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/*
*
* Copyright 2016 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package grpclb
import (
"fmt"
"sync"
"time"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/connectivity"
"google.golang.org/grpc/resolver"
)
// The parent ClientConn should re-resolve when grpclb loses connection to the
// remote balancer. When the ClientConn inside grpclb gets a TransientFailure,
// it calls lbManualResolver.ResolveNow(), which calls parent ClientConn's
// ResolveNow, and eventually results in re-resolve happening in parent
// ClientConn's resolver (DNS for example).
//
// parent
// ClientConn
// +-----------------------------------------------------------------+
// | parent +---------------------------------+ |
// | DNS ClientConn | grpclb | |
// | resolver balancerWrapper | | |
// | + + | grpclb grpclb | |
// | | | | ManualResolver ClientConn | |
// | | | | + + | |
// | | | | | | Transient | |
// | | | | | | Failure | |
// | | | | | <--------- | | |
// | | | <--------------- | ResolveNow | | |
// | | <--------- | ResolveNow | | | | |
// | | ResolveNow | | | | | |
// | | | | | | | |
// | + + | + + | |
// | +---------------------------------+ |
// +-----------------------------------------------------------------+
// lbManualResolver is used by the ClientConn inside grpclb. It's a manual
// resolver with a special ResolveNow() function.
//
// When ResolveNow() is called, it calls ResolveNow() on the parent ClientConn,
// so when grpclb client lose contact with remote balancers, the parent
// ClientConn's resolver will re-resolve.
type lbManualResolver struct {
scheme string
ccr resolver.ClientConn
ccb balancer.ClientConn
}
func (r *lbManualResolver) Build(_ resolver.Target, cc resolver.ClientConn, _ resolver.BuildOption) (resolver.Resolver, error) {
r.ccr = cc
return r, nil
}
func (r *lbManualResolver) Scheme() string {
return r.scheme
}
// ResolveNow calls resolveNow on the parent ClientConn.
func (r *lbManualResolver) ResolveNow(o resolver.ResolveNowOption) {
r.ccb.ResolveNow(o)
}
// Close is a noop for Resolver.
func (*lbManualResolver) Close() {}
// NewAddress calls cc.NewAddress.
func (r *lbManualResolver) NewAddress(addrs []resolver.Address) {
r.ccr.NewAddress(addrs)
}
// NewServiceConfig calls cc.NewServiceConfig.
func (r *lbManualResolver) NewServiceConfig(sc string) {
r.ccr.NewServiceConfig(sc)
}
const subConnCacheTime = time.Second * 10
// lbCacheClientConn is a wrapper balancer.ClientConn with a SubConn cache.
// SubConns will be kept in cache for subConnCacheTime before being removed.
//
// Its new and remove methods are updated to do cache first.
type lbCacheClientConn struct {
cc balancer.ClientConn
timeout time.Duration
mu sync.Mutex
// subConnCache only keeps subConns that are being deleted.
subConnCache map[resolver.Address]*subConnCacheEntry
subConnToAddr map[balancer.SubConn]resolver.Address
}
type subConnCacheEntry struct {
sc balancer.SubConn
cancel func()
abortDeleting bool
}
func newLBCacheClientConn(cc balancer.ClientConn) *lbCacheClientConn {
return &lbCacheClientConn{
cc: cc,
timeout: subConnCacheTime,
subConnCache: make(map[resolver.Address]*subConnCacheEntry),
subConnToAddr: make(map[balancer.SubConn]resolver.Address),
}
}
func (ccc *lbCacheClientConn) NewSubConn(addrs []resolver.Address, opts balancer.NewSubConnOptions) (balancer.SubConn, error) {
if len(addrs) != 1 {
return nil, fmt.Errorf("grpclb calling NewSubConn with addrs of length %v", len(addrs))
}
addrWithoutMD := addrs[0]
addrWithoutMD.Metadata = nil
ccc.mu.Lock()
defer ccc.mu.Unlock()
if entry, ok := ccc.subConnCache[addrWithoutMD]; ok {
// If entry is in subConnCache, the SubConn was being deleted.
// cancel function will never be nil.
entry.cancel()
delete(ccc.subConnCache, addrWithoutMD)
return entry.sc, nil
}
scNew, err := ccc.cc.NewSubConn(addrs, opts)
if err != nil {
return nil, err
}
ccc.subConnToAddr[scNew] = addrWithoutMD
return scNew, nil
}
func (ccc *lbCacheClientConn) RemoveSubConn(sc balancer.SubConn) {
ccc.mu.Lock()
defer ccc.mu.Unlock()
addr, ok := ccc.subConnToAddr[sc]
if !ok {
return
}
if entry, ok := ccc.subConnCache[addr]; ok {
if entry.sc != sc {
// This could happen if NewSubConn was called multiple times for the
// same address, and those SubConns are all removed. We remove sc
// immediately here.
delete(ccc.subConnToAddr, sc)
ccc.cc.RemoveSubConn(sc)
}
return
}
entry := &subConnCacheEntry{
sc: sc,
}
ccc.subConnCache[addr] = entry
timer := time.AfterFunc(ccc.timeout, func() {
ccc.mu.Lock()
if entry.abortDeleting {
return
}
ccc.cc.RemoveSubConn(sc)
delete(ccc.subConnToAddr, sc)
delete(ccc.subConnCache, addr)
ccc.mu.Unlock()
})
entry.cancel = func() {
if !timer.Stop() {
// If stop was not successful, the timer has fired (this can only
// happen in a race). But the deleting function is blocked on ccc.mu
// because the mutex was held by the caller of this function.
//
// Set abortDeleting to true to abort the deleting function. When
// the lock is released, the deleting function will acquire the
// lock, check the value of abortDeleting and return.
entry.abortDeleting = true
}
}
}
func (ccc *lbCacheClientConn) UpdateBalancerState(s connectivity.State, p balancer.Picker) {
ccc.cc.UpdateBalancerState(s, p)
}
func (ccc *lbCacheClientConn) close() {
ccc.mu.Lock()
// Only cancel all existing timers. There's no need to remove SubConns.
for _, entry := range ccc.subConnCache {
entry.cancel()
}
ccc.mu.Unlock()
}

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