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Validate AtomicFixnum update results before mutation #1114

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Validate AtomicFixnum update results before mutation #1114

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fe874f9
Validate AtomicFixnum update results
Aug 29, 2026
a9eaa98
Test invalid AtomicFixnum update results
OskarEichler Aug 30, 2026
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1 change: 1 addition & 0 deletions ext/concurrent-ruby-ext/atomic_fixnum.c
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,7 @@ VALUE method_atomic_fixnum_update(VALUE self) {
for (;;) {
old_value = method_atomic_fixnum_value(self);
new_value = rb_yield(old_value);
Check_Type(new_value, T_FIXNUM);
if (ir_compare_and_set(self, old_value, new_value) == Qtrue) {
return new_value;
}
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2 changes: 1 addition & 1 deletion lib/concurrent-ruby/concurrent/atomic/mutex_atomic_fixnum.rb
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Expand Up @@ -55,7 +55,7 @@ def compare_and_set(expect, update)
# @!macro atomic_fixnum_method_update
def update
synchronize do
@value = yield @value
ns_set(yield @value)
end
end

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11 changes: 11 additions & 0 deletions spec/concurrent/atomic/atomic_fixnum_spec.rb
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Expand Up @@ -152,6 +152,17 @@
atomic = described_class.new(1000)
expect(atomic.update { |v| v + 1 }).to eq 1001
end

it 'rejects a non-integer result without changing the value' do
atomic = described_class.new(1000)

expect {
atomic.update { 'not an integer' }
}.to(raise_error { |error|
expect(error.class).to be(ArgumentError).or(be(TypeError))

@bensheldon bensheldon Aug 30, 2026

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Can you be specific here? Why would it be 2 different kinds of error?

@OskarEichler OskarEichler Aug 31, 2026

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The two implementations already expose different validation errors: the C extension uses Ruby’s Check_Type(...), which raises TypeError, while MutexAtomicFixnum#ns_set delegates to NativeInteger.ensure_integer, which raises ArgumentError. This shared spec runs against both implementations, so it accepts the existing implementation-specific class while asserting the important invariant: the failed update does not mutate the value.

})
expect(atomic.value).to eq 1000
end
end
end

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