From 8b5c04e423cbfd90a15ed6fbab3f111803bc6544 Mon Sep 17 00:00:00 2001
From: David Heinemeier Hansson <david@loudthinking.com>
Date: Fri, 29 Jul 2016 13:54:55 -0700
Subject: Add retry_on/discard_on for better exception handling

---
 activejob/lib/active_job/exceptions.rb | 78 ++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 activejob/lib/active_job/exceptions.rb

(limited to 'activejob/lib/active_job/exceptions.rb')

diff --git a/activejob/lib/active_job/exceptions.rb b/activejob/lib/active_job/exceptions.rb
new file mode 100644
index 0000000000..4217b5dc65
--- /dev/null
+++ b/activejob/lib/active_job/exceptions.rb
@@ -0,0 +1,78 @@
+require 'active_job/arguments'
+
+module ActiveJob
+  # Provides behavior for retrying and discarding jobs on exceptions.
+  module Exceptions
+    extend ActiveSupport::Concern
+
+    module ClassMethods
+      # Catch the exception and reschedule job for re-execution after so many seconds, for a specific number of attempts.
+      # If the exception keeps getting raised beyond the specified number of attempts, the exception is allowed to 
+      # bubble up to the underlying queuing system, which may have its own retry mechanism or place it in a 
+      # holding queue for inspection.
+      #
+      # ==== Options
+      # * <tt>:wait</tt> - Re-enqueues the job with the specified delay in seconds
+      # * <tt>:attempts</tt> - Re-enqueues the job the specified number of times
+      #
+      # ==== Examples
+      #
+      #  class RemoteServiceJob < ActiveJob::Base
+      #    retry_on Net::OpenTimeout, wait: 30.seconds, attempts: 10
+      #
+      #    def perform(*args)
+      #      # Might raise Net::OpenTimeout when the remote service is down
+      #    end
+      #  end
+      def retry_on(exception, wait: 3.seconds, attempts: 5)
+        rescue_from exception do |error|
+          logger.error "Retrying #{self.class} in #{wait} seconds, due to a #{exception}. The original exception was #{error.cause.inspect}."
+          retry_job wait: wait if executions < attempts
+        end
+      end
+
+      # Discard the job with no attempts to retry, if the exception is raised. This is useful when the subject of the job,
+      # like an Active Record, is no longer available, and the job is thus no longer relevant.
+      #
+      # ==== Example
+      #
+      #  class SearchIndexingJob < ActiveJob::Base
+      #    discard_on ActiveJob::DeserializationError
+      #
+      #    def perform(record)
+      #      # Will raise ActiveJob::DeserializationError if the record can't be deserialized
+      #    end
+      #  end
+      def discard_on(exception)
+        rescue_from exception do |error|
+          logger.error "Discarded #{self.class} due to a #{exception}. The original exception was #{error.cause.inspect}."
+        end
+      end
+    end
+
+    # Reschedules the job to be re-executed. This is useful in combination
+    # with the +rescue_from+ option. When you rescue an exception from your job
+    # you can ask Active Job to retry performing your job.
+    #
+    # ==== Options
+    # * <tt>:wait</tt> - Enqueues the job with the specified delay in seconds
+    # * <tt>:wait_until</tt> - Enqueues the job at the time specified
+    # * <tt>:queue</tt> - Enqueues the job on the specified queue
+    # * <tt>:priority</tt> - Enqueues the job with the specified priority
+    #
+    # ==== Examples
+    #
+    #  class SiteScraperJob < ActiveJob::Base
+    #    rescue_from(ErrorLoadingSite) do
+    #      retry_job queue: :low_priority
+    #    end
+    #
+    #    def perform(*args)
+    #      # raise ErrorLoadingSite if cannot scrape
+    #    end
+    #  end
+    def retry_job(options = {})
+      enqueue options
+    end
+  end
+end
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