1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
|
package fasthttp
import (
"sync"
"sync/atomic"
"time"
)
// BalancingClient is the interface for clients, which may be passed
// to LBClient.Clients.
type BalancingClient interface {
DoDeadline(req *Request, resp *Response, deadline time.Time) error
PendingRequests() int
}
// LBClient balances requests among available LBClient.Clients.
//
// It has the following features:
//
// - Balances load among available clients using 'least loaded' + 'least total'
// hybrid technique.
// - Dynamically decreases load on unhealthy clients.
//
// It is forbidden copying LBClient instances. Create new instances instead.
//
// It is safe calling LBClient methods from concurrently running goroutines.
type LBClient struct {
noCopy noCopy
// Clients must contain non-zero clients list.
// Incoming requests are balanced among these clients.
Clients []BalancingClient
// HealthCheck is a callback called after each request.
//
// The request, response and the error returned by the client
// is passed to HealthCheck, so the callback may determine whether
// the client is healthy.
//
// Load on the current client is decreased if HealthCheck returns false.
//
// By default HealthCheck returns false if err != nil.
HealthCheck func(req *Request, resp *Response, err error) bool
// Timeout is the request timeout used when calling LBClient.Do.
//
// DefaultLBClientTimeout is used by default.
Timeout time.Duration
cs []*lbClient
once sync.Once
mu sync.RWMutex
}
// DefaultLBClientTimeout is the default request timeout used by LBClient
// when calling LBClient.Do.
//
// The timeout may be overridden via LBClient.Timeout.
const DefaultLBClientTimeout = time.Second
// DoDeadline calls DoDeadline on the least loaded client.
func (cc *LBClient) DoDeadline(req *Request, resp *Response, deadline time.Time) error {
return cc.get().DoDeadline(req, resp, deadline)
}
// DoTimeout calculates deadline and calls DoDeadline on the least loaded client.
func (cc *LBClient) DoTimeout(req *Request, resp *Response, timeout time.Duration) error {
deadline := time.Now().Add(timeout)
return cc.get().DoDeadline(req, resp, deadline)
}
// Do calculates timeout using LBClient.Timeout and calls DoTimeout
// on the least loaded client.
func (cc *LBClient) Do(req *Request, resp *Response) error {
timeout := cc.Timeout
if timeout <= 0 {
timeout = DefaultLBClientTimeout
}
return cc.DoTimeout(req, resp, timeout)
}
func (cc *LBClient) init() {
cc.mu.Lock()
defer cc.mu.Unlock()
if len(cc.Clients) == 0 {
// developer sanity-check
panic("BUG: LBClient.Clients cannot be empty")
}
for _, c := range cc.Clients {
cc.cs = append(cc.cs, &lbClient{
c: c,
healthCheck: cc.HealthCheck,
})
}
}
// AddClient adds a new client to the balanced clients and
// returns the new total number of clients.
func (cc *LBClient) AddClient(c BalancingClient) int {
cc.mu.Lock()
cc.cs = append(cc.cs, &lbClient{
c: c,
healthCheck: cc.HealthCheck,
})
cc.mu.Unlock()
return len(cc.cs)
}
// RemoveClients removes clients using the provided callback.
// If rc returns true, the passed client will be removed.
// Returns the new total number of clients.
func (cc *LBClient) RemoveClients(rc func(BalancingClient) bool) int {
cc.mu.Lock()
n := 0
for idx, cs := range cc.cs {
cc.cs[idx] = nil
if rc(cs.c) {
continue
}
cc.cs[n] = cs
n++
}
cc.cs = cc.cs[:n]
cc.mu.Unlock()
return len(cc.cs)
}
func (cc *LBClient) get() *lbClient {
cc.once.Do(cc.init)
cc.mu.RLock()
cs := cc.cs
minC := cs[0]
minN := minC.PendingRequests()
minT := atomic.LoadUint64(&minC.total)
for _, c := range cs[1:] {
n := c.PendingRequests()
t := atomic.LoadUint64(&c.total) /* #nosec G601 */
if n < minN || (n == minN && t < minT) {
minC = c
minN = n
minT = t
}
}
cc.mu.RUnlock()
return minC
}
type lbClient struct {
c BalancingClient
healthCheck func(req *Request, resp *Response, err error) bool
penalty uint32
// total amount of requests handled.
total uint64
}
func (c *lbClient) DoDeadline(req *Request, resp *Response, deadline time.Time) error {
err := c.c.DoDeadline(req, resp, deadline)
if !c.isHealthy(req, resp, err) && c.incPenalty() {
// Penalize the client returning error, so the next requests
// are routed to another clients.
time.AfterFunc(penaltyDuration, c.decPenalty)
} else {
atomic.AddUint64(&c.total, 1)
}
return err
}
func (c *lbClient) PendingRequests() int {
n := c.c.PendingRequests()
m := atomic.LoadUint32(&c.penalty)
return n + int(m)
}
func (c *lbClient) isHealthy(req *Request, resp *Response, err error) bool {
if c.healthCheck == nil {
return err == nil
}
return c.healthCheck(req, resp, err)
}
func (c *lbClient) incPenalty() bool {
m := atomic.AddUint32(&c.penalty, 1)
if m > maxPenalty {
c.decPenalty()
return false
}
return true
}
func (c *lbClient) decPenalty() {
atomic.AddUint32(&c.penalty, ^uint32(0))
}
const (
maxPenalty = 300
penaltyDuration = 3 * time.Second
)
|
