已终止)。
别名 SIGCHLD .
可用性 : not macOS.
继续若进程目前已停止
浮点异常。例如，除以 0。
另请参阅
ZeroDivisionError 被引发当除法 (或模) 运算的第 2 自变量为 0。
ZeroDivisionError
在控制终端检测到挂起 (或控制进程死亡)。
非法指令。
中断来自键盘 (CTRL + C)。
默认动作是引发 KeyboardInterrupt .
杀除信号。
它无法被捕获、阻塞或忽略。
已断开的管道：向没有读取器的管道写入。
默认动作是忽略信号。
分段故障：无效的内存引用。
协处理器中的堆栈故障。Linux 内核不引发此信号：只可以在用户空间中引发它。
可用性 ：Linux。
在信号可用的体系结构中。见手册页 signal(7) 了解进一步信息。
Added in version 3.11.
终止信号。
用户定义信号 1。
用户定义信号 2。
窗口重置大小信号。
All the signal numbers are defined symbolically. For example, the hangup signal is defined as signal.SIGHUP ; the variable names are identical to the names used in C programs, as found in <signal.h> . The Unix man page for ‘ signal() ’ lists the existing signals (on some systems this is signal(2) , on others the list is in signal(7) ). Note that not all systems define the same set of signal names; only those names defined by the system are defined by this module.
signal.SIGHUP
<signal.h>
signal()
信号对应 Ctrl + C 击键事件。此信号只可用于 os.kill() .
os.kill()
Added in version 3.2.
信号对应 Ctrl + Break 击键事件。此信号只可用于 os.kill() .
One more than the number of the highest signal number. Use valid_signals() to get valid signal numbers.
valid_signals()
Decrements interval timer in real time, and delivers SIGALRM upon expiration.
SIGALRM
Decrements interval timer only when the process is executing, and delivers SIGVTALRM upon expiration.
Decrements interval timer both when the process executes and when the system is executing on behalf of the process. Coupled with ITIMER_VIRTUAL, this timer is usually used to profile the time spent by the application in user and kernel space. SIGPROF is delivered upon expiration.
A possible value for the how 参数用于 pthread_sigmask() indicating that signals are to be blocked.
Added in version 3.3.
A possible value for the how 参数用于 pthread_sigmask() indicating that signals are to be unblocked.
A possible value for the how 参数用于 pthread_sigmask() indicating that the signal mask is to be replaced.
The signal 模块定义了一个异常：
Raised to signal an error from the underlying setitimer() or getitimer() implementation. Expect this error if an invalid interval timer or a negative time is passed to setitimer() . This error is a subtype of OSError .
setitimer()
getitimer()
OSError
Added in version 3.3: This error used to be a subtype of IOError ，现在是别名化的 OSError .
IOError
The signal 模块定义了下列函数：
若 time is non-zero, this function requests that a SIGALRM signal be sent to the process in time seconds. Any previously scheduled alarm is canceled (only one alarm can be scheduled at any time). The returned value is then the number of seconds before any previously set alarm was to have been delivered. If time is zero, no alarm is scheduled, and any scheduled alarm is canceled. If the return value is zero, no alarm is currently scheduled.
见手册页 alarm(2) 了解进一步信息。
Return the current signal handler for the signal signalnum . The returned value may be a callable Python object, or one of the special values signal.SIG_IGN , signal.SIG_DFL or None . Here, signal.SIG_IGN means that the signal was previously ignored, signal.SIG_DFL means that the default way of handling the signal was previously in use, and None means that the previous signal handler was not installed from Python.
signal.SIG_IGN
signal.SIG_DFL
None
Returns the description of signal signalnum , such as “Interrupt” for SIGINT 。返回 None if signalnum has no description. Raises ValueError if signalnum 无效。
ValueError
Added in version 3.8.
Return the set of valid signal numbers on this platform. This can be less than range(1, NSIG) if some signals are reserved by the system for internal use.
range(1, NSIG)
Cause the process to sleep until a signal is received; the appropriate handler will then be called. Returns nothing.
见手册页 signal(2) 了解进一步信息。
另请参阅 sigwait() , sigwaitinfo() , sigtimedwait() and sigpending() .
sigwaitinfo()
sigtimedwait()
把信号发送给调用进程。什么都不返回。
发送信号 sig to the process referred to by file descriptor pidfd . Python does not currently support the siginfo parameter; it must be None 。 flags 自变量是为未来扩展而提供的；目前没有定义标志值。
见 pidfd_send_signal(2) 手册页了解更多信息。
可用性 : Linux >= 5.1
Added in version 3.9.
发送信号 signalnum to the thread thread_id , another thread in the same process as the caller. The target thread can be executing any code (Python or not). However, if the target thread is executing the Python interpreter, the Python signal handlers will be executed by the main thread of the main interpreter . Therefore, the only point of sending a signal to a particular Python thread would be to force a running system call to fail with InterruptedError .
InterruptedError
使用 threading.get_ident() 或 ident attribute of threading.Thread objects to get a suitable value for thread_id .
threading.get_ident()
ident
threading.Thread
若 signalnum is 0, then no signal is sent, but error checking is still performed; this can be used to check if the target thread is still running.
引发 审计事件 signal.pthread_kill 采用自变量 thread_id , signalnum .
signal.pthread_kill
thread_id
signalnum
见手册页 pthread_kill(3) 了解进一步信息。
另请参阅 os.kill() .
Fetch and/or change the signal mask of the calling thread. The signal mask is the set of signals whose delivery is currently blocked for the caller. Return the old signal mask as a set of signals.
The behavior of the call is dependent on the value of how , as follows.
SIG_BLOCK : The set of blocked signals is the union of the current set and the mask 自变量。
SIG_UNBLOCK : The signals in mask are removed from the current set of blocked signals. It is permissible to attempt to unblock a signal which is not blocked.
SIG_SETMASK : The set of blocked signals is set to the mask 自变量。
mask is a set of signal numbers (e.g. { signal.SIGINT , signal.SIGTERM }). Use valid_signals() for a full mask including all signals.
signal.SIGINT
signal.SIGTERM
例如， signal.pthread_sigmask(signal.SIG_BLOCK, []) reads the signal mask of the calling thread.
signal.pthread_sigmask(signal.SIG_BLOCK, [])
SIGKILL and SIGSTOP cannot be blocked.
SIGKILL
SIGSTOP
另请参阅 pause() , sigpending() and sigwait() .
pause()
Sets given interval timer (one of signal.ITIMER_REAL , signal.ITIMER_VIRTUAL or signal.ITIMER_PROF ) specified by which to fire after seconds (float is accepted, different from alarm() ) and after that every interval seconds (if interval is non-zero). The interval timer specified by which can be cleared by setting seconds to zero.
signal.ITIMER_REAL
signal.ITIMER_VIRTUAL
signal.ITIMER_PROF
alarm()
When an interval timer fires, a signal is sent to the process. The signal sent is dependent on the timer being used; signal.ITIMER_REAL will deliver SIGALRM , signal.ITIMER_VIRTUAL sends SIGVTALRM ，和 signal.ITIMER_PROF will deliver SIGPROF .
SIGVTALRM
SIGPROF
The old values are returned as a tuple: (delay, interval).
Attempting to pass an invalid interval timer will cause an ItimerError .
ItimerError
Returns current value of a given interval timer specified by which .
Set the wakeup file descriptor to fd . When a signal is received, the signal number is written as a single byte into the fd. This can be used by a library to wakeup a poll or select call, allowing the signal to be fully processed.
The old wakeup fd is returned (or -1 if file descriptor wakeup was not enabled). If fd is -1, file descriptor wakeup is disabled. If not -1, fd must be non-blocking. It is up to the library to remove any bytes from fd before calling poll or select again.
当启用线程时，此函数才可以被调用从 主解释器的主线程 ; attempting to call it from other threads will cause a ValueError exception to be raised.
There are two common ways to use this function. In both approaches, you use the fd to wake up when a signal arrives, but then they differ in how they determine which signal or signals have arrived.
In the first approach, we read the data out of the fd’s buffer, and the byte values give you the signal numbers. This is simple, but in rare cases it can run into a problem: generally the fd will have a limited amount of buffer space, and if too many signals arrive too quickly, then the buffer may become full, and some signals may be lost. If you use this approach, then you should set warn_on_full_buffer=True , which will at least cause a warning to be printed to stderr when signals are lost.
warn_on_full_buffer=True
In the second approach, we use the wakeup fd only for wakeups, and ignore the actual byte values. In this case, all we care about is whether the fd’s buffer is empty or non-empty; a full buffer doesn’t indicate a problem at all. If you use this approach, then you should set warn_on_full_buffer=False , so that your users are not confused by spurious warning messages.
warn_on_full_buffer=False
3.5 版改变： 在 Windows，函数现在还支持套接字句柄。
3.7 版改变： 添加 warn_on_full_buffer 参数。
warn_on_full_buffer
更改系统调用的重启行为：若 flag is False , system calls will be restarted when interrupted by signal signalnum , otherwise system calls will be interrupted. Returns nothing.
False
见手册页 siginterrupt(3) 了解进一步信息。
Note that installing a signal handler with signal() will reset the restart behaviour to interruptible by implicitly calling siginterrupt() with a true flag value for the given signal.
siginterrupt()
设置处理程序为信号 signalnum 到函数 handler . handler 可以是接受 2 自变量的可调用 Python 对象 (见下文)，或者是某一特殊值 signal.SIG_IGN or signal.SIG_DFL 。将返回先前的信号处理程序 (见描述为 getsignal() 上文)。（见 Unix 手册页 signal(2) 了解进一步信息。)
The handler is called with two arguments: the signal number and the current stack frame ( None or a frame object; for a description of frame objects, see the description in the type hierarchy or see the attribute descriptions in the inspect 模块)。
inspect
在 Windows， signal() 才可以被调用采用 SIGABRT , SIGFPE , SIGILL , SIGINT , SIGSEGV , SIGTERM ，或 SIGBREAK 。 ValueError will be raised in any other case. Note that not all systems define the same set of signal names; an AttributeError will be raised if a signal name is not defined as SIG* module level constant.
SIGABRT
SIGILL
SIGTERM
SIGBREAK
AttributeError
SIG*
Examine the set of signals that are pending for delivery to the calling thread (i.e., the signals which have been raised while blocked). Return the set of the pending signals.
见手册页 sigpending(2) 了解进一步信息。
另请参阅 pause() , pthread_sigmask() and sigwait() .
Suspend execution of the calling thread until the delivery of one of the signals specified in the signal set sigset . The function accepts the signal (removes it from the pending list of signals), and returns the signal number.
见手册页 sigwait(3) 了解进一步信息。
另请参阅 pause() , pthread_sigmask() , sigpending() , sigwaitinfo() and sigtimedwait() .
Suspend execution of the calling thread until the delivery of one of the signals specified in the signal set sigset . The function accepts the signal and removes it from the pending list of signals. If one of the signals in sigset is already pending for the calling thread, the function will return immediately with information about that signal. The signal handler is not called for the delivered signal. The function raises an InterruptedError if it is interrupted by a signal that is not in sigset .
The return value is an object representing the data contained in the siginfo_t structure, namely: si_signo , si_code , si_errno , si_pid , si_uid , si_status , si_band .
siginfo_t
si_signo
si_code
si_errno
si_pid
si_uid
si_status
si_band
见手册页 sigwaitinfo(2) 了解进一步信息。
另请参阅 pause() , sigwait() and sigtimedwait() .
3.5 版改变： The function is now retried if interrupted by a signal not in sigset and the signal handler does not raise an exception (see PEP 475 了解基本原理)。
像 sigwaitinfo() , but takes an additional timeout argument specifying a timeout. If timeout is specified as 0 , a poll is performed. Returns None if a timeout occurs.
0
见手册页 sigtimedwait(2) 了解进一步信息。
另请参阅 pause() , sigwait() and sigwaitinfo() .
3.5 版改变： The function is now retried with the recomputed timeout if interrupted by a signal not in sigset and the signal handler does not raise an exception (see PEP 475 了解基本原理)。
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.
os.open()
import signal, os def handler(signum, frame): signame = signal.Signals(signum).name print(f'Signal handler called with signal {signame} ({signum})') raise OSError("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
Piping output of your program to tools like head(1) will cause a SIGPIPE signal to be sent to your process when the receiver of its standard output closes early. This results in an exception like BrokenPipeError: [Errno 32] Broken pipe . To handle this case, wrap your entry point to catch this exception as follows:
BrokenPipeError: [Errno 32] Broken pipe
import os import sys def main(): try: # simulate large output (your code replaces this loop) for x in range(10000): print("y") # flush output here to force SIGPIPE to be triggered # while inside this try block. sys.stdout.flush() except BrokenPipeError: # Python flushes standard streams on exit; redirect remaining output # to devnull to avoid another BrokenPipeError at shutdown devnull = os.open(os.devnull, os.O_WRONLY) os.dup2(devnull, sys.stdout.fileno()) sys.exit(1) # Python exits with error code 1 on EPIPE if __name__ == '__main__': main()
Do not set SIGPIPE ’s disposition to SIG_DFL in order to avoid BrokenPipeError . Doing that would cause your program to exit unexpectedly whenever any socket connection is interrupted while your program is still writing to it.
BrokenPipeError
If a signal handler raises an exception, the exception will be propagated to the main thread and may be raised after any bytecode instruction. Most notably, a KeyboardInterrupt may appear at any point during execution. Most Python code, including the standard library, cannot be made robust against this, and so a KeyboardInterrupt (or any other exception resulting from a signal handler) may on rare occasions put the program in an unexpected state.
To illustrate this issue, consider the following code:
class SpamContext: def __init__(self): self.lock = threading.Lock() def __enter__(self): # If KeyboardInterrupt occurs here, everything is fine self.lock.acquire() # If KeyboardInterrupt occurs here, __exit__ will not be called ... # KeyboardInterrupt could occur just before the function returns def __exit__(self, exc_type, exc_val, exc_tb): ... self.lock.release()
For many programs, especially those that merely want to exit on KeyboardInterrupt , this is not a problem, but applications that are complex or require high reliability should avoid raising exceptions from signal handlers. They should also avoid catching KeyboardInterrupt as a means of gracefully shutting down. Instead, they should install their own SIGINT handler. Below is an example of an HTTP server that avoids KeyboardInterrupt :
import signal import socket from selectors import DefaultSelector, EVENT_READ from http.server import HTTPServer, SimpleHTTPRequestHandler interrupt_read, interrupt_write = socket.socketpair() def handler(signum, frame): print('Signal handler called with signal', signum) interrupt_write.send(b'\0') signal.signal(signal.SIGINT, handler) def serve_forever(httpd): sel = DefaultSelector() sel.register(interrupt_read, EVENT_READ) sel.register(httpd, EVENT_READ) while True: for key, _ in sel.select(): if key.fileobj == interrupt_read: interrupt_read.recv(1) return if key.fileobj == httpd: httpd.handle_request() print("Serving on port 8000") httpd = HTTPServer(('', 8000), SimpleHTTPRequestHandler) serve_forever(httpd) print("Shutdown...")
mmap — 内存映射文件支持
mmap
键入搜索术语或模块、类、函数名称。