gotosocial/vendor/google.golang.org/grpc/balancer_wrapper.go

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/*
*
* 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"
)
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// 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 in order by performing them in the serializer, without
// any mutexes held.
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//
// 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
serializer *grpcsync.CallbackSerializer
serializerCancel context.CancelFunc
// The following fields are only accessed within the serializer or during
// initialization.
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curBalancerName string
balancer *gracefulswitch.Balancer
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// The following field is protected by mu. Caller must take cc.mu before
// taking mu.
mu sync.Mutex
closed bool
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}
// newCCBalancerWrapper creates a new balancer wrapper in idle state. The
// underlying balancer is not created until the switchTo() method is invoked.
func newCCBalancerWrapper(cc *ClientConn) *ccBalancerWrapper {
ctx, cancel := context.WithCancel(cc.ctx)
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ccb := &ccBalancerWrapper{
cc: cc,
opts: balancer.BuildOptions{
DialCreds: cc.dopts.copts.TransportCredentials,
CredsBundle: cc.dopts.copts.CredsBundle,
Dialer: cc.dopts.copts.Dialer,
Authority: cc.authority,
CustomUserAgent: cc.dopts.copts.UserAgent,
ChannelzParentID: cc.channelzID,
Target: cc.parsedTarget,
},
serializer: grpcsync.NewCallbackSerializer(ctx),
serializerCancel: cancel,
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}
ccb.balancer = gracefulswitch.NewBalancer(ccb, ccb.opts)
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return ccb
}
// updateClientConnState is invoked by grpc to push a ClientConnState update to
// the underlying balancer. This is always executed from the serializer, so
// it is safe to call into the balancer here.
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func (ccb *ccBalancerWrapper) updateClientConnState(ccs *balancer.ClientConnState) error {
errCh := make(chan error)
ok := ccb.serializer.Schedule(func(ctx context.Context) {
defer close(errCh)
if ctx.Err() != nil || ccb.balancer == nil {
return
}
err := ccb.balancer.UpdateClientConnState(*ccs)
if logger.V(2) && err != nil {
logger.Infof("error from balancer.UpdateClientConnState: %v", err)
}
errCh <- err
})
if !ok {
return nil
}
return <-errCh
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}
// resolverError is invoked by grpc to push a resolver error to the underlying
// balancer. The call to the balancer is executed from the serializer.
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func (ccb *ccBalancerWrapper) resolverError(err error) {
ccb.serializer.Schedule(func(ctx context.Context) {
if ctx.Err() != nil || ccb.balancer == nil {
return
}
ccb.balancer.ResolverError(err)
})
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}
// 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.serializer.Schedule(func(ctx context.Context) {
if ctx.Err() != nil || ccb.balancer == nil {
return
}
// 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)
})
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}
// 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) {
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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()
}
// close initiates async shutdown of the wrapper. cc.mu must be held when
// calling this function. To determine the wrapper has finished shutting down,
// the channel should block on ccb.serializer.Done() without cc.mu held.
func (ccb *ccBalancerWrapper) close() {
ccb.mu.Lock()
ccb.closed = true
ccb.mu.Unlock()
channelz.Info(logger, ccb.cc.channelzID, "ccBalancerWrapper: closing")
ccb.serializer.Schedule(func(context.Context) {
if ccb.balancer == nil {
return
}
ccb.balancer.Close()
ccb.balancer = nil
})
ccb.serializerCancel()
}
// exitIdle invokes the balancer's exitIdle method in the serializer.
func (ccb *ccBalancerWrapper) exitIdle() {
ccb.serializer.Schedule(func(ctx context.Context) {
if ctx.Err() != nil || ccb.balancer == nil {
return
}
ccb.balancer.ExitIdle()
})
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}
func (ccb *ccBalancerWrapper) NewSubConn(addrs []resolver.Address, opts balancer.NewSubConnOptions) (balancer.SubConn, error) {
ccb.cc.mu.Lock()
defer ccb.cc.mu.Unlock()
ccb.mu.Lock()
if ccb.closed {
ccb.mu.Unlock()
return nil, fmt.Errorf("balancer is being closed; no new SubConns allowed")
}
ccb.mu.Unlock()
if len(addrs) == 0 {
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return nil, fmt.Errorf("grpc: cannot create SubConn with empty address list")
}
ac, err := ccb.cc.newAddrConnLocked(addrs, opts)
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if err != nil {
channelz.Warningf(logger, ccb.cc.channelzID, "acBalancerWrapper: NewSubConn: failed to newAddrConn: %v", err)
return nil, err
}
acbw := &acBalancerWrapper{
ccb: ccb,
ac: ac,
producers: make(map[balancer.ProducerBuilder]*refCountedProducer),
stateListener: opts.StateListener,
}
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ac.acbw = acbw
return acbw, nil
}
func (ccb *ccBalancerWrapper) RemoveSubConn(sc balancer.SubConn) {
// The graceful switch balancer will never call this.
logger.Errorf("ccb RemoveSubConn(%v) called unexpectedly, sc")
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}
func (ccb *ccBalancerWrapper) UpdateAddresses(sc balancer.SubConn, addrs []resolver.Address) {
acbw, ok := sc.(*acBalancerWrapper)
if !ok {
return
}
acbw.UpdateAddresses(addrs)
}
func (ccb *ccBalancerWrapper) UpdateState(s balancer.State) {
ccb.cc.mu.Lock()
defer ccb.cc.mu.Unlock()
ccb.mu.Lock()
if ccb.closed {
ccb.mu.Unlock()
return
}
ccb.mu.Unlock()
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// 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.
// Note that there is no need to check if the balancer wrapper was closed,
// as we know the graceful switch LB policy will not call cc if it has been
// closed.
ccb.cc.pickerWrapper.updatePicker(s.Picker)
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ccb.cc.csMgr.updateState(s.ConnectivityState)
}
func (ccb *ccBalancerWrapper) ResolveNow(o resolver.ResolveNowOptions) {
ccb.cc.mu.RLock()
defer ccb.cc.mu.RUnlock()
ccb.mu.Lock()
if ccb.closed {
ccb.mu.Unlock()
return
}
ccb.mu.Unlock()
ccb.cc.resolveNowLocked(o)
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}
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
ccb *ccBalancerWrapper // read-only
stateListener func(balancer.SubConnState)
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mu sync.Mutex
producers map[balancer.ProducerBuilder]*refCountedProducer
}
// updateState is invoked by grpc to push a subConn state update to the
// underlying balancer.
func (acbw *acBalancerWrapper) updateState(s connectivity.State, err error) {
acbw.ccb.serializer.Schedule(func(ctx context.Context) {
if ctx.Err() != nil || acbw.ccb.balancer == nil {
return
}
// Even though it is optional for balancers, gracefulswitch ensures
// opts.StateListener is set, so this cannot ever be nil.
// TODO: delete this comment when UpdateSubConnState is removed.
acbw.stateListener(balancer.SubConnState{ConnectivityState: s, ConnectionError: err})
})
}
func (acbw *acBalancerWrapper) String() string {
return fmt.Sprintf("SubConn(id:%d)", acbw.ac.channelzID.Int())
}
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func (acbw *acBalancerWrapper) UpdateAddresses(addrs []resolver.Address) {
acbw.ac.updateAddrs(addrs)
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}
func (acbw *acBalancerWrapper) Connect() {
go acbw.ac.connect()
}
func (acbw *acBalancerWrapper) Shutdown() {
acbw.ccb.cc.removeAddrConn(acbw.ac, errConnDrain)
}
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// 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.
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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
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}
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 any, reply any, opts ...CallOption) error {
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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)
}