From: Joel VanderWerf <vjoel@...>
Date: 2003-01-13T06:11:13+09:00
Subject: waiting for a file lock without blocking other threads


Is there a way to wait for a file lock without blocking other threads in 
the same ruby process? The best I could come up with is

     if Thread.list.size == 1
       flock(LOCK_EX)
     else
       period = 0.001
       until flock(LOCK_SH|LOCK_NB)
         sleep period
         period *= 2 if period < 1
       end
     end

(I'm using the exponential so that it checks frequently for a while, but 
  gradually uses less and less cpu, down to once per second.)

I guess this really boils down to not having native threads. What I was 
looking for was something like #select, but for file locks. But I can't 
see how that would be implemented without the ruby interpreter being 
thread-safe.

A related question:

There are warnings that flock doesn't work correctly with Linux NFS, and 
that fcntl should be used instead. Anyone have any experience with this?