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