Support for scheduling jobs in the future

lib/queue_classic/queue.rb

@@ -41,6 +41,13 @@ def enqueue(method, *args)
       end
     end
 
+    def enqueue_at(time, method, *args)
+      QC.log_yield(:measure => 'queue.enqueue') do
+        s="INSERT INTO #{TABLE_NAME} (q_name, method, args, created_at) VALUES ($1, $2, $3, $4)"
+        res = conn_adapter.execute(s, name, method, JSON.dump(args), time)
+      end
+    end
+
     def lock
       QC.log_yield(:measure => 'queue.lock') do
         s = "SELECT * FROM lock_head($1, $2)"

sql/ddl.sql

@@ -19,6 +19,8 @@ BEGIN
     || ' WHERE locked_at IS NULL'
     || ' AND q_name = '
     || quote_literal(q_name)
+    || ' AND created_at <= '
+    || quote_literal(now())
     || ' LIMIT '
     || quote_literal(top_boundary)
     || ') limited'
@@ -37,6 +39,8 @@ BEGIN
         || ' WHERE locked_at IS NULL'
         || ' AND q_name = '
         || quote_literal(q_name)
+        || ' AND created_at <= '
+        || quote_literal(now())
         || ' ORDER BY id ASC'
         || ' LIMIT 1'
         || ' OFFSET ' || quote_literal(relative_top)

test/queue_test.rb

@@ -27,6 +27,16 @@ def test_lock_when_empty
     assert_nil(QC.lock)
   end
 
+  def test_lock_with_future_job
+    future = Time.now + 3
+    QC.enqueue_at(future, "Klass.method")
+    assert_nil QC.lock
+    until Time.now >= future do sleep 1 end
+    job = QC.lock
+    assert_equal("Klass.method", job[:method])
+    assert_equal([], job[:args])
+  end
+
   def test_count
     QC.enqueue("Klass.method")
     assert_equal(1, QC.count)