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##############################################################################
#
# Copyright (c) 2001-2005 Zope Foundation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.1 (ZPL). A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE
#
##############################################################################
import asyncore
import os
import socket
import errno
import threading
# Wake up a call to select() running in the main thread.
#
# This is useful in a context where you are using Medusa's I/O
# subsystem to deliver data, but the data is generated by another
# thread. Normally, if Medusa is in the middle of a call to
# select(), new output data generated by another thread will have
# to sit until the call to select() either times out or returns.
# If the trigger is 'pulled' by another thread, it should immediately
# generate a READ event on the trigger object, which will force the
# select() invocation to return.
#
# A common use for this facility: letting Medusa manage I/O for a
# large number of connections; but routing each request through a
# thread chosen from a fixed-size thread pool. When a thread is
# acquired, a transaction is performed, but output data is
# accumulated into buffers that will be emptied more efficiently
# by Medusa. [picture a server that can process database queries
# rapidly, but doesn't want to tie up threads waiting to send data
# to low-bandwidth connections]
#
# The other major feature provided by this class is the ability to
# move work back into the main thread: if you call pull_trigger()
# with a thunk argument, when select() wakes up and receives the
# event it will call your thunk from within that thread. The main
# purpose of this is to remove the need to wrap thread locks around
# Medusa's data structures, which normally do not need them. [To see
# why this is true, imagine this scenario: A thread tries to push some
# new data onto a channel's outgoing data queue at the same time that
# the main thread is trying to remove some]
class _triggerbase(object):
"""OS-independent base class for OS-dependent trigger class."""
kind = None # subclass must set to "pipe" or "loopback"; used by repr
def __init__(self):
self._closed = False
# `lock` protects the `thunks` list from being traversed and
# appended to simultaneously.
self.lock = threading.Lock()
# List of no-argument callbacks to invoke when the trigger is
# pulled. These run in the thread running the asyncore mainloop,
# regardless of which thread pulls the trigger.
self.thunks = []
def readable(self):
return True
def writable(self):
return False
def handle_connect(self):
pass
def handle_close(self):
self.close()
# Override the asyncore close() method, because it doesn't know about
# (so can't close) all the gimmicks we have open. Subclass must
# supply a _close() method to do platform-specific closing work. _close()
# will be called iff we're not already closed.
def close(self):
if not self._closed:
self._closed = True
self.del_channel()
self._close() # subclass does OS-specific stuff
def pull_trigger(self, thunk=None):
if thunk:
with self.lock:
self.thunks.append(thunk)
self._physical_pull()
def handle_read(self):
try:
self.recv(8192)
except (OSError, socket.error):
return
with self.lock:
for thunk in self.thunks:
try:
thunk()
except:
nil, t, v, tbinfo = asyncore.compact_traceback()
self.log_info(
'exception in trigger thunk: (%s:%s %s)' %
(t, v, tbinfo))
self.thunks = []
if os.name == 'posix':
class trigger(_triggerbase, asyncore.file_dispatcher):
kind = "pipe"
def __init__(self, map):
_triggerbase.__init__(self)
r, self.trigger = self._fds = os.pipe()
asyncore.file_dispatcher.__init__(self, r, map=map)
def _close(self):
for fd in self._fds:
os.close(fd)
self._fds = []
def _physical_pull(self):
os.write(self.trigger, b'x')
else: # pragma: no cover
# Windows version; uses just sockets, because a pipe isn't select'able
# on Windows.
class trigger(_triggerbase, asyncore.dispatcher):
kind = "loopback"
def __init__(self, map):
_triggerbase.__init__(self)
# Get a pair of connected sockets. The trigger is the 'w'
# end of the pair, which is connected to 'r'. 'r' is put
# in the asyncore socket map. "pulling the trigger" then
# means writing something on w, which will wake up r.
w = socket.socket()
# Disable buffering -- pulling the trigger sends 1 byte,
# and we want that sent immediately, to wake up asyncore's
# select() ASAP.
w.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
count = 0
while True:
count += 1
# Bind to a local port; for efficiency, let the OS pick
# a free port for us.
# Unfortunately, stress tests showed that we may not
# be able to connect to that port ("Address already in
# use") despite that the OS picked it. This appears
# to be a race bug in the Windows socket implementation.
# So we loop until a connect() succeeds (almost always
# on the first try). See the long thread at
# http://mail.zope.org/pipermail/zope/2005-July/160433.html
# for hideous details.
a = socket.socket()
a.bind(("127.0.0.1", 0))
connect_address = a.getsockname() # assigned (host, port) pair
a.listen(1)
try:
w.connect(connect_address)
break # success
except socket.error as detail:
if detail[0] != errno.WSAEADDRINUSE:
# "Address already in use" is the only error
# I've seen on two WinXP Pro SP2 boxes, under
# Pythons 2.3.5 and 2.4.1.
raise
# (10048, 'Address already in use')
# assert count <= 2 # never triggered in Tim's tests
if count >= 10: # I've never seen it go above 2
a.close()
w.close()
raise RuntimeError("Cannot bind trigger!")
# Close `a` and try again. Note: I originally put a short
# sleep() here, but it didn't appear to help or hurt.
a.close()
r, addr = a.accept() # r becomes asyncore's (self.)socket
a.close()
self.trigger = w
asyncore.dispatcher.__init__(self, r, map=map)
def _close(self):
# self.socket is r, and self.trigger is w, from __init__
self.socket.close()
self.trigger.close()
def _physical_pull(self):
self.trigger.send(b'x')