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FEATURE: add interface compatible constant version of thread local var #823
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45 changes: 45 additions & 0 deletions
45
lib/concurrent-ruby/concurrent/atomic/constant_thread_local_var.rb
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,45 @@ | ||
require 'concurrent/atomic/abstract_thread_local_var' | ||
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module Concurrent | ||
# Has the same interface as {ThreadLocalVar} but the value can never be changed. | ||
# The value is always the default provided to the constructor. | ||
class ConstantThreadLocalVar < AbstractThreadLocalVar | ||
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# @note the value is always equal to default value | ||
# @!macro thread_local_var_method_get | ||
def value | ||
default | ||
end | ||
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# @!macro thread_local_var_method_set | ||
# @raise ArgumentError if the value is not equal to the default | ||
def value=(value) | ||
if value != default | ||
raise ArgumentError, "Constant thread local vars may not be altered" | ||
end | ||
end | ||
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# @!macro thread_local_var_method_bind | ||
# @raise ArgumentError if the value is not equal to the default | ||
def bind(value) | ||
self.value = value | ||
if block_given? | ||
yield | ||
end | ||
end | ||
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protected | ||
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def allocate_storage | ||
# nothing to do | ||
end | ||
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def default | ||
if @default_block | ||
@default_block.call | ||
else | ||
@default | ||
end | ||
end | ||
end | ||
end |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,56 @@ | ||
require 'rbconfig' | ||
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module Concurrent | ||
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require 'concurrent/atomic/constant_thread_local_var' | ||
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RSpec.describe ConstantThreadLocalVar do | ||
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context "#value" do | ||
it 'can return default value' do | ||
v = described_class.new("apple") | ||
expect(v.value).to eq("apple") | ||
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v = described_class.new do | ||
"orange" | ||
end | ||
expect(v.value).to eq("orange") | ||
end | ||
end | ||
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context "#value=" do | ||
it 'can set value to same value' do | ||
v = described_class.new("apple") | ||
v.value = "apple" | ||
end | ||
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it 'will raise an ArgumentError when attempting to change immutable value' do | ||
v = described_class.new do | ||
"apple" | ||
end | ||
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expect do | ||
v.value = "orange" | ||
end.to raise_error(ArgumentError) | ||
end | ||
end | ||
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context '#bind' do | ||
it 'will raise when attempting to bind to a different value' do | ||
v = described_class.new("apple") | ||
expect do | ||
v.bind("orange") {} | ||
end.to raise_error(ArgumentError) | ||
end | ||
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it 'works when bind value is the same' do | ||
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v = described_class.new("apple") | ||
v.bind("apple") do | ||
expect(v.value).to eq("apple") | ||
end | ||
end | ||
end | ||
end | ||
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end |
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This evaluates the
@default_block
on each value read, so it may return different values each time value is called. I think that if thedefault_block
is provided the ConstantThreadLocalVar should still store the computed value per thread (since it might differ). So the implementation could inherit from ThreadLocalVar, disallow usingvalue=
, and it would be good if it optimises@default
case (the value is equal for all threads).