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connpool.go
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connpool.go
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package main
import (
"context"
"net"
"sync"
"time"
)
type ConnFactory interface {
DialContext(context.Context) (WrappedConn, error)
}
type ConnPool struct {
size uint
ttl, backoff time.Duration
connfactory ConnFactory
waiters, prepared *RAQueue
qmux sync.Mutex
logger *CondLogger
ctx context.Context
cancel context.CancelFunc
shutdown sync.WaitGroup
}
type watchedConn struct {
conn net.Conn
cancel context.CancelFunc
canceldone chan struct{}
}
func NewConnPool(size uint, ttl, backoff time.Duration,
connfactory ConnFactory, logger *CondLogger) *ConnPool {
ctx, cancel := context.WithCancel(context.Background())
return &ConnPool{
size: size,
ttl: ttl,
backoff: backoff,
connfactory: connfactory,
waiters: NewRAQueue(),
prepared: NewRAQueue(),
logger: logger,
ctx: ctx,
cancel: cancel,
}
}
func (p *ConnPool) Start() {
p.shutdown.Add(int(p.size))
for i := uint(0); i < p.size; i++ {
go p.worker()
}
}
func (p *ConnPool) do_backoff() {
select {
case <-AfterWallClock(p.backoff):
case <-p.ctx.Done():
}
}
func (p *ConnPool) kill_prepared(queue_id uint, watched *watchedConn, output_ch chan *watchedConn) {
p.qmux.Lock()
deleted_elem := p.prepared.Delete(queue_id)
p.qmux.Unlock()
if deleted_elem == nil {
// Someone already grabbed this slot from queue. Dispatch anyway.
p.logger.Debug("Dead conn %v was grabbed from queue", watched.conn.LocalAddr())
output_ch <- watched
} else {
watched.conn.Close()
}
}
func (p *ConnPool) worker() {
defer p.shutdown.Done()
output_ch := make(chan *watchedConn)
dummybuf := make([]byte, 1)
for {
select {
case <-p.ctx.Done():
return
default:
}
conn, err := p.connfactory.DialContext(p.ctx)
if err != nil {
select {
case <-p.ctx.Done():
return
default:
p.logger.Error("Upstream connection error: %v", err)
p.do_backoff()
continue
}
}
localaddr := conn.LocalAddr()
p.logger.Debug("Established upstream connection %v", localaddr)
p.qmux.Lock()
waiter := p.waiters.Pop()
if waiter != nil {
p.qmux.Unlock()
waiter.(chan net.Conn) <- conn
p.logger.Warning("Pool connection delivered directly to waiter")
} else {
queue_id := p.prepared.Push(output_ch)
p.qmux.Unlock()
readctx, readcancel := context.WithCancel(p.ctx)
readdone := make(chan struct{}, 1)
go func() {
conn.ReadContext(readctx, dummybuf)
readdone <- struct{}{}
}()
watched := &watchedConn{conn, readcancel, readdone}
select {
// Connection delivered via queue
case output_ch <- watched:
p.logger.Debug("Pool connection %v delivered via queue", localaddr)
// Connection disrupted
case <-readdone:
p.logger.Debug("Pool connection %v was disrupted", localaddr)
p.kill_prepared(queue_id, watched, output_ch)
p.do_backoff()
// Expired
case <-AfterWallClock(p.ttl):
p.logger.Debug("Connection %v seem to be expired", localaddr)
p.kill_prepared(queue_id, watched, output_ch)
// Pool context cancelled
case <-p.ctx.Done():
conn.Close()
}
}
}
}
func (p *ConnPool) Get(ctx context.Context) chan net.Conn {
out := make(chan net.Conn, 1)
p.qmux.Lock()
free := p.prepared.Pop()
if free == nil {
waiter_ch := make(chan net.Conn, 1)
queue_id := p.waiters.Push(waiter_ch)
p.qmux.Unlock()
go func() {
select {
case <-ctx.Done():
out <- nil
// Try to remove conn request from waiter queue
p.qmux.Lock()
p.waiters.Delete(queue_id)
p.qmux.Unlock()
case <-p.ctx.Done():
out <- nil
case conn := <-waiter_ch:
out <- conn
}
}()
} else {
p.qmux.Unlock()
watched := <-(free.(chan *watchedConn))
watched.cancel()
<-watched.canceldone
out <- watched.conn
}
return out
}
func (p *ConnPool) Stop() {
p.cancel()
p.shutdown.Wait()
}