289 lines
6.8 KiB
Go
289 lines
6.8 KiB
Go
// Copyright 2019 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package enode
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import (
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"sync"
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"time"
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)
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// Iterator represents a sequence of nodes. The Next method moves to the next node in the
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// sequence. It returns false when the sequence has ended or the iterator is closed. Close
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// may be called concurrently with Next and Node, and interrupts Next if it is blocked.
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type Iterator interface {
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Next() bool // moves to next node
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Node() *Node // returns current node
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Close() // ends the iterator
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}
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// ReadNodes reads at most n nodes from the given iterator. The return value contains no
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// duplicates and no nil values. To prevent looping indefinitely for small repeating node
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// sequences, this function calls Next at most n times.
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func ReadNodes(it Iterator, n int) []*Node {
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seen := make(map[ID]*Node, n)
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for i := 0; i < n && it.Next(); i++ {
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// Remove duplicates, keeping the node with higher seq.
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node := it.Node()
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prevNode, ok := seen[node.ID()]
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if ok && prevNode.Seq() > node.Seq() {
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continue
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}
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seen[node.ID()] = node
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}
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result := make([]*Node, 0, len(seen))
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for _, node := range seen {
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result = append(result, node)
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}
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return result
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}
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// IterNodes makes an iterator which runs through the given nodes once.
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func IterNodes(nodes []*Node) Iterator {
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return &sliceIter{nodes: nodes, index: -1}
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}
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// CycleNodes makes an iterator which cycles through the given nodes indefinitely.
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func CycleNodes(nodes []*Node) Iterator {
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return &sliceIter{nodes: nodes, index: -1, cycle: true}
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}
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type sliceIter struct {
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mu sync.Mutex
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nodes []*Node
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index int
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cycle bool
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}
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func (it *sliceIter) Next() bool {
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it.mu.Lock()
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defer it.mu.Unlock()
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if len(it.nodes) == 0 {
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return false
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}
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it.index++
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if it.index == len(it.nodes) {
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if it.cycle {
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it.index = 0
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} else {
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it.nodes = nil
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return false
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}
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}
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return true
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}
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func (it *sliceIter) Node() *Node {
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it.mu.Lock()
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defer it.mu.Unlock()
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if len(it.nodes) == 0 {
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return nil
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}
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return it.nodes[it.index]
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}
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func (it *sliceIter) Close() {
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it.mu.Lock()
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defer it.mu.Unlock()
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it.nodes = nil
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}
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// Filter wraps an iterator such that Next only returns nodes for which
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// the 'check' function returns true.
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func Filter(it Iterator, check func(*Node) bool) Iterator {
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return &filterIter{it, check}
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}
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type filterIter struct {
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Iterator
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check func(*Node) bool
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}
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func (f *filterIter) Next() bool {
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for f.Iterator.Next() {
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if f.check(f.Node()) {
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return true
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}
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}
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return false
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}
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// FairMix aggregates multiple node iterators. The mixer itself is an iterator which ends
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// only when Close is called. Source iterators added via AddSource are removed from the
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// mix when they end.
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//
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// The distribution of nodes returned by Next is approximately fair, i.e. FairMix
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// attempts to draw from all sources equally often. However, if a certain source is slow
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// and doesn't return a node within the configured timeout, a node from any other source
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// will be returned.
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//
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// It's safe to call AddSource and Close concurrently with Next.
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type FairMix struct {
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wg sync.WaitGroup
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fromAny chan *Node
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timeout time.Duration
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cur *Node
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mu sync.Mutex
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closed chan struct{}
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sources []*mixSource
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last int
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}
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type mixSource struct {
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it Iterator
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next chan *Node
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timeout time.Duration
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}
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// NewFairMix creates a mixer.
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//
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// The timeout specifies how long the mixer will wait for the next fairly-chosen source
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// before giving up and taking a node from any other source. A good way to set the timeout
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// is deciding how long you'd want to wait for a node on average. Passing a negative
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// timeout makes the mixer completely fair.
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func NewFairMix(timeout time.Duration) *FairMix {
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m := &FairMix{
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fromAny: make(chan *Node),
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closed: make(chan struct{}),
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timeout: timeout,
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}
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return m
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}
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// AddSource adds a source of nodes.
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func (m *FairMix) AddSource(it Iterator) {
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m.mu.Lock()
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defer m.mu.Unlock()
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if m.closed == nil {
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return
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}
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m.wg.Add(1)
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source := &mixSource{it, make(chan *Node), m.timeout}
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m.sources = append(m.sources, source)
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go m.runSource(m.closed, source)
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}
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// Close shuts down the mixer and all current sources.
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// Calling this is required to release resources associated with the mixer.
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func (m *FairMix) Close() {
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m.mu.Lock()
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defer m.mu.Unlock()
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if m.closed == nil {
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return
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}
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for _, s := range m.sources {
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s.it.Close()
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}
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close(m.closed)
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m.wg.Wait()
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close(m.fromAny)
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m.sources = nil
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m.closed = nil
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}
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// Next returns a node from a random source.
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func (m *FairMix) Next() bool {
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m.cur = nil
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var timeout <-chan time.Time
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if m.timeout >= 0 {
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timer := time.NewTimer(m.timeout)
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timeout = timer.C
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defer timer.Stop()
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}
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for {
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source := m.pickSource()
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if source == nil {
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return m.nextFromAny()
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}
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select {
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case n, ok := <-source.next:
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if ok {
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m.cur = n
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source.timeout = m.timeout
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return true
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}
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// This source has ended.
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m.deleteSource(source)
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case <-timeout:
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source.timeout /= 2
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return m.nextFromAny()
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}
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}
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}
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// Node returns the current node.
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func (m *FairMix) Node() *Node {
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return m.cur
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}
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// nextFromAny is used when there are no sources or when the 'fair' choice
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// doesn't turn up a node quickly enough.
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func (m *FairMix) nextFromAny() bool {
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n, ok := <-m.fromAny
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if ok {
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m.cur = n
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}
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return ok
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}
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// pickSource chooses the next source to read from, cycling through them in order.
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func (m *FairMix) pickSource() *mixSource {
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m.mu.Lock()
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defer m.mu.Unlock()
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if len(m.sources) == 0 {
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return nil
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}
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m.last = (m.last + 1) % len(m.sources)
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return m.sources[m.last]
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}
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// deleteSource deletes a source.
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func (m *FairMix) deleteSource(s *mixSource) {
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m.mu.Lock()
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defer m.mu.Unlock()
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for i := range m.sources {
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if m.sources[i] == s {
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copy(m.sources[i:], m.sources[i+1:])
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m.sources[len(m.sources)-1] = nil
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m.sources = m.sources[:len(m.sources)-1]
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break
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}
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}
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}
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// runSource reads a single source in a loop.
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func (m *FairMix) runSource(closed chan struct{}, s *mixSource) {
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defer m.wg.Done()
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defer close(s.next)
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for s.it.Next() {
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n := s.it.Node()
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select {
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case s.next <- n:
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case m.fromAny <- n:
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case <-closed:
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return
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}
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}
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}
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