signal
— 为异步事件设置处理程序
¶
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。
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。
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：
SIGFPE
or
SIGSEGV
that are caused by an invalid operation in C code. Python
will return from the signal handler to the C code, which is likely to raise
the same signal again, causing Python to apparently hang. From Python 3.3
onwards, you can use the
faulthandler
module to report on synchronous
errors.
Python signal handlers are always executed in the main Python thread, even if the signal was received in another thread. This means that signals can’t be used as a means of inter-thread communication. You can use the synchronization primitives from the
threading
模块代替。
Besides, only the main thread is allowed to set a new signal handler.
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
.
getsignal()
,
pthread_sigmask()
,
sigpending()
and
sigwait()
函数返回人类可读的
enums
.
定义的变量在
signal
模块是：
信号。
SIG_DFL
¶
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.
信号。
SIG_IGN
¶
这是另一标准信号处理程序，将简单忽略给定信号。
SIG*
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.
信号。
NSIG
¶
One more than the number of the highest signal number.
信号。
ITIMER_REAL
¶
Decrements interval timer in real time, and delivers
SIGALRM
upon expiration.
信号。
ITIMER_VIRTUAL
¶
Decrements interval timer only when the process is executing, and delivers SIGVTALRM upon expiration.
信号。
ITIMER_PROF
¶
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.
信号。
SIG_BLOCK
¶
A possible value for the
how
参数用于
pthread_sigmask()
indicating that signals are to be blocked.
3.3 版新增。
信号。
SIG_UNBLOCK
¶
A possible value for the
how
参数用于
pthread_sigmask()
indicating that signals are to be unblocked.
3.3 版新增。
信号。
SIG_SETMASK
¶
A possible value for the
how
参数用于
pthread_sigmask()
indicating that the signal mask is to be replaced.
3.3 版新增。
The
signal
模块定义了一个异常：
信号。
ItimerError
¶
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
.
3.3 版新增：
This error used to be a subtype of
IOError
，现在是别名化的
OSError
.
The
signal
模块定义了下列函数：
信号。
alarm
(
time
)
¶
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. (See the Unix man page
alarm(2)
.) Availability: Unix.
信号。
getsignal
(
signalnum
)
¶
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.
信号。
pause
(
)
¶
Cause the process to sleep until a signal is received; the appropriate handler will then be called. Returns nothing. Not on Windows. (See the Unix man page signal(2) )。
另请参阅
sigwait()
,
sigwaitinfo()
,
sigtimedwait()
and
sigpending()
.
信号。
pthread_kill
(
thread_id
,
signalnum
)
¶
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
. 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
.
使用
threading.get_ident()
或
ident
attribute of
threading.Thread
objects to get a suitable value for
thread_id
.
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.
可用性：Unix (见手册页 pthread_kill(3) 了解进一步信息)。
另请参阅
os.kill()
.
3.3 版新增。
信号。
pthread_sigmask
(
how
,
mask
)
¶
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
range(1, signal.NSIG)
for a full mask including all signals.
例如，
signal.pthread_sigmask(signal.SIG_BLOCK, [])
reads the signal mask of the calling thread.
Availability: Unix. See the man page sigprocmask(3) and pthread_sigmask(3) 了解进一步信息。
另请参阅
pause()
,
sigpending()
and
sigwait()
.
3.3 版新增。
信号。
setitimer
(
which
,
seconds
[
,
interval
]
)
¶
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. The interval timer specified by
which
can be cleared by setting seconds to zero.
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
.
The old values are returned as a tuple: (delay, interval).
Attempting to pass an invalid interval timer will cause an
ItimerError
. Availability: Unix.
信号。
getitimer
(
which
)
¶
Returns current value of a given interval timer specified by which . Availability: Unix.
信号。
set_wakeup_fd
(
fd
)
¶
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.
Use for example
struct.unpack('%uB' % len(data), data)
to decode the signal numbers list.
When threads are enabled, this function can only be called from the main thread; attempting to call it from other threads will cause a
ValueError
exception to be raised.
3.5 版改变： 在 Windows，函数现在还支持套接字句柄。
信号。
siginterrupt
(
signalnum
,
flag
)
¶
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. Availability: Unix (see the man page
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.
信号。
signal
(
signalnum
,
handler
)
¶
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)
)。
When threads are enabled, this function can only be called from the main thread; attempting to call it from other threads will cause a
ValueError
exception to be raised.
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)。
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.
信号。
sigpending
(
)
¶
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.
可用性：Unix (见手册页 sigpending(2) 了解进一步信息)。
另请参阅
pause()
,
pthread_sigmask()
and
sigwait()
.
3.3 版新增。
信号。
sigwait
(
sigset
)
¶
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.
可用性：Unix (见手册页 sigwait(3) 了解进一步信息)。
另请参阅
pause()
,
pthread_sigmask()
,
sigpending()
,
sigwaitinfo()
and
sigtimedwait()
.
3.3 版新增。
信号。
sigwaitinfo
(
sigset
)
¶
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
.
可用性：Unix (见手册页 sigwaitinfo(2) 了解进一步信息)。
另请参阅
pause()
,
sigwait()
and
sigtimedwait()
.
3.3 版新增。
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)。
信号。
sigtimedwait
(
sigset
,
timeout
)
¶
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.
可用性：Unix (见手册页 sigtimedwait(2) 了解进一步信息)。
另请参阅
pause()
,
sigwait()
and
sigwaitinfo()
.
3.3 版新增。
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.
import signal, os def handler(signum, frame): print('Signal handler called with signal', 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