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Diffstat (limited to 'Doc/library/signal.rst')
| -rw-r--r-- | Doc/library/signal.rst | 175 |
1 files changed, 169 insertions, 6 deletions
diff --git a/Doc/library/signal.rst b/Doc/library/signal.rst index d1cae13d62..84e283683d 100644 --- a/Doc/library/signal.rst +++ b/Doc/library/signal.rst @@ -36,7 +36,11 @@ at a later point(for example at the next :term:`bytecode` instruction). This has consequences: * It makes little sense to catch synchronous errors like :const:`SIGFPE` or - :const:`SIGSEGV`. + :const:`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 :mod:`faulthandler` module to report on synchronous + errors. * A long-running calculation implemented purely in C (such as regular expression matching on a large body of text) may run uninterrupted for an @@ -44,6 +48,9 @@ This has consequences: signal handlers will be called when the calculation finishes. +.. _signals-and-threads: + + Signals and threads ^^^^^^^^^^^^^^^^^^^ @@ -131,6 +138,28 @@ The variables defined in the :mod:`signal` module are: in user and kernel space. SIGPROF is delivered upon expiration. +.. data:: SIG_BLOCK + + A possible value for the *how* parameter to :func:`pthread_sigmask` + indicating that signals are to be blocked. + + .. versionadded:: 3.3 + +.. data:: SIG_UNBLOCK + + A possible value for the *how* parameter to :func:`pthread_sigmask` + indicating that signals are to be unblocked. + + .. versionadded:: 3.3 + +.. data:: SIG_SETMASK + + A possible value for the *how* parameter to :func:`pthread_sigmask` + indicating that the signal mask is to be replaced. + + .. versionadded:: 3.3 + + The :mod:`signal` module defines one exception: .. exception:: ItimerError @@ -138,7 +167,11 @@ The :mod:`signal` module defines one exception: Raised to signal an error from the underlying :func:`setitimer` or :func:`getitimer` implementation. Expect this error if an invalid interval timer or a negative time is passed to :func:`setitimer`. - This error is a subtype of :exc:`IOError`. + This error is a subtype of :exc:`OSError`. + + .. versionadded:: 3.3 + This error used to be a subtype of :exc:`IOError`, which is now an + alias of :exc:`OSError`. The :mod:`signal` module defines the following functions: @@ -172,6 +205,65 @@ The :mod:`signal` module defines the following functions: will then be called. Returns nothing. Not on Windows. (See the Unix man page :manpage:`signal(2)`.) + See also :func:`sigwait`, :func:`sigwaitinfo`, :func:`sigtimedwait` and + :func:`sigpending`. + + +.. function:: pthread_kill(thread_id, signum) + + Send the signal *signum* 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 :ref:`executed by the main + thread <signals-and-threads>`. Therefore, the only point of sending a signal to a particular + Python thread would be to force a running system call to fail with + :exc:`InterruptedError`. + + Use :func:`threading.get_ident()` or the :attr:`~threading.Thread.ident` + attribute of :class:`threading.Thread` objects to get a suitable value + for *thread_id*. + + If *signum* 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. + + Availability: Unix (see the man page :manpage:`pthread_kill(3)` for further + information). + + See also :func:`os.kill`. + + .. versionadded:: 3.3 + + +.. function:: 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. + + * :data:`SIG_BLOCK`: The set of blocked signals is the union of the current + set and the *mask* argument. + * :data:`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. + * :data:`SIG_SETMASK`: The set of blocked signals is set to the *mask* + argument. + + *mask* is a set of signal numbers (e.g. {:const:`signal.SIGINT`, + :const:`signal.SIGTERM`}). Use ``range(1, signal.NSIG)`` for a full mask + including all signals. + + For example, ``signal.pthread_sigmask(signal.SIG_BLOCK, [])`` reads the + signal mask of the calling thread. + + Availability: Unix. See the man page :manpage:`sigprocmask(3)` and + :manpage:`pthread_sigmask(3)` for further information. + + See also :func:`pause`, :func:`sigpending` and :func:`sigwait`. + + .. versionadded:: 3.3 + .. function:: setitimer(which, seconds[, interval]) @@ -201,13 +293,17 @@ The :mod:`signal` module defines the following functions: .. function:: set_wakeup_fd(fd) - Set the wakeup fd to *fd*. When a signal is received, a ``'\0'`` byte is - written to the fd. This can be used by a library to wakeup a poll or select - call, allowing the signal to be fully processed. + 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. *fd* must be non-blocking. It is up to the library to remove any bytes 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 :exc:`ValueError` exception to be raised. @@ -247,6 +343,73 @@ The :mod:`signal` module defines the following functions: :const:`SIGTERM`. A :exc:`ValueError` will be raised in any other case. +.. function:: 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. + + Availability: Unix (see the man page :manpage:`sigpending(2)` for further + information). + + See also :func:`pause`, :func:`pthread_sigmask` and :func:`sigwait`. + + .. versionadded:: 3.3 + + +.. function:: 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. + + Availability: Unix (see the man page :manpage:`sigwait(3)` for further + information). + + See also :func:`pause`, :func:`pthread_sigmask`, :func:`sigpending`, + :func:`sigwaitinfo` and :func:`sigtimedwait`. + + .. versionadded:: 3.3 + + +.. function:: 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 + :exc:`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 + :c:type:`siginfo_t` structure, namely: :attr:`si_signo`, :attr:`si_code`, + :attr:`si_errno`, :attr:`si_pid`, :attr:`si_uid`, :attr:`si_status`, + :attr:`si_band`. + + Availability: Unix (see the man page :manpage:`sigwaitinfo(2)` for further + information). + + See also :func:`pause`, :func:`sigwait` and :func:`sigtimedwait`. + + .. versionadded:: 3.3 + + +.. function:: sigtimedwait(sigset, timeout) + + Like :func:`sigwaitinfo`, but takes an additional *timeout* argument + specifying a timeout. If *timeout* is specified as :const:`0`, a poll is + performed. Returns :const:`None` if a timeout occurs. + + Availability: Unix (see the man page :manpage:`sigtimedwait(2)` for further + information). + + See also :func:`pause`, :func:`sigwait` and :func:`sigwaitinfo`. + + .. versionadded:: 3.3 + + .. _signal-example: Example @@ -263,7 +426,7 @@ be sent, and the handler raises an exception. :: def handler(signum, frame): print('Signal handler called with signal', signum) - raise IOError("Couldn't open device!") + raise OSError("Couldn't open device!") # Set the signal handler and a 5-second alarm signal.signal(signal.SIGALRM, handler) |