From 0be5d5d4c4c26d28fd1f39496a7a88d208afff13 Mon Sep 17 00:00:00 2001
From: David Heinemeier Hansson <david@loudthinking.com>
Date: Mon, 1 Aug 2016 16:44:29 -0700
Subject: Add exponentially_longer and custom wait algorithms

---
 activejob/lib/active_job/exceptions.rb | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

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

diff --git a/activejob/lib/active_job/exceptions.rb b/activejob/lib/active_job/exceptions.rb
index 6b43a8bcb5..d4c973d3c1 100644
--- a/activejob/lib/active_job/exceptions.rb
+++ b/activejob/lib/active_job/exceptions.rb
@@ -12,7 +12,10 @@ module ActiveJob
       # holding queue for inspection.
       #
       # ==== Options
-      # * <tt>:wait</tt> - Re-enqueues the job with the specified delay in seconds (default: 3 seconds)
+      # * <tt>:wait</tt> - Re-enqueues the job with a delay specified either in seconds (default: 3 seconds), 
+      #   as a computing proc that the number of executions so far as an argument, or as a symbol reference of
+      #   <tt>:exponentially_longer<>, which applies the wait algorithm of <tt>(executions ** 4) + 2</tt>
+      #   (first wait 3s, then 18s, then 83s, etc)
       # * <tt>:attempts</tt> - Re-enqueues the job the specified number of times (default: 5 attempts)
       # * <tt>:queue</tt> - Re-enqueues the job on a different queue
       # * <tt>:priority</tt> - Re-enqueues the job with a different priority
@@ -20,9 +23,14 @@ module ActiveJob
       # ==== Examples
       #
       #  class RemoteServiceJob < ActiveJob::Base
-      #    retry_on Net::OpenTimeout, wait: 30.seconds, attempts: 10
+      #    retry_on CustomAppException # defaults to 3s wait, 5 attempts
+      #    retry_on AnotherCustomAppException, wait: ->(executions) { executions * 2 }
+      #    retry_on ActiveRecord::StatementInvalid, wait: 5.seconds, attempts: 3
+      #    retry_on Net::OpenTimeout, wait: :exponentially_longer, attempts: 10
       #
       #    def perform(*args)
+      #      # Might raise CustomAppException or AnotherCustomAppException for something domain specific
+      #      # Might raise ActiveRecord::StatementInvalid when a local db deadlock is detected
       #      # Might raise Net::OpenTimeout when the remote service is down
       #    end
       #  end
@@ -30,7 +38,7 @@ module ActiveJob
         rescue_from exception do |error|
           if executions < attempts
             logger.error "Retrying #{self.class} in #{wait} seconds, due to a #{exception}. The original exception was #{error.cause.inspect}."
-            retry_job wait: wait, queue: queue, priority: priority
+            retry_job wait: determine_delay(wait), queue: queue, priority: priority
           else
             logger.error "Stopped retrying #{self.class} due to a #{exception}, which reoccurred on #{executions} attempts. The original exception was #{error.cause.inspect}."
             raise error
@@ -81,5 +89,19 @@ module ActiveJob
     def retry_job(options = {})
       enqueue options
     end
+
+    private
+      def determine_delay(seconds_or_algorithm)
+        case seconds_or_algorithm
+        when :exponentially_longer
+          (executions ** 4) + 2
+        when Integer
+          seconds = seconds_or_algorithm
+          seconds
+        when Proc
+          algorithm = seconds_or_algorithm
+          algorithm.call(executions)
+        end
+      end  
   end
 end
-- 
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