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# one thread, one mutex (no contention) require 'thread' m = Thread::Mutex.new r = 0 max = 2000 lmax = max * max (1..1).map{ Thread.new{ i = 0 while i<lmax i += 1 m.synchronize{ r += 1 } end } }.each{|e| e.join } raise r.to_s if r != max * max