swarm: codebase split from go-ethereum (#1405)

network/priorityqueue/priorityqueue.go

@@ -0,0 +1,118 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+// package priority_queue implement a channel based priority queue
+// over arbitrary types. It provides an
+// an autopop loop applying a function to the items always respecting
+// their priority. The structure is only quasi consistent ie., if a lower
+// priority item is autopopped, it is guaranteed that there was a point
+// when no higher priority item was present, ie. it is not guaranteed
+// that there was any point where the lower priority item was present
+// but the higher was not
+
+package priorityqueue
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"github.com/ethereum/go-ethereum/metrics"
+)
+
+var (
+	ErrContention = errors.New("contention")
+
+	errBadPriority = errors.New("bad priority")
+
+	wakey = struct{}{}
+)
+
+// PriorityQueue is the basic structure
+type PriorityQueue struct {
+	Queues []chan interface{}
+	wakeup chan struct{}
+}
+
+// New is the constructor for PriorityQueue
+func New(n int, l int) *PriorityQueue {
+	var queues = make([]chan interface{}, n)
+	for i := range queues {
+		queues[i] = make(chan interface{}, l)
+	}
+	return &PriorityQueue{
+		Queues: queues,
+		wakeup: make(chan struct{}, 1),
+	}
+}
+
+// Run is a forever loop popping items from the queues
+func (pq *PriorityQueue) Run(ctx context.Context, f func(interface{})) {
+	top := len(pq.Queues) - 1
+	p := top
+READ:
+	for {
+		q := pq.Queues[p]
+		select {
+		case <-ctx.Done():
+			return
+		case x := <-q:
+			val := x.(struct {
+				v interface{}
+				t time.Time
+			})
+			f(val.v)
+			metrics.GetOrRegisterResettingTimer("pq.run", nil).UpdateSince(val.t)
+			p = top
+		default:
+			if p > 0 {
+				p--
+				continue READ
+			}
+			p = top
+			select {
+			case <-ctx.Done():
+				return
+			case <-pq.wakeup:
+			}
+		}
+	}
+}
+
+// Push pushes an item to the appropriate queue specified in the priority argument
+// if context is given it waits until either the item is pushed or the Context aborts
+func (pq *PriorityQueue) Push(x interface{}, p int) error {
+	if p < 0 || p >= len(pq.Queues) {
+		return errBadPriority
+	}
+	val := struct {
+		v interface{}
+		t time.Time
+	}{
+		x,
+		time.Now(),
+	}
+	select {
+	case pq.Queues[p] <- val:
+	default:
+		return ErrContention
+	}
+	select {
+	case pq.wakeup <- wakey:
+	default:
+	}
+	return nil
+}