[Mailman-Developers] Subscribers suddenly"disappear"

Mark Sapiro mark at msapiro.net
Fri Aug 22 22:34:47 CEST 2008

Hash: SHA1

Mark Sapiro wrote:

> Stephen J. Turnbull wrote:
>> Mark Sapiro writes:
>>  > 1) add_member saves the list with the first member.
>>  > 2) VirginRunner gets there first, instantiates and caches the list.
>>  >    It then locks the list, processes the welcome and saves and unlocks
>>  >    the list.
>>  > 3) add_member gets the lock, adds the second member and saves the list.
>>  > 4) Virgin runner gets the second welcome. The list is cached, so it
>>  >    uses the cached instance. It then locks the list which ultimately
>>  >    calls MailList.__load() to refresh the list data, but __load()
>>  >    does
>>  > 
>>  >             mtime = os.path.getmtime(dbfile)
>>  >             if mtime <= self.__timestamp:
>>  >                 # File is not newer
>>  >                 return None, None
>> Shouldn't "mtime < self.__timestamp" do the right thing (much more
>> often)?
> I didn't reply sooner because when I first saw this, I didn't read it
> carefully, and I didn't "get" what Stephen was saying. Then I had to
> think about it.
> I have concluded that barring resetting of clocks backward, "mtime <
> self.__timestamp" is equivalent to "False". Whenever a config.pck is
> written or read in a process, __timestamp is set to the current mod time
> of the config.pck. Thus, the value of self.__timestamp for a cached list
> object is always <= mtime.

I have thought about this some more and have come up with the attached
patch which I have tested with Max's script and propose for Mailman 2.2.

The patch changes the '<=' test to '<' as Stephen suggests, but then so
it won't effectively disable ever not reloading the config.pck, it
changes the setting of __timestamp following a successful read from the
mod time of the config.pck to the current time truncated to an int.

Thus, once we've read a config.pck that's more than a second old, a
subsequent load of the same object will skip rereading the config.pck if
it wasn't updated in the interim.

- --
Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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