DEBUG-3457 start DI probe notifier worker on every event submission

Author: p

lib/datadog/di/probe_notifier_worker.rb

@@ -36,6 +36,7 @@ def initialize(settings, transport, logger, telemetry: nil)
         @sleep_remaining = nil
         @wake_scheduled = false
         @thread = nil
+        @pid = nil
         @flush = 0
       end
 
@@ -44,7 +45,7 @@ def initialize(settings, transport, logger, telemetry: nil)
       attr_reader :telemetry
 
       def start
-        return if @thread
+        return if @thread && @pid == Process.pid
         @thread = Thread.new do
           loop do
             # TODO If stop is requested, we stop immediately without
@@ -86,6 +87,7 @@ def start
             wake.wait(more ? min_send_interval : nil)
           end
         end
+        @pid = Process.pid
       end
 
       # Stops the background thread.
@@ -200,6 +202,10 @@ def io_in_progress?
               wake.signal
             end
           end
+
+          # Worker could be not running if the process forked - check and
+          # start it again in this case.
+          start
         end
 
         # Determine how much longer the worker thread should sleep