[XMc@sdZddlZyddlmZmZWnek rIdZZnXyddlZWnek rsdZnXddlmZyddl m Z m Z Wnek rdZ Z nXdefdYZdZd Zd Zd Zd Zedk r$ed eZ eZ n`e dk rIede Z e Z n;edk rnedeZ eZ nedeZ eZ dS(s This module provides a uniform interface to the several mechanisms which are possibly available for dealing with signals. This module is used to integrate child process termination into a reactor event loop. This is a challenging feature to provide because most platforms indicate process termination via SIGCHLD and do not provide a way to wait for that signal and arbitrary I/O events at the same time. The naive implementation involves installing a Python SIGCHLD handler; unfortunately this leads to other syscalls being interrupted (whenever SIGCHLD is received) and failing with EINTR (which almost no one is prepared to handle). This interruption can be disabled via siginterrupt(2) (or one of the equivalent mechanisms); however, if the SIGCHLD is delivered by the platform to a non-main thread (not a common occurrence, but difficult to prove impossible), the main thread (waiting on select() or another event notification API) may not wake up leading to an arbitrary delay before the child termination is noticed. The basic solution to all these issues involves enabling SA_RESTART (ie, disabling system call interruption) and registering a C signal handler which writes a byte to a pipe. The other end of the pipe is registered with the event loop, allowing it to wake up shortly after SIGCHLD is received. See L{twisted.internet.posixbase._SIGCHLDWaker} for the implementation of the event loop side of this solution. The use of a pipe this way is known as the U{self-pipe trick}. The actual solution implemented in this module depends on the version of Python. From version 2.6, C{signal.siginterrupt} and C{signal.set_wakeup_fd} allow the necessary C signal handler which writes to the pipe to be registered with C{SA_RESTART}. Prior to 2.6, the L{twisted.internet._sigchld} extension module provides similar functionality. If neither of these is available, a Python signal handler is used instead. This is essentially the naive solution mentioned above and has the problems described there. iN(t set_wakeup_fdt siginterrupt(tmsg(tinstallHandlertisDefaultHandlert_HandlercBs eZdZdZdZRS(s L{_Handler} is a signal handler which writes a byte to a file descriptor whenever it is invoked. @ivar fd: The file descriptor to which to write. If this is C{None}, nothing will be written. cCs ||_dS(N(tfd(tselfR((s=/usr/lib/python2.7/dist-packages/twisted/internet/_signals.pyt__init__JscGs7|jdk r3ytj|jdWq3q3XndS(s L{_Handler.__call__} is the signal handler. It will write a byte to the wrapped file descriptor, if there is one. tN(RtNonetostwrite(Rtargs((s=/usr/lib/python2.7/dist-packages/twisted/internet/_signals.pyt__call__Ns (t__name__t __module__t__doc__RR(((s=/usr/lib/python2.7/dist-packages/twisted/internet/_signals.pyRBs cCs\|dkr'tjtjtj}ntjtjt|}t|trX|jSdS(sL Install a signal handler which will write a byte to C{fd} when I{SIGCHLD} is received. This is implemented by creating an instance of L{_Handler} with C{fd} and installing it as the signal handler. @param fd: The file descriptor to which to write when I{SIGCHLD} is received. @type fd: C{int} i(tsignaltSIGCHLDtSIG_DFLRt isinstanceR(Rtprevious((s=/usr/lib/python2.7/dist-packages/twisted/internet/_signals.pyt_installHandlerUsingSignal[s cCsX|dkr%tjtjtjn)tjtjtdttjtt|S(s Install a signal handler which will write a byte to C{fd} when I{SIGCHLD} is received. This is implemented by installing an instance of L{_Handler} wrapped around C{None}, setting the I{SIGCHLD} handler as not allowed to interrupt system calls, and using L{signal.set_wakeup_fd} to do the actual writing. @param fd: The file descriptor to which to write when I{SIGCHLD} is received. @type fd: C{int} iN(RRRRR RtFalseR(R((s=/usr/lib/python2.7/dist-packages/twisted/internet/_signals.pyt_installHandlerUsingSetWakeupqs  cCstjtjtjkS(sI Determine whether the I{SIGCHLD} handler is the default or not. (Rt getsignalRR(((s=/usr/lib/python2.7/dist-packages/twisted/internet/_signals.pyt_isDefaultHandlerscCstddS(s Fail to install a signal handler for I{SIGCHLD}. This implementation is used when the supporting code for the other implementations is unavailable (on Python versions 2.5 and older where neither the L{twisted.internet._sigchld} extension nor the standard L{signal} module is available). @param fd: Ignored; only for compatibility with the other implementations of this interface. @raise RuntimeError: Always raised to indicate no I{SIGCHLD} handler can be installed. s Cannot install a SIGCHLD handlerN(t RuntimeError(R((s=/usr/lib/python2.7/dist-packages/twisted/internet/_signals.pyt_cannotInstallHandlerscCstddS(NsNo usable signal API available(R(((s=/usr/lib/python2.7/dist-packages/twisted/internet/_signals.pyt_cannotDetermineDefaultssusing set_wakeup_fdsusing _sigchldsusing signal modulesnothing unavailable(RR RRRt ImportErrorR ttwisted.python.logRttwisted.internet._sigchldRt_extInstallHandlerRt_extIsDefaultHandlertobjectRRRRRR(((s=/usr/lib/python2.7/dist-packages/twisted/internet/_signals.pyt+sF