ARO-RP/vendor/google.golang.org/grpc/balancer_conn_wrappers.go

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Go

/*
*
* Copyright 2017 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 grpc
import (
"context"
"fmt"
"strings"
"sync"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/connectivity"
"google.golang.org/grpc/internal/balancer/gracefulswitch"
"google.golang.org/grpc/internal/channelz"
"google.golang.org/grpc/internal/grpcsync"
"google.golang.org/grpc/resolver"
)
type ccbMode int
const (
ccbModeActive = iota
ccbModeIdle
ccbModeClosed
ccbModeExitingIdle
)
// ccBalancerWrapper sits between the ClientConn and the Balancer.
//
// ccBalancerWrapper implements methods corresponding to the ones on the
// balancer.Balancer interface. The ClientConn is free to call these methods
// concurrently and the ccBalancerWrapper ensures that calls from the ClientConn
// to the Balancer happen synchronously and in order.
//
// ccBalancerWrapper also implements the balancer.ClientConn interface and is
// passed to the Balancer implementations. It invokes unexported methods on the
// ClientConn to handle these calls from the Balancer.
//
// It uses the gracefulswitch.Balancer internally to ensure that balancer
// switches happen in a graceful manner.
type ccBalancerWrapper struct {
// The following fields are initialized when the wrapper is created and are
// read-only afterwards, and therefore can be accessed without a mutex.
cc *ClientConn
opts balancer.BuildOptions
// Outgoing (gRPC --> balancer) calls are guaranteed to execute in a
// mutually exclusive manner as they are scheduled in the serializer. Fields
// accessed *only* in these serializer callbacks, can therefore be accessed
// without a mutex.
balancer *gracefulswitch.Balancer
curBalancerName string
// mu guards access to the below fields. Access to the serializer and its
// cancel function needs to be mutex protected because they are overwritten
// when the wrapper exits idle mode.
mu sync.Mutex
serializer *grpcsync.CallbackSerializer // To serialize all outoing calls.
serializerCancel context.CancelFunc // To close the seralizer at close/enterIdle time.
mode ccbMode // Tracks the current mode of the wrapper.
}
// newCCBalancerWrapper creates a new balancer wrapper. The underlying balancer
// is not created until the switchTo() method is invoked.
func newCCBalancerWrapper(cc *ClientConn, bopts balancer.BuildOptions) *ccBalancerWrapper {
ctx, cancel := context.WithCancel(context.Background())
ccb := &ccBalancerWrapper{
cc: cc,
opts: bopts,
serializer: grpcsync.NewCallbackSerializer(ctx),
serializerCancel: cancel,
}
ccb.balancer = gracefulswitch.NewBalancer(ccb, bopts)
return ccb
}
// updateClientConnState is invoked by grpc to push a ClientConnState update to
// the underlying balancer.
func (ccb *ccBalancerWrapper) updateClientConnState(ccs *balancer.ClientConnState) error {
ccb.mu.Lock()
errCh := make(chan error, 1)
// Here and everywhere else where Schedule() is called, it is done with the
// lock held. But the lock guards only the scheduling part. The actual
// callback is called asynchronously without the lock being held.
ok := ccb.serializer.Schedule(func(_ context.Context) {
// If the addresses specified in the update contain addresses of type
// "grpclb" and the selected LB policy is not "grpclb", these addresses
// will be filtered out and ccs will be modified with the updated
// address list.
if ccb.curBalancerName != grpclbName {
var addrs []resolver.Address
for _, addr := range ccs.ResolverState.Addresses {
if addr.Type == resolver.GRPCLB {
continue
}
addrs = append(addrs, addr)
}
ccs.ResolverState.Addresses = addrs
}
errCh <- ccb.balancer.UpdateClientConnState(*ccs)
})
if !ok {
// If we are unable to schedule a function with the serializer, it
// indicates that it has been closed. A serializer is only closed when
// the wrapper is closed or is in idle.
ccb.mu.Unlock()
return fmt.Errorf("grpc: cannot send state update to a closed or idle balancer")
}
ccb.mu.Unlock()
// We get here only if the above call to Schedule succeeds, in which case it
// is guaranteed that the scheduled function will run. Therefore it is safe
// to block on this channel.
err := <-errCh
if logger.V(2) && err != nil {
logger.Infof("error from balancer.UpdateClientConnState: %v", err)
}
return err
}
// updateSubConnState is invoked by grpc to push a subConn state update to the
// underlying balancer.
func (ccb *ccBalancerWrapper) updateSubConnState(sc balancer.SubConn, s connectivity.State, err error) {
ccb.mu.Lock()
ccb.serializer.Schedule(func(_ context.Context) {
ccb.balancer.UpdateSubConnState(sc, balancer.SubConnState{ConnectivityState: s, ConnectionError: err})
})
ccb.mu.Unlock()
}
func (ccb *ccBalancerWrapper) resolverError(err error) {
ccb.mu.Lock()
ccb.serializer.Schedule(func(_ context.Context) {
ccb.balancer.ResolverError(err)
})
ccb.mu.Unlock()
}
// switchTo is invoked by grpc to instruct the balancer wrapper to switch to the
// LB policy identified by name.
//
// ClientConn calls newCCBalancerWrapper() at creation time. Upon receipt of the
// first good update from the name resolver, it determines the LB policy to use
// and invokes the switchTo() method. Upon receipt of every subsequent update
// from the name resolver, it invokes this method.
//
// the ccBalancerWrapper keeps track of the current LB policy name, and skips
// the graceful balancer switching process if the name does not change.
func (ccb *ccBalancerWrapper) switchTo(name string) {
ccb.mu.Lock()
ccb.serializer.Schedule(func(_ context.Context) {
// TODO: Other languages use case-sensitive balancer registries. We should
// switch as well. See: https://github.com/grpc/grpc-go/issues/5288.
if strings.EqualFold(ccb.curBalancerName, name) {
return
}
ccb.buildLoadBalancingPolicy(name)
})
ccb.mu.Unlock()
}
// buildLoadBalancingPolicy performs the following:
// - retrieve a balancer builder for the given name. Use the default LB
// policy, pick_first, if no LB policy with name is found in the registry.
// - instruct the gracefulswitch balancer to switch to the above builder. This
// will actually build the new balancer.
// - update the `curBalancerName` field
//
// Must be called from a serializer callback.
func (ccb *ccBalancerWrapper) buildLoadBalancingPolicy(name string) {
builder := balancer.Get(name)
if builder == nil {
channelz.Warningf(logger, ccb.cc.channelzID, "Channel switches to new LB policy %q, since the specified LB policy %q was not registered", PickFirstBalancerName, name)
builder = newPickfirstBuilder()
} else {
channelz.Infof(logger, ccb.cc.channelzID, "Channel switches to new LB policy %q", name)
}
if err := ccb.balancer.SwitchTo(builder); err != nil {
channelz.Errorf(logger, ccb.cc.channelzID, "Channel failed to build new LB policy %q: %v", name, err)
return
}
ccb.curBalancerName = builder.Name()
}
func (ccb *ccBalancerWrapper) close() {
channelz.Info(logger, ccb.cc.channelzID, "ccBalancerWrapper: closing")
ccb.closeBalancer(ccbModeClosed)
}
// enterIdleMode is invoked by grpc when the channel enters idle mode upon
// expiry of idle_timeout. This call blocks until the balancer is closed.
func (ccb *ccBalancerWrapper) enterIdleMode() {
channelz.Info(logger, ccb.cc.channelzID, "ccBalancerWrapper: entering idle mode")
ccb.closeBalancer(ccbModeIdle)
}
// closeBalancer is invoked when the channel is being closed or when it enters
// idle mode upon expiry of idle_timeout.
func (ccb *ccBalancerWrapper) closeBalancer(m ccbMode) {
ccb.mu.Lock()
if ccb.mode == ccbModeClosed || ccb.mode == ccbModeIdle {
ccb.mu.Unlock()
return
}
ccb.mode = m
done := ccb.serializer.Done
b := ccb.balancer
ok := ccb.serializer.Schedule(func(_ context.Context) {
// Close the serializer to ensure that no more calls from gRPC are sent
// to the balancer.
ccb.serializerCancel()
// Empty the current balancer name because we don't have a balancer
// anymore and also so that we act on the next call to switchTo by
// creating a new balancer specified by the new resolver.
ccb.curBalancerName = ""
})
if !ok {
ccb.mu.Unlock()
return
}
ccb.mu.Unlock()
// Give enqueued callbacks a chance to finish.
<-done
// Spawn a goroutine to close the balancer (since it may block trying to
// cleanup all allocated resources) and return early.
go b.Close()
}
// exitIdleMode is invoked by grpc when the channel exits idle mode either
// because of an RPC or because of an invocation of the Connect() API. This
// recreates the balancer that was closed previously when entering idle mode.
//
// If the channel is not in idle mode, we know for a fact that we are here as a
// result of the user calling the Connect() method on the ClientConn. In this
// case, we can simply forward the call to the underlying balancer, instructing
// it to reconnect to the backends.
func (ccb *ccBalancerWrapper) exitIdleMode() {
ccb.mu.Lock()
if ccb.mode == ccbModeClosed {
// Request to exit idle is a no-op when wrapper is already closed.
ccb.mu.Unlock()
return
}
if ccb.mode == ccbModeIdle {
// Recreate the serializer which was closed when we entered idle.
ctx, cancel := context.WithCancel(context.Background())
ccb.serializer = grpcsync.NewCallbackSerializer(ctx)
ccb.serializerCancel = cancel
}
// The ClientConn guarantees that mutual exclusion between close() and
// exitIdleMode(), and since we just created a new serializer, we can be
// sure that the below function will be scheduled.
done := make(chan struct{})
ccb.serializer.Schedule(func(_ context.Context) {
defer close(done)
ccb.mu.Lock()
defer ccb.mu.Unlock()
if ccb.mode != ccbModeIdle {
ccb.balancer.ExitIdle()
return
}
// Gracefulswitch balancer does not support a switchTo operation after
// being closed. Hence we need to create a new one here.
ccb.balancer = gracefulswitch.NewBalancer(ccb, ccb.opts)
ccb.mode = ccbModeActive
channelz.Info(logger, ccb.cc.channelzID, "ccBalancerWrapper: exiting idle mode")
})
ccb.mu.Unlock()
<-done
}
func (ccb *ccBalancerWrapper) isIdleOrClosed() bool {
ccb.mu.Lock()
defer ccb.mu.Unlock()
return ccb.mode == ccbModeIdle || ccb.mode == ccbModeClosed
}
func (ccb *ccBalancerWrapper) NewSubConn(addrs []resolver.Address, opts balancer.NewSubConnOptions) (balancer.SubConn, error) {
if ccb.isIdleOrClosed() {
return nil, fmt.Errorf("grpc: cannot create SubConn when balancer is closed or idle")
}
if len(addrs) == 0 {
return nil, fmt.Errorf("grpc: cannot create SubConn with empty address list")
}
ac, err := ccb.cc.newAddrConn(addrs, opts)
if err != nil {
channelz.Warningf(logger, ccb.cc.channelzID, "acBalancerWrapper: NewSubConn: failed to newAddrConn: %v", err)
return nil, err
}
acbw := &acBalancerWrapper{ac: ac, producers: make(map[balancer.ProducerBuilder]*refCountedProducer)}
ac.acbw = acbw
return acbw, nil
}
func (ccb *ccBalancerWrapper) RemoveSubConn(sc balancer.SubConn) {
if ccb.isIdleOrClosed() {
// It it safe to ignore this call when the balancer is closed or in idle
// because the ClientConn takes care of closing the connections.
//
// Not returning early from here when the balancer is closed or in idle
// leads to a deadlock though, because of the following sequence of
// calls when holding cc.mu:
// cc.exitIdleMode --> ccb.enterIdleMode --> gsw.Close -->
// ccb.RemoveAddrConn --> cc.removeAddrConn
return
}
acbw, ok := sc.(*acBalancerWrapper)
if !ok {
return
}
ccb.cc.removeAddrConn(acbw.ac, errConnDrain)
}
func (ccb *ccBalancerWrapper) UpdateAddresses(sc balancer.SubConn, addrs []resolver.Address) {
if ccb.isIdleOrClosed() {
return
}
acbw, ok := sc.(*acBalancerWrapper)
if !ok {
return
}
acbw.UpdateAddresses(addrs)
}
func (ccb *ccBalancerWrapper) UpdateState(s balancer.State) {
if ccb.isIdleOrClosed() {
return
}
// Update picker before updating state. Even though the ordering here does
// not matter, it can lead to multiple calls of Pick in the common start-up
// case where we wait for ready and then perform an RPC. If the picker is
// updated later, we could call the "connecting" picker when the state is
// updated, and then call the "ready" picker after the picker gets updated.
ccb.cc.blockingpicker.updatePicker(s.Picker)
ccb.cc.csMgr.updateState(s.ConnectivityState)
}
func (ccb *ccBalancerWrapper) ResolveNow(o resolver.ResolveNowOptions) {
if ccb.isIdleOrClosed() {
return
}
ccb.cc.resolveNow(o)
}
func (ccb *ccBalancerWrapper) Target() string {
return ccb.cc.target
}
// acBalancerWrapper is a wrapper on top of ac for balancers.
// It implements balancer.SubConn interface.
type acBalancerWrapper struct {
ac *addrConn // read-only
mu sync.Mutex
producers map[balancer.ProducerBuilder]*refCountedProducer
}
func (acbw *acBalancerWrapper) String() string {
return fmt.Sprintf("SubConn(id:%d)", acbw.ac.channelzID.Int())
}
func (acbw *acBalancerWrapper) UpdateAddresses(addrs []resolver.Address) {
acbw.ac.updateAddrs(addrs)
}
func (acbw *acBalancerWrapper) Connect() {
go acbw.ac.connect()
}
// NewStream begins a streaming RPC on the addrConn. If the addrConn is not
// ready, blocks until it is or ctx expires. Returns an error when the context
// expires or the addrConn is shut down.
func (acbw *acBalancerWrapper) NewStream(ctx context.Context, desc *StreamDesc, method string, opts ...CallOption) (ClientStream, error) {
transport, err := acbw.ac.getTransport(ctx)
if err != nil {
return nil, err
}
return newNonRetryClientStream(ctx, desc, method, transport, acbw.ac, opts...)
}
// Invoke performs a unary RPC. If the addrConn is not ready, returns
// errSubConnNotReady.
func (acbw *acBalancerWrapper) Invoke(ctx context.Context, method string, args interface{}, reply interface{}, opts ...CallOption) error {
cs, err := acbw.NewStream(ctx, unaryStreamDesc, method, opts...)
if err != nil {
return err
}
if err := cs.SendMsg(args); err != nil {
return err
}
return cs.RecvMsg(reply)
}
type refCountedProducer struct {
producer balancer.Producer
refs int // number of current refs to the producer
close func() // underlying producer's close function
}
func (acbw *acBalancerWrapper) GetOrBuildProducer(pb balancer.ProducerBuilder) (balancer.Producer, func()) {
acbw.mu.Lock()
defer acbw.mu.Unlock()
// Look up existing producer from this builder.
pData := acbw.producers[pb]
if pData == nil {
// Not found; create a new one and add it to the producers map.
p, close := pb.Build(acbw)
pData = &refCountedProducer{producer: p, close: close}
acbw.producers[pb] = pData
}
// Account for this new reference.
pData.refs++
// Return a cleanup function wrapped in a OnceFunc to remove this reference
// and delete the refCountedProducer from the map if the total reference
// count goes to zero.
unref := func() {
acbw.mu.Lock()
pData.refs--
if pData.refs == 0 {
defer pData.close() // Run outside the acbw mutex
delete(acbw.producers, pb)
}
acbw.mu.Unlock()
}
return pData.producer, grpcsync.OnceFunc(unref)
}