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# Python modules
import time
import mmap
import os
import sys
PY_MAJOR_VERSION = sys.version_info[0]
# hashlib is only available in Python >= 2.5. I still want to support
# older Pythons so I import md5 if hashlib is not available. Fortunately
# md5 can masquerade as hashlib for my purposes.
try:
import hashlib
except ImportError:
import md5 as hashlib
# 3rd party modules
import posix_ipc
# Utils for this demo
import utils
PY_MAJOR_VERSION = sys.version_info[0]
utils.say("Oooo 'ello, I'm Mrs. Conclusion!")
params = utils.read_params()
# Mrs. Premise has already created the semaphore and shared memory.
# I just need to get handles to them.
memory = posix_ipc.SharedMemory(params["SHARED_MEMORY_NAME"])
semaphore = posix_ipc.Semaphore(params["SEMAPHORE_NAME"])
# MMap the shared memory
mapfile = mmap.mmap(memory.fd, memory.size)
# Once I've mmapped the file descriptor, I can close it without
# interfering with the mmap. This also demonstrates that os.close() is a
# perfectly legitimate alternative to the SharedMemory's close_fd() method.
os.close(memory.fd)
what_i_wrote = ""
for i in range(0, params["ITERATIONS"]):
utils.say("iteration %d" % i)
if not params["LIVE_DANGEROUSLY"]:
# Wait for Mrs. Premise to free up the semaphore.
utils.say("Waiting to acquire the semaphore")
semaphore.acquire()
s = utils.read_from_memory(mapfile)
while s == what_i_wrote:
if not params["LIVE_DANGEROUSLY"]:
# Release the semaphore...
utils.say("Releasing the semaphore")
semaphore.release()
# ...and wait for it to become available again.
utils.say("Waiting to acquire the semaphore")
semaphore.acquire()
s = utils.read_from_memory(mapfile)
if what_i_wrote:
if PY_MAJOR_VERSION > 2:
what_i_wrote = what_i_wrote.encode()
try:
assert(s == hashlib.md5(what_i_wrote).hexdigest())
except AssertionError:
utils.raise_error(AssertionError,
"Shared memory corruption after %d iterations." % i)
if PY_MAJOR_VERSION > 2:
s = s.encode()
what_i_wrote = hashlib.md5(s).hexdigest()
utils.write_to_memory(mapfile, what_i_wrote)
if not params["LIVE_DANGEROUSLY"]:
utils.say("Releasing the semaphore")
semaphore.release()
semaphore.close()
mapfile.close()
utils.say("")
utils.say("%d iterations complete" % (i + 1))
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