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Mark sender thread as fork safe for Puma #315

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Mark sender thread as fork safe for Puma #315

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2 changes: 2 additions & 0 deletions lib/datadog/statsd/sender.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,8 @@ def start
# start background thread
@sender_thread = @thread_class.new(&method(:send_loop))
@sender_thread.name = "Statsd Sender" unless Gem::Version.new(RUBY_VERSION) < Gem::Version.new('2.3')
# advise multi-threaded app servers to ignore this thread for the purposes of fork safety warnings
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@marcotc marcotc Jan 6, 2026

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Can you add a link to Puma, so we know who's reading this variable?
Something like: https://github.com/puma/puma/blob/5937d8953a154d69cab13887cc361eef9d7df2a4/lib/puma/cluster.rb#L374

@sender_thread.thread_variable_set(:fork_safe, true)
rescue ThreadError => e
@logger.debug { "Statsd: Failed to start sender thread: #{e.message}" } if @logger
@mx.synchronize { @done = true }
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11 changes: 9 additions & 2 deletions spec/statsd/sender_spec.rb
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Expand Up @@ -48,6 +48,13 @@
|thds| thds.any? { |t| t.name == "Statsd Sender" }
}
end

it 'marks the sender thread as fork safe' do
subject.start
expect(Thread.list).to satisfy {
|thds| thds.any? { |t| t.name == "Statsd Sender" && t.thread_variable_get(:fork_safe) }
}
end
end

context 'when the sender is started' do
Expand Down Expand Up @@ -204,9 +211,9 @@

let(:thread_class) do
if Thread.instance_methods.include?(:name=)
fake_thread = instance_double(Thread, { "alive?" => true, "name=" => true, "join" => true })
fake_thread = instance_double(Thread, { "alive?" => true, "name=" => true, "join" => true, "thread_variable_set" => true })
else
fake_thread = instance_double(Thread, { "alive?" => true, "join" => true })
fake_thread = instance_double(Thread, { "alive?" => true, "join" => true, "thread_variable_set" => true })
end
class_double(Thread, new: fake_thread)
end
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