On Friday, November 17, 2017 at 4:18:35 PM UTC-8, Dave S wrote: > > > > On Friday, November 17, 2017 at 1:29:55 PM UTC-8, Pierre wrote: >> >> No this won't work......I don't know how to instantiate a lock that will >> act as a global variable. this is an enigma. tried to read this: >> http://martin.kleppmann.com/2016/02/08/how-to-do-distributed-locking.html >> but it's too smart for me.....what i want is '*a lock for >> humans*'............like >> it's said in the publicity >> > > Distributed locks are for locking between multiple machines (like for > handling shards between ElasticSearch nodes). > > For thread safety, you only need to lock on one machine. You can use a > FIFO socket or or signals (Chapter 17 of the Python docs). Oh, and invite > a few philosophers to dinner. > > (The FIFO implementaton would be something like, > > while fifo.read() != token: > sleep(1) > if fifo.read() == token: > do dangerous work # keep this as short as possible > fifo.write(token) # then give token back ASAP > > sometimes the sleep() shoud be a busy wait, but probably not for a web > app. Busy waits are more common at driver level (the last time I did > that, I just used atomic reads and writes on a flag >
[sort of a baby version of a spinlock] > ). > > Oh, and obviously the fifo needs to have token at startup. > > fifo = socket(blah blah bleh) > fifo.open() > fifo.write(token) > > I haven't looked at your specific environment to see what extra > considerations are needed, and for so far for my apps it has been > sufficient to let the db engine handle locking (usually sqlite, which uses > a pretty coarse lock), so you may have holes in my advice. > > /dps > > -- Resources: - http://web2py.com - http://web2py.com/book (Documentation) - http://github.com/web2py/web2py (Source code) - https://code.google.com/p/web2py/issues/list (Report Issues) --- You received this message because you are subscribed to the Google Groups "web2py-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
