Commits on Aug 7, 2024

1. [PROF-10241] Use Process._fork hook in at_fork monkey patch on Ruby… …

   … 3.1+
   
   **What does this PR do?**
   
   This PR solves the long-standing "TODO" we had on the `at_fork` monkey
   patch where on Ruby 3.1+ there's a VM hook for instrumenting fork
   operations that avoids us needing to monkey patch `Kernel` and `Object`.
   
   To use the new hook we need to monkey patch `Process._fork` instead
   (see ruby/ruby#5017 and
   https://bugs.ruby-lang.org/issues/17795).
   
   Thus, I've added this monkey patch and disabled patching of
   `Kernel` and `Object` on Ruby 3.1+.
   
   **Motivation:**
   
   Avoid monkey patching core classes that no longer need to.
   
   **Additional Notes:**
   
   I'm not quite happy with either the AtForkMonkeyPatch or its specs, but
   I decided to not do a full revamp for now.
   
   **How to test the change?**
   
   This change includes test coverage.
   
   Here's a tiny test app that also exercises this feature:
   
   ```ruby
   puts RUBY_DESCRIPTION
   
   require 'datadog/core/utils/at_fork_monkey_patch'
   
   Datadog::Core::Utils::AtForkMonkeyPatch.apply!
   
   Process.datadog_at_fork(:child) { puts "Hello from child process: #{Process.pid} "}
   
   puts "Parent pid: #{Process.pid}"
   
   puts "fork { }"
   fork { }
   Process.wait
   
   puts "Kernel.fork { }"
   Kernel.fork { }
   Process.wait
   
   puts "Process.fork { }"
   Process.fork { }
   Process.wait
   
   puts "Foo.new.call"
   class Foo
     def call
       fork { }
     end
   
     def self.do_fork
       fork {  }
     end
   end
   Foo.new.call
   Process.wait
   
   puts "Foo.do_fork"
   Foo.do_fork
   Process.wait
   
   puts "Fork from outside"
   Foo.new.send(:fork) { }
   Process.wait
   
   class BasicFoo < BasicObject
     include ::Kernel
   
     def call
       fork { }
     end
   
     def self.do_fork
       fork { }
     end
   end
   
   puts "BasicFoo.new.call"
   BasicFoo.new.call
   Process.wait
   
   puts "BasicObject:"
   Class.new(BasicObject) { include(::Kernel); def call; fork { }; end }.new.call
   Process.wait
   
   puts "BasicFork.do_fork"
   BasicFoo.do_fork
   Process.wait
   ```
   
   P.s.: You may notice when you run this example on < 3.1 that
   `BasicFoo.new.call` and `BasicObject` are not instrumented!
   
   This was actually a known-gap from the old instrumentation.

   

   ivoanjo committed Aug 7, 2024
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2. Rename ProcessDaemonMonkeyPatch -> ProcessMonkeyPatch …

   We're now patching more than just `Process.daemon`.

   

   ivoanjo committed Aug 7, 2024
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3. Minor: Check pid before hash

   

   ivoanjo committed Aug 7, 2024
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