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✏️ Editing: _threadedselect.py

# -*- test-case-name: twisted.test.test_internet -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Threaded select reactor

The threadedselectreactor is a specialized reactor for integrating with
arbitrary foreign event loop, such as those you find in GUI toolkits.

There are three things you'll need to do to use this reactor.

Install the reactor at the beginning of your program, before importing
the rest of Twisted::

| from twisted.internet import _threadedselect
    | _threadedselect.install()

Interleave this reactor with your foreign event loop, at some point after
your event loop is initialized::

| from twisted.internet import reactor
    | reactor.interleave(foreignEventLoopWakerFunction)
    | self.addSystemEventTrigger('after', 'shutdown', foreignEventLoopStop)

Instead of shutting down the foreign event loop directly, shut down the
reactor::

| from twisted.internet import reactor
    | reactor.stop()

In order for Twisted to do its work in the main thread (the thread that
interleave is called from), a waker function is necessary.  The waker function
will be called from a "background" thread with one argument: func.
The waker function's purpose is to call func() from the main thread.
Many GUI toolkits ship with appropriate waker functions.
Some examples of this are wxPython's wx.callAfter (may be wxCallAfter in
older versions of wxPython) or PyObjC's PyObjCTools.AppHelper.callAfter.
These would be used in place of "foreignEventLoopWakerFunction" in the above
example.

The other integration point at which the foreign event loop and this reactor
must integrate is shutdown.  In order to ensure clean shutdown of Twisted,
you must allow for Twisted to come to a complete stop before quitting the
application.  Typically, you will do this by setting up an after shutdown
trigger to stop your foreign event loop, and call reactor.stop() where you
would normally have initiated the shutdown procedure for the foreign event
loop.  Shutdown functions that could be used in place of
"foreignEventloopStop" would be the ExitMainLoop method of the wxApp instance
with wxPython, or the PyObjCTools.AppHelper.stopEventLoop function.
"""

import select
import sys
from errno import EBADF, EINTR
from functools import partial
from queue import Empty, Queue
from threading import Thread

from zope.interface import implementer

from twisted.internet import posixbase
from twisted.internet.interfaces import IReactorFDSet
from twisted.internet.posixbase import _NO_FILEDESC, _NO_FILENO
from twisted.internet.selectreactor import _select
from twisted.python import failure, log, threadable

def dictRemove(dct, value):
    try:
        del dct[value]
    except KeyError:
        pass

def raiseException(e):
    raise e

@implementer(IReactorFDSet)
class ThreadedSelectReactor(posixbase.PosixReactorBase):
    """A threaded select() based reactor - runs on all POSIX platforms and on
    Win32.
    """

def __init__(self):
        threadable.init(1)
        self.reads = {}
        self.writes = {}
        self.toThreadQueue = Queue()
        self.toMainThread = Queue()
        self.workerThread = None
        self.mainWaker = None
        posixbase.PosixReactorBase.__init__(self)
        self.addSystemEventTrigger("after", "shutdown", self._mainLoopShutdown)

def wakeUp(self):
        # we want to wake up from any thread
        self.waker.wakeUp()

def callLater(self, *args, **kw):
        tple = posixbase.PosixReactorBase.callLater(self, *args, **kw)
        self.wakeUp()
        return tple

def _sendToMain(self, msg, *args):
        self.toMainThread.put((msg, args))
        if self.mainWaker is not None:
            self.mainWaker()

def _sendToThread(self, fn, *args):
        self.toThreadQueue.put((fn, args))

def _preenDescriptorsInThread(self):
        log.msg("Malformed file descriptor found.  Preening lists.")
        readers = self.reads.keys()
        writers = self.writes.keys()
        self.reads.clear()
        self.writes.clear()
        for selDict, selList in ((self.reads, readers), (self.writes, writers)):
            for selectable in selList:
                try:
                    select.select([selectable], [selectable], [selectable], 0)
                except BaseException:
                    log.msg("bad descriptor %s" % selectable)
                else:
                    selDict[selectable] = 1

def _workerInThread(self):
        try:
            while 1:
                fn, args = self.toThreadQueue.get()
                fn(*args)
        except SystemExit:
            pass  # Exception indicates this thread should exit
        except BaseException:
            f = failure.Failure()
            self._sendToMain("Failure", f)

def _doSelectInThread(self, timeout):
        """Run one iteration of the I/O monitor loop.

This will run all selectables who had input or output readiness
        waiting for them.
        """
        reads = self.reads
        writes = self.writes
        while 1:
            try:
                r, w, ignored = _select(reads.keys(), writes.keys(), [], timeout)
                break
            except ValueError:
                # Possibly a file descriptor has gone negative?
                log.err()
                self._preenDescriptorsInThread()
            except TypeError:
                # Something *totally* invalid (object w/o fileno, non-integral
                # result) was passed
                log.err()
                self._preenDescriptorsInThread()
            except OSError as se:
                # select(2) encountered an error
                if se.args[0] in (0, 2):
                    # windows does this if it got an empty list
                    if (not reads) and (not writes):
                        return
                    else:
                        raise
                elif se.args[0] == EINTR:
                    return
                elif se.args[0] == EBADF:
                    self._preenDescriptorsInThread()
                else:
                    # OK, I really don't know what's going on.  Blow up.
                    raise
        self._sendToMain("Notify", r, w)

def _process_Notify(self, r, w):
        reads = self.reads
        writes = self.writes

_drdw = self._doReadOrWrite
        _logrun = log.callWithLogger
        for selectables, method, dct in ((r, "doRead", reads), (w, "doWrite", writes)):
            for selectable in selectables:
                # if this was disconnected in another thread, kill it.
                if selectable not in dct:
                    continue
                # This for pausing input when we're not ready for more.
                _logrun(selectable, _drdw, selectable, method, dct)

def _process_Failure(self, f):
        f.raiseException()

_doIterationInThread = _doSelectInThread

def ensureWorkerThread(self):
        if self.workerThread is None or not self.workerThread.isAlive():
            self.workerThread = Thread(target=self._workerInThread)
            self.workerThread.start()

def doThreadIteration(self, timeout):
        self._sendToThread(self._doIterationInThread, timeout)
        self.ensureWorkerThread()
        msg, args = self.toMainThread.get()
        getattr(self, "_process_" + msg)(*args)

doIteration = doThreadIteration

def _interleave(self):
        while self.running:
            self.runUntilCurrent()
            t2 = self.timeout()
            t = self.running and t2
            self._sendToThread(self._doIterationInThread, t)
            yield None
            msg, args = self.toMainThread.get_nowait()
            getattr(self, "_process_" + msg)(*args)

def interleave(self, waker, *args, **kw):
        """
        interleave(waker) interleaves this reactor with the
        current application by moving the blocking parts of
        the reactor (select() in this case) to a separate
        thread.  This is typically useful for integration with
        GUI applications which have their own event loop
        already running.

See the module docstring for more information.
        """
        self.startRunning(*args, **kw)
        loop = self._interleave()

def mainWaker(waker=waker, loop=loop):
            waker(partial(next, loop))

self.mainWaker = mainWaker
        next(loop)
        self.ensureWorkerThread()

def _mainLoopShutdown(self):
        self.mainWaker = None
        if self.workerThread is not None:
            self._sendToThread(raiseException, SystemExit)
            self.wakeUp()
            try:
                while 1:
                    msg, args = self.toMainThread.get_nowait()
            except Empty:
                pass
            self.workerThread.join()
            self.workerThread = None
        try:
            while 1:
                fn, args = self.toThreadQueue.get_nowait()
                if fn is self._doIterationInThread:
                    log.msg("Iteration is still in the thread queue!")
                elif fn is raiseException and args[0] is SystemExit:
                    pass
                else:
                    fn(*args)
        except Empty:
            pass

def _doReadOrWrite(self, selectable, method, dict):
        try:
            why = getattr(selectable, method)()
            handfn = getattr(selectable, "fileno", None)
            if not handfn:
                why = _NO_FILENO
            elif handfn() == -1:
                why = _NO_FILEDESC
        except BaseException:
            why = sys.exc_info()[1]
            log.err()
        if why:
            self._disconnectSelectable(selectable, why, method == "doRead")

def addReader(self, reader):
        """Add a FileDescriptor for notification of data available to read."""
        self._sendToThread(self.reads.__setitem__, reader, 1)
        self.wakeUp()

def addWriter(self, writer):
        """Add a FileDescriptor for notification of data available to write."""
        self._sendToThread(self.writes.__setitem__, writer, 1)
        self.wakeUp()

def removeReader(self, reader):
        """Remove a Selectable for notification of data available to read."""
        self._sendToThread(dictRemove, self.reads, reader)

def removeWriter(self, writer):
        """Remove a Selectable for notification of data available to write."""
        self._sendToThread(dictRemove, self.writes, writer)

def removeAll(self):
        return self._removeAll(self.reads, self.writes)

def getReaders(self):
        return list(self.reads.keys())

def getWriters(self):
        return list(self.writes.keys())

def stop(self):
        """
        Extend the base stop implementation to also wake up the select thread so
        that C{runUntilCurrent} notices the reactor should stop.
        """
        posixbase.PosixReactorBase.stop(self)
        self.wakeUp()

def run(self, installSignalHandlers=True):
        self.startRunning(installSignalHandlers=installSignalHandlers)
        self.mainLoop()

def mainLoop(self):
        q = Queue()
        self.interleave(q.put)
        while self.running:
            try:
                q.get()()
            except StopIteration:
                break

def install():
    """Configure the twisted mainloop to be run using the select() reactor."""
    reactor = ThreadedSelectReactor()
    from twisted.internet.main import installReactor

installReactor(reactor)
    return reactor

__all__ = ["install"]

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