Ausgabe der neuen DB Einträge

venv/lib/python3.9/site-packages/twisted/internet/_signals.py

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+# -*- test-case-name: twisted.internet.test.test_sigchld -*-
+# Copyright (c) Twisted Matrix Laboratories.
+# See LICENSE for details.
+
+"""
+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<http://cr.yp.to/docs/selfpipe.html>}.
+
+From Python version 2.6, C{signal.siginterrupt} and C{signal.set_wakeup_fd}
+provide the necessary C signal handler which writes to the pipe to be
+registered with C{SA_RESTART}.
+"""
+
+from __future__ import division, absolute_import
+
+import signal
+
+
+def installHandler(fd):
+    """
+    Install a signal handler which will write a byte to C{fd} when
+    I{SIGCHLD} is received.
+
+    This is implemented by installing a SIGCHLD handler that does nothing,
+    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}
+    """
+    if fd == -1:
+        signal.signal(signal.SIGCHLD, signal.SIG_DFL)
+    else:
+        def noopSignalHandler(*args):
+            pass
+        signal.signal(signal.SIGCHLD, noopSignalHandler)
+        signal.siginterrupt(signal.SIGCHLD, False)
+    return signal.set_wakeup_fd(fd)
+
+
+
+def isDefaultHandler():
+    """
+    Determine whether the I{SIGCHLD} handler is the default or not.
+    """
+    return signal.getsignal(signal.SIGCHLD) == signal.SIG_DFL