well-goknown/vendor/github.com/valyala/fasthttp/lbclient.go

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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
// 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
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// Clients must contain non-zero clients list.
// Incoming requests are balanced among these clients.
Clients []BalancingClient
cs []*lbClient
// Timeout is the request timeout used when calling LBClient.Do.
//
// DefaultLBClientTimeout is used by default.
Timeout time.Duration
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mu sync.RWMutex
once sync.Once
}
// 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
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// 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)
}
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// 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,
})
}
}
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// 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)
}
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// 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()
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t := atomic.LoadUint64(&c.total)
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
)