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On old FreeBSD versions, concurrent.futures cannot be used. I don't remember why, it's probably related to semaphores (something like a low hardcoded limit). See for example first lines of Lib/test/test_concurrent_futures.py:
---
# Skip tests if _multiprocessing wasn't built. 
test.support.import_module('_multiprocessing') 
# Skip tests if sem_open implementation is broken. 
test.support.import_module('multiprocessing.synchronize')
# import threading after _multiprocessing to raise a more revelant error 
# message: "No module named _multiprocessing". _multiprocessing is not compiled
# without thread support.
test.support.import_module('threading')
---
The problem is that asyncio always try to import concurrent.futures. Example: 
http://buildbot.python.org/all/builders/x86%20FreeBSD%206.4%203.x/builds/4213/steps/test/logs/stdio
test test_asyncio crashed -- Traceback (most recent call last):
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/test/regrtest.py", line 1276, in runtest_inner
 test_runner()
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/test/test_asyncio/__init__.py", line 31, in test_main
 run_unittest(suite())
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/test/test_asyncio/__init__.py", line 21, in suite
 __import__(mod_name)
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/test/test_asyncio/test_base_events.py", line 11, in <module>
 from asyncio import base_events
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/asyncio/__init__.py", line 21, in <module>
 from .futures import *
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/asyncio/futures.py", line 21, in <module>
 Error = concurrent.futures._base.Error
AttributeError: 'module' object has no attribute 'futures'