gevent exceptions are ignored while blocking on queries

Gevent exceptions — like Timeout — appear to be ignored while a query is active.

Example follows.

Note that a Timeout should be raised after 2 second, but instead it is raised after 5 seconds, and the main thread is blocked (even to ^C) after 2 seconds:

$ python test.py
ping: 0.5
ping: 1.0
ping: 1.5
================================================================================
ELAPSED: 5.0
================================================================================
Traceback (most recent call last):
    …
gevent.timeout.Timeout: 2 seconds

test.py:

import time

from gevent import monkey
monkey.patch_all(subprocess=True)

from psycogreen.gevent import patch_psycopg
patch_psycopg()

import psycopg2

import gevent

start = time.time()

def spinner():
    while True:
        gevent.sleep(0.5)
        print "ping: %0.01f" %(time.time() - start)

try:
    gevent.spawn(spinner)
    gevent.Timeout(2).start()
    cxn = psycopg2.connect("host=localhost")
    cur = cxn.cursor()
    cur.execute("select pg_sleep(5)")
finally:
    print "=" * 80
    print "ELAPSED: %0.01f" %(time.time() - start)
    print "=" * 80

Tested on OS X 10.8.4 and Linux + epoll.

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