Add Unique Queue infrastructure and move TestPullRequests to this (#9856)

* Upgrade levelqueue to version 0.2.0

This adds functionality for Unique Queues

* Add UniqueQueue interface and functions to create them

* Add UniqueQueue implementations

* Move TestPullRequests over to use UniqueQueue

* Reduce code duplication

* Add bytefifos

* Ensure invalid types are logged

* Fix close race in PersistableChannelQueue Shutdown

1 files changed, 29 insertions, 0 deletions

diff --git a/modules/queue/unique_queue.go b/modules/queue/unique_queue.go
new file mode 100644
index 0000000000..87e0594ecf
--- /dev/null
+++ b/modules/queue/unique_queue.go
@@ -0,0 +1,29 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package queue
+
+import (
+	"fmt"
+)
+
+// UniqueQueue defines a queue which guarantees only one instance of same
+// data is in the queue. Instances with same identity will be
+// discarded if there is already one in the line.
+//
+// This queue is particularly useful for preventing duplicated task
+// of same purpose - please note that this does not guarantee that a particular
+// task cannot be processed twice or more at the same time. Uniqueness is
+// only guaranteed whilst the task is waiting in the queue.
+//
+// Users of this queue should be careful to push only the identifier of the
+// data
+type UniqueQueue interface {
+	Queue
+	PushFunc(Data, func() error) error
+	Has(Data) (bool, error)
+}
+
+// ErrAlreadyInQueue is returned when trying to push data to the queue that is already in the queue
+var ErrAlreadyInQueue = fmt.Errorf("already in queue")