class Concurrent::ThreadSafe::Util::Adder

A Ruby port of the Doug Lea's jsr166e.LondAdder class version 1.8 available in public domain.

Original source code available here: 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.

@!visibility private

Public Instance Methods

add(x) click to toggle source

Adds the given value.

# File lib/concurrent-ruby/concurrent/thread_safe/util/adder.rb, line 35
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
decrement() click to toggle source
# File lib/concurrent-ruby/concurrent/thread_safe/util/adder.rb, line 49
def decrement
  add(-1)
end
increment() click to toggle source
# File lib/concurrent-ruby/concurrent/thread_safe/util/adder.rb, line 45
def increment
  add(1)
end
reset() click to toggle source
# File lib/concurrent-ruby/concurrent/thread_safe/util/adder.rb, line 68
def reset
  internal_reset(0)
end
sum() click to toggle source

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.

# File lib/concurrent-ruby/concurrent/thread_safe/util/adder.rb, line 58
def sum
  x = base
  if current_cells = cells
    current_cells.each do |cell|
      x += cell.value if cell
    end
  end
  x
end