[Zope] How to prevent concurrent access to the same object?

[Dieter Maurer]

Alexei Ustyuzhaninov writes:
 > But generally RLock is inappropriate for this purpose in python. Take a 
 > look at this test for example:
 > 
 > 09:50:33 aleks@aiu:~/testRLock
 > $ cat test.py
 > import os
 > import threading
 > import time
 > 
 > lock=threading.RLock()
 > if os.fork()==0:
 >    # Child process
 >    time.sleep(1)
 >    lock.acquire()
 >    print "Process",os.getpid(),": the child acquired the lock"
 > else:
 >    # Parent process
 >    lock.acquire()
 >    print "Process",os.getpid(),": the parent acquired the lock"
 >    time.sleep(5)
 > lock.release()
 > print "Process",os.getpid(),"released the lock"
 > 
 > 09:52:46 aleks@aiu:~/testRLock
 > $ python test.py
 > Process 6164 : the parent acquired the lock
 > Process 6165 : the child acquired the lock
 > Process 6165 released the lock
 > Process 6164 released the lock
Please retry this with threads!

   While Linux uses processes to implement threads, these
   processes are more tightly coupled than those created by "fork".

   A fork'ed process has its own address space and its own independent
   resources (such as locks). Threads, on the other hand, share the
   same address space and the same resources.

   Locks will synchronize threads but not (independent) processes.


Dieter