JezK
Edit File: adder.rb
module ThreadSafe module Util # A Ruby port of the Doug Lea's jsr166e.LondAdder class version 1.8 # available in public domain. # # Original source code available here: # http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/LongAdder.java?revision=1.8 # # One or more variables that together maintain an initially zero # sum. When updates (method +add+) are contended across threads, # the set of variables may grow dynamically to reduce contention. # Method +sum+ returns the current total combined across the # variables maintaining the sum. # # This class is usually preferable to single +Atomic+ reference when # multiple threads update a common sum that is used for purposes such # as collecting statistics, not for fine-grained synchronization # control. Under low update contention, the two classes have similar # characteristics. But under high contention, expected throughput of # this class is significantly higher, at the expense of higher space # consumption. class Adder < Striped64 # Adds the given value. def add(x) if (current_cells = cells) || !cas_base_computed {|current_base| current_base + x} was_uncontended = true hash = hash_code unless current_cells && (cell = current_cells.volatile_get_by_hash(hash)) && (was_uncontended = cell.cas_computed {|current_value| current_value + x}) retry_update(x, hash, was_uncontended) {|current_value| current_value + x} end end end def increment add(1) end def decrement add(-1) end # Returns the current sum. The returned value is _NOT_ an # atomic snapshot: Invocation in the absence of concurrent # updates returns an accurate result, but concurrent updates that # occur while the sum is being calculated might not be # incorporated. def sum x = base if current_cells = cells current_cells.each do |cell| x += cell.value if cell end end x end def reset internal_reset(0) end end end end