From: Joel VanderWerf <vjoel@...>
Date: 2004-01-17T16:16:38+09:00
Subject: faster Thread.exclusive


Ruby folks,

The following implementation of Thread.exclusive (called 
Thread.my_exclusive) seems to gain a bit on the thread.rb implementation:

                      user     system      total        real
warmup           0.300000   0.000000   0.300000 (  0.296724)
exclusive        7.000000   0.000000   7.000000 (  7.006737)
my_exclusive     5.040000   0.010000   5.050000 (  5.294778)
exclusive        6.950000   0.000000   6.950000 (  7.170255)
my_exclusive     4.970000   0.000000   4.970000 (  4.964166)

(850MHz PIII, linux 2.4.21, ruby 1.9.0)

Can anyone see any reason not to use it? There is slightly different 
semantics w.r.t. subclasses of Thread that redefine #critical, but I 
think the difference is benign. Also, there is no way that 
Thread.critical can raise an exception (in the curreny ruby source), so 
that's not going to cause a problem with the placement of the "old = 
critical" line.

The main reason I'm interested in this is some heavily threaded code 
that spends 20% of process time in Thread.exclusive (according to the 
profiler). I can probably improve this by using Thread.critical and 
Thread.critical= instead, but why not improve Thread.exclusive itself?

The new implementation (actually I've been using it for a year without 
knowing it was different from thread.rb) seems quite stable in my stress 
tests.

----

require 'thread'
require 'benchmark'

class Thread
   # Slightly faster (30%) replacement for Thread.exclusive.
   def self.my_exclusive
     old = critical
     self.critical = true
     yield
   ensure
     self.critical = old
   end
end

# ---- From thread.rb: ----
#
# class Thread
#   #
#   # FIXME: not documented in Pickaxe or Nutshell.
#   #
#   def Thread.exclusive
#     _old = Thread.critical
#     begin
#       Thread.critical = true
#       return yield
#     ensure
#       Thread.critical = _old
#     end
#   end
# end

Benchmark.bm(15) do |bm|

   n = 1_000_000

   bm.report "warmup" do
     n.times do
     end
   end

   bm.report "exclusive" do
     n.times do
       Thread.exclusive do
       end
     end
   end

   bm.report "my_exclusive" do
     n.times do
       Thread.my_exclusive do
       end
     end
   end

   bm.report "exclusive" do
     n.times do
       Thread.exclusive do
       end
     end
   end

   bm.report "my_exclusive" do
     n.times do
       Thread.my_exclusive do
       end
     end
   end

end