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class GVLFuture
PENDING = Object.new
def initialize
@lock = Mutex.new
@condition = ConditionVariable.new
@value = PENDING
end
def complete?(value = @value)
value != PENDING
end
def value
value = @value
return value if complete? value
@lock.synchronize do
# recheck complete?
@condition.wait @lock unless complete? @value
end
@value
end
def fulfill(value)
# why not check complete? before synchronizing?
@lock.synchronize do
raise 'already fulfilled' if complete?
@value = value
@condition.broadcast
self
end
end
end
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