Crashes quickly on my Ubuntu machine when _ssl is not imported and there at least 3 threads. Reducing threads or importing _ssl seems to work around the race. _ssl happens to setup locking callbacks OpenSSL wants to do multi-threading safely. I think this will still crash if we import a different OpenSSL to the one the Python implementation is l…

crypto_thread_crash.py

import thread
import threading
import struct
import itertools

import cryptography.hazmat.backends

# UNCOMMENT THIS TO POSSIBLY STOP CRASHES
#import _ssl


def randloop():
    s = b.ffi.new("char[]", 16)
    sb = b.ffi.buffer(s)
    sb[:] = b"\0" * 16

    for i in itertools.count():
        b.lib.RAND_seed(s, 16)

        if i % 10000 == 0:
            print thread.get_ident(), i


b = cryptography.hazmat.backends.default_backend()
threads = []


print "Starting..."


for x in range(3):
    t = threading.Thread(target=randloop)
    t.daemon = True
    t.start()
    threads.append(t)


print "Waiting..."


while threads:
    for t in threads:
        t.join(0.1)