DEV: Prevent defer stats exception when thread aborted (#19863)

When the thread is aborted, an exception is raised before the `start` of a job is set, and therefore raises an exception in the `ensure` block. This commit checks that `start` exists, and also adds `abort_on_exception=true` so that this issue would have caused test failures.

lib/discourse.rb

@@ -191,6 +191,18 @@ module Discourse
 
   reset_job_exception_stats!
 
+  if Rails.env.test?
+    def self.catch_job_exceptions!
+      raise "tests only" if !Rails.env.test?
+      @catch_job_exceptions = true
+    end
+
+    def self.reset_catch_job_exceptions!
+      raise "tests only" if !Rails.env.test?
+      remove_instance_variable(:@catch_job_exceptions)
+    end
+  end
+
   # Log an exception.
   #
   # If your code is in a scheduled job, it is recommended to use the
@@ -220,7 +232,7 @@ module Discourse
       { current_db: cm.current_db, current_hostname: cm.current_hostname }.merge(context),
     )
 
-    raise ex if Rails.env.test?
+    raise ex if Rails.env.test? && !@catch_job_exceptions
   end
 
   # Expected less matches than what we got in a find

lib/scheduler/defer.rb

@@ -79,7 +79,11 @@ module Scheduler
     def start_thread
       @mutex.synchronize do
         @reactor = MessageBus::TimerThread.new if !@reactor
-        @thread = Thread.new { do_work while true } if !@thread&.alive?
+        @thread =
+          Thread.new do
+            @thread.abort_on_exception = true if Rails.env.test?
+            do_work while true
+          end if !@thread&.alive?
       end
     end
 
@@ -110,11 +114,13 @@ module Scheduler
       Discourse.handle_job_exception(ex, message: "Processing deferred code queue")
     ensure
       ActiveRecord::Base.connection_handler.clear_active_connections!
-      @stats_mutex.synchronize do
-        stats = @stats[desc]
-        if stats
-          stats[:finished] += 1
-          stats[:duration] += Process.clock_gettime(Process::CLOCK_MONOTONIC) - start
+      if start
+        @stats_mutex.synchronize do
+          stats = @stats[desc]
+          if stats
+            stats[:finished] += 1
+            stats[:duration] += Process.clock_gettime(Process::CLOCK_MONOTONIC) - start
+          end
         end
       end
     end

spec/lib/scheduler/defer_spec.rb

@@ -12,11 +12,15 @@ RSpec.describe Scheduler::Defer do
   end
 
   before do
+    Discourse.catch_job_exceptions!
     @defer = DeferInstance.new
     @defer.async = true
   end
 
-  after { @defer.stop! }
+  after do
+    @defer.stop!
+    Discourse.reset_catch_job_exceptions!
+  end
 
   it "supports basic instrumentation" do
     @defer.later("first") {}