defer to thread in gevent

thread.py

import gevent, gevent.event
import threading, Queue, collections, time, functools

def _threads_poller_f():
    while _OsThread._threads_count:
        try:
            t, rv, isexc = _OsThread._threads_results.get_nowait()
        except Queue.Empty:
            gevent.sleep()
        else:
            if isexc:
                t._async_result.set_exception(rv)
            else:
                t._async_result.set(rv)

class _OsThread(threading.Thread):
    _threads_count = 0
    _threads_sleep_interval = 0.008
    _threads_timeout = 3
    _threads_poller = None
    _threads_results = Queue.Queue()
    _free_threads = collections.deque()
    _free_threads_lock = threading.RLock()

    def __init__(self):
        "Do not instantiate _OsThread objects directly. Use acquire instead."
        threading.Thread.__init__(self)
        self.setDaemon(True)
        self.stopped = False
        self.inq = Queue.Queue()

    def _init(self):
        self.free = False
        _OsThread._threads_count += 1
        if _OsThread._threads_count == 1:
            _OsThread._threads_poller = gevent.spawn_raw(_threads_poller_f)

    def __enter__(self):
        return self

    def __exit__(self, type, value, tb):
        self.release()

    @classmethod
    def acquire(cls):
        with _OsThread._free_threads_lock:
            try:
                self = _OsThread._free_threads.popleft()
                self._init()
            except IndexError:
                self = cls()
                self._init()
                self.start()
        return self

    def release(self):
        with _OsThread._free_threads_lock:
            if not self.free and not self.stopped:
                _OsThread._threads_count -= 1
                self.free = True
                _OsThread._free_threads.append(self)
        return self

    def stop(self):
        with _OsThread._free_threads_lock:
            self.stopped = True
            if self.free:
                self.free = False
                _OsThread._free_threads.remove(self)
            else:
                _OsThread._threads_count -= 1
        self.inq.put(None)
        return self


    # Overridden
    def run(self):
        while True:
            time.sleep(_OsThread._threads_sleep_interval)
            try:
                obj = self.inq.get(timeout=_OsThread._threads_timeout)
            except Queue.Empty:
                with _OsThread._free_threads_lock:
                    if self.free:
                        self.free = False
                        _OsThread._free_threads.remove(self)
                        break
                    else:
                        continue
            if obj is None:
                break
            else:
                rv = None
                isexc = False
                try:
                    rv = obj.func(*obj.args, **obj.kwargs)
                except Exception as e:
                    rv = e
                    isexc = True
                finally:
                    _OsThread._threads_results.put((obj, rv, isexc))

osthread_acquire = _OsThread.acquire


class inthread(object):
    def __new__(cls, f, *args, **kwargs):
        self = object.__new__(cls)
        if isinstance(f, _OsThread):
            self.func = args[0]
            self.args = args[1:]
            self.kwargs = kwargs
            self._async_result = gevent.event.AsyncResult()
            self.thread = f
            self.thread.inq.put(self)
            return self._async_result.get()
        else:
            self.func = f
            self.args = args
            self.kwargs = kwargs
            self._async_result = gevent.event.AsyncResult()
            self.thread = _OsThread.acquire()
            self.thread.inq.put(self)
            try:
                return self._async_result.get()
            finally:
                self.thread.release()

    @classmethod
    def wrap(cls, func):
        @functools.wraps(func)
        def wrapped(*args, **kwargs):
            return cls(func, *args, **kwargs)
        return wrapped