From 47778f2d2fb27745d52c1221739ecc5d2f8af667 Mon Sep 17 00:00:00 2001
From: Thorsten Eckel <te@znuny.com>
Date: Fri, 29 Nov 2019 16:48:21 +0100
Subject: [PATCH] Follow up - 2c8825b387445fc9aaaa945433aaf94851540375 -
 ActiveJobLock lock update fails due to ActiveRecord::Deadlocked
 "Mysql2::Error: Deadlock found when trying to get lock; try restarting
 transaction" exception.

---
 app/jobs/concerns/has_active_job_lock.rb      |  4 ++++
 .../jobs/concerns/has_active_job_lock_spec.rb | 21 +++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/app/jobs/concerns/has_active_job_lock.rb b/app/jobs/concerns/has_active_job_lock.rb
index 9931a4c11..563e7a1ef 100644
--- a/app/jobs/concerns/has_active_job_lock.rb
+++ b/app/jobs/concerns/has_active_job_lock.rb
@@ -95,6 +95,10 @@ module HasActiveJobLock
     # but it's safe to retry as described in the docs:
     # https://www.postgresql.org/docs/10/transaction-iso.html
     e.message.include?('PG::TRSerializationFailure') ? retry : raise
+  rescue ActiveRecord::Deadlocked => e
+    # MySQL handles lock race condition differently and raises a Deadlock exception:
+    # Mysql2::Error: Deadlock found when trying to get lock; try restarting transaction
+    e.message.include?('Mysql2::Error: Deadlock found when trying to get lock') ? retry : raise
   rescue ActiveRecord::RecordNotUnique
     existing_active_job_lock!
   end
diff --git a/spec/jobs/concerns/has_active_job_lock_spec.rb b/spec/jobs/concerns/has_active_job_lock_spec.rb
index 4e8ae77e5..362d0d23b 100644
--- a/spec/jobs/concerns/has_active_job_lock_spec.rb
+++ b/spec/jobs/concerns/has_active_job_lock_spec.rb
@@ -121,6 +121,27 @@ RSpec.describe HasActiveJobLock, type: :job do
         expect(exception_raised).to be true
       end
     end
+
+    context "when ActiveRecord::Deadlocked 'Mysql2::Error: Deadlock found when trying to get lock; try restarting transaction' is raised" do
+
+      it 'retries execution until succeed' do
+        allow(ActiveRecord::Base.connection).to receive(:open_transactions).and_return(0)
+        allow(ActiveJobLock).to receive(:transaction).and_call_original
+        exception_raised = false
+        allow(ActiveJobLock).to receive(:transaction).with(isolation: :serializable) do |&block|
+
+          if !exception_raised
+            exception_raised = true
+            raise ActiveRecord::Deadlocked, 'Mysql2::Error: Deadlock found when trying to get lock; try restarting transaction'
+          end
+
+          block.call
+        end
+
+        expect { job_class.perform_later }.to have_enqueued_job(job_class).exactly(:once)
+        expect(exception_raised).to be true
+      end
+    end
   end
 
   include_examples 'handle locking of jobs'