Use Concurrent::Promises based TimerTask

Promises are the recommended infrastructure, replacing
several OG APIs, including TimerTasks.

SQ only uses TimerTasks in 3 places (currently) and
a very small subset of their overall functionality.
SolidQueue::TimerTask is a drop-in replacement.

This PR uses AtomicBoolean instead of the recommended
Concurrent::Cancellation to avoid a dependency on,
and the potential API stability issues of, edge features.

This completes the move from the old APIs to Promises and
makes all of the new concurrency features (Actors,
Channels, etc.) available for future SQ features and
enahancements.

Gemfile.lock

@@ -132,8 +132,6 @@ GEM
     rake (13.2.1)
     rdoc (6.8.1)
       psych (>= 4.0.0)
-    rdoc (6.6.3.1)
-      psych (>= 4.0.0)
     regexp_parser (2.9.2)
     reline (0.5.12)
       io-console (~> 0.5)

lib/solid_queue/dispatcher/concurrency_maintenance.rb

@@ -12,16 +12,10 @@ def initialize(interval, batch_size)
     end
 
     def start
-      @concurrency_maintenance_task = Concurrent::TimerTask.new(run_now: true, execution_interval: interval) do
+      @concurrency_maintenance_task = SolidQueue::TimerTask.new(run_now: true, execution_interval: interval) do
         expire_semaphores
         unblock_blocked_executions
       end
-
-      @concurrency_maintenance_task.add_observer do |_, _, error|
-        handle_thread_error(error) if error
-      end
-
-      @concurrency_maintenance_task.execute
     end
 
     def stop

lib/solid_queue/processes/registrable.rb

@@ -37,15 +37,9 @@ def registered?
       end
 
       def launch_heartbeat
-        @heartbeat_task = Concurrent::TimerTask.new(execution_interval: SolidQueue.process_heartbeat_interval) do
+        @heartbeat_task = SolidQueue::TimerTask.new(execution_interval: SolidQueue.process_heartbeat_interval) do
           wrap_in_app_executor { heartbeat }
         end
-
-        @heartbeat_task.add_observer do |_, _, error|
-          handle_thread_error(error) if error
-        end
-
-        @heartbeat_task.execute
       end
 
       def stop_heartbeat

lib/solid_queue/supervisor/maintenance.rb

@@ -7,16 +7,11 @@ module Supervisor::Maintenance
     end
 
     private
+
       def launch_maintenance_task
-        @maintenance_task = Concurrent::TimerTask.new(run_now: true, execution_interval: SolidQueue.process_alive_threshold) do
+        @maintenance_task = SolidQueue::TimerTask.new(run_now: true, execution_interval: SolidQueue.process_alive_threshold) do
           prune_dead_processes
         end
-
-        @maintenance_task.add_observer do |_, _, error|
-          handle_thread_error(error) if error
-        end
-
-        @maintenance_task.execute
       end
 
       def stop_maintenance_task

lib/solid_queue/timer_task.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module SolidQueue
+  class TimerTask
+    include AppExecutor
+
+    def initialize(execution_interval:, run_now: false, &block)
+      raise ArgumentError, "A block is required" unless block_given?
+      @shutdown = Concurrent::AtomicBoolean.new
+
+      run(run_now, execution_interval, &block)
+    end
+
+    def shutdown
+      @shutdown.make_true
+    end
+
+    private
+
+      def run(run_now, execution_interval, &block)
+        execute_task(&block) if run_now
+
+        Concurrent::Promises.future(execution_interval) do |interval|
+          repeating_task(interval, &block)
+        end.run
+      end
+
+      def execute_task(&block)
+        block.call unless @shutdown.true?
+      rescue Exception => e
+        handle_thread_error(e)
+      end
+
+      def repeating_task(interval, &block)
+        Concurrent::Promises.schedule(interval) do
+          execute_task(&block)
+        end.then do
+          repeating_task(interval, &block) unless @shutdown.true?
+        end
+      end
+  end
+end

test/unit/timer_task_test.rb

@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "mocha/minitest"
+
+class TimerTaskTest < ActiveSupport::TestCase
+  test "initialization requires a block" do
+    assert_raises(ArgumentError) do
+      SolidQueue::TimerTask.new(execution_interval: 1)
+    end
+  end
+
+  test "task runs immediate when run now true" do
+    executed = false
+
+    task = SolidQueue::TimerTask.new(run_now: true, execution_interval: 1) do
+      executed = true
+    end
+
+    sleep 0.1
+
+    assert executed, "Task should have executed immediately"
+    task.shutdown
+  end
+
+  test "task does not run immediately when run with run_now false" do
+    executed = false
+
+    task = SolidQueue::TimerTask.new(run_now: false, execution_interval: 1) do
+      executed = true
+    end
+
+    sleep 0.1
+
+    assert_not executed, "Task should have executed immediately"
+    task.shutdown
+  end
+
+  test "task repeats" do
+    executions = 0
+
+    task = SolidQueue::TimerTask.new(execution_interval: 0.1, run_now: false) do
+      executions += 1
+    end
+
+    sleep(0.5) # Wait to accumulate some executions
+
+    assert executions > 3, "The block should be executed repeatedly"
+
+    task.shutdown
+  end
+
+  test "task stops on shutdown" do
+    executions = 0
+
+    task = SolidQueue::TimerTask.new(execution_interval: 0.1, run_now: false) { executions += 1 }
+
+    sleep(0.3) # Let the task run a few times
+
+    task.shutdown
+
+    current_executions = executions
+
+    sleep(0.5) # Ensure no more executions after shutdown
+
+    assert_equal current_executions, executions, "The task should stop executing after shutdown"
+  end
+
+  test "calls handle_thread_error if task raises" do
+    task = SolidQueue::TimerTask.new(execution_interval: 0.1) do
+      raise ExpectedTestError.new
+    end
+    task.expects(:handle_thread_error).with(instance_of(ExpectedTestError))
+
+    sleep(0.2) # Give some time for the task to run and handle the error
+
+    task.shutdown
+  end
+end