Commits on Jan 31, 2024

1. Fix deadlock when logger tries to use correlation …

   **What does this PR do?**
   
   This PR fixes #3385 by preventing components initialization when
   calling the `Datadog::Tracing.correlation` API.
   
   Instead, we use the `allow_initialization: false` option, which was
   added exactly to help break these kinds of initialization cycles.
   
   **Motivation:**
   
   This fixes a deadlock issue such as:
   
   ```
   lib/datadog/core/configuration.rb:228:in `synchronize': deadlock; recursive locking (ThreadError)
     from lib/datadog/core/configuration.rb:228:in `safely_synchronize'
     from lib/datadog/core/configuration.rb:195:in `components'
     from lib/datadog/tracing.rb:134:in `components'
     from lib/datadog/tracing.rb:138:in `tracer'
     from lib/datadog/tracing.rb:76:in `correlation'
     from repro.rb:5:in `add'
     from logger-1.6.0/lib/logger.rb:691:in `debug'
     from lib/datadog/core/remote/component.rb:29:in `initialize'
     from lib/datadog/core/remote/component.rb:156:in `new'
     from lib/datadog/core/remote/component.rb:156:in `build'
     from lib/datadog/core/configuration/components.rb:90:in `initialize'
     from datadog-ci-0.7.0/lib/datadog/ci/configuration/components.rb:31:in `initialize'
     from lib/datadog/core/configuration.rb:248:in `new'
     from lib/datadog/core/configuration.rb:248:in `build_components'
     from lib/datadog/core/configuration.rb:89:in `block in configure'
     from lib/datadog/core/configuration.rb:230:in `block in safely_synchronize'
     from lib/datadog/core/configuration.rb:228:in `synchronize'
     from lib/datadog/core/configuration.rb:228:in `safely_synchronize'
     from lib/datadog/core/configuration.rb:84:in `configure'
     from lib/datadog/tracing/contrib/extensions.rb:64:in `configure'
     from repro.rb:9:in `<main>'
   ```
   
   that happens when a logger is configured to also print correlation
   
   **Additional Notes:**
   
   While it may seem that I've changed the API semantics by returning
   an `Identifier` when there is no tracer, the previous code was
   actually misleading.
   
   There is actually no way (that I know of) for `tracer` to be
   `nil` on dd-trace-rb currently. It can be disabled, but an instance
   will still exist.
   
   The disabled instance, when called, returns an empty `Identifier`,
   so here I'm replicating that behavior, without needing the
   components to be initialized.
   
   I guess this is open for debate? We could return `nil` instead
   in the future.
   
   **How to test the change?**
   
   This tiny snippet can be used to simulate the exact logger issue
   reported by the customer:
   
   ```ruby
   require 'ddtrace'
   
   class TestLogger < Datadog::Core::Logger
     def add(severity, message = nil, progname = nil, &block)
       puts Datadog::Tracing.correlation
     end
   end
   
   Datadog.configure do |c|
     c.logger.instance = TestLogger.new(STDOUT)
   end
   ```
   
   Fixes #3385

   

   ivoanjo committed Jan 31, 2024
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