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# frozen_string_literal: true
require 'thread'
begin
require 'concurrent'
rescue LoadError
# no problem, we'll fallback to our own map
end
module GraphQL
module Execution
class Lazy
# {GraphQL::Schema} uses this to match returned values to lazy resolution methods.
# Methods may be registered for classes, they apply to its subclasses also.
# The result of this lookup is cached for future resolutions.
# Instances of this class are thread-safe.
# @api private
# @see {Schema#lazy?} looks up values from this map
class LazyMethodMap
def initialize(use_concurrent: defined?(Concurrent::Map))
@storage = use_concurrent ? Concurrent::Map.new : ConcurrentishMap.new
end
def initialize_copy(other)
@storage = other.storage.dup
end
# @param lazy_class [Class] A class which represents a lazy value (subclasses may also be used)
# @param lazy_value_method [Symbol] The method to call on this class to get its value
def set(lazy_class, lazy_value_method)
@storage[lazy_class] = lazy_value_method
end
# @param value [Object] an object which may have a `lazy_value_method` registered for its class or superclasses
# @return [Symbol, nil] The `lazy_value_method` for this object, or nil
def get(value)
@storage.compute_if_absent(value.class) { find_superclass_method(value.class) }
end
def each
@storage.each_pair { |k, v| yield(k, v) }
end
protected
attr_reader :storage
private
def find_superclass_method(value_class)
@storage.each_pair { |lazy_class, lazy_value_method|
return lazy_value_method if value_class < lazy_class
}
nil
end
# Mock the Concurrent::Map API
class ConcurrentishMap
extend Forwardable
# Technically this should be under the mutex too,
# but I know it's only used when the lock is already acquired.
def_delegators :@storage, :each_pair, :size
def initialize
@semaphore = Mutex.new
# Access to this hash must always be managed by the mutex
# since it may be modified at runtime
@storage = {}
end
def []=(key, value)
@semaphore.synchronize {
@storage[key] = value
}
end
def compute_if_absent(key)
@semaphore.synchronize {
@storage.fetch(key) { @storage[key] = yield }
}
end
def initialize_copy(other)
@semaphore = Mutex.new
@storage = other.copy_storage
end
protected
def copy_storage
@semaphore.synchronize {
@storage.dup
}
end
end
end
end
end
end
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