peridot/vendor/google.golang.org/grpc/picker_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"
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"io"
"sync/atomic"
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"google.golang.org/grpc/balancer"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/internal/channelz"
istatus "google.golang.org/grpc/internal/status"
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"google.golang.org/grpc/internal/transport"
"google.golang.org/grpc/stats"
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"google.golang.org/grpc/status"
)
// pickerGeneration stores a picker and a channel used to signal that a picker
// newer than this one is available.
type pickerGeneration struct {
// picker is the picker produced by the LB policy. May be nil if a picker
// has never been produced.
picker balancer.Picker
// blockingCh is closed when the picker has been invalidated because there
// is a new one available.
blockingCh chan struct{}
}
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// pickerWrapper is a wrapper of balancer.Picker. It blocks on certain pick
// actions and unblock when there's a picker update.
type pickerWrapper struct {
// If pickerGen holds a nil pointer, the pickerWrapper is closed.
pickerGen atomic.Pointer[pickerGeneration]
statsHandlers []stats.Handler // to record blocking picker calls
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}
func newPickerWrapper(statsHandlers []stats.Handler) *pickerWrapper {
pw := &pickerWrapper{
statsHandlers: statsHandlers,
}
pw.pickerGen.Store(&pickerGeneration{
blockingCh: make(chan struct{}),
})
return pw
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}
// updatePicker is called by UpdateState calls from the LB policy. It
// unblocks all blocked pick.
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func (pw *pickerWrapper) updatePicker(p balancer.Picker) {
old := pw.pickerGen.Swap(&pickerGeneration{
picker: p,
blockingCh: make(chan struct{}),
})
close(old.blockingCh)
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}
// doneChannelzWrapper performs the following:
// - increments the calls started channelz counter
// - wraps the done function in the passed in result to increment the calls
// failed or calls succeeded channelz counter before invoking the actual
// done function.
func doneChannelzWrapper(acbw *acBalancerWrapper, result *balancer.PickResult) {
ac := acbw.ac
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ac.incrCallsStarted()
done := result.Done
result.Done = func(b balancer.DoneInfo) {
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if b.Err != nil && b.Err != io.EOF {
ac.incrCallsFailed()
} else {
ac.incrCallsSucceeded()
}
if done != nil {
done(b)
}
}
}
// pick returns the transport that will be used for the RPC.
// It may block in the following cases:
// - there's no picker
// - the current picker returns ErrNoSubConnAvailable
// - the current picker returns other errors and failfast is false.
// - the subConn returned by the current picker is not READY
// When one of these situations happens, pick blocks until the picker gets updated.
func (pw *pickerWrapper) pick(ctx context.Context, failfast bool, info balancer.PickInfo) (transport.ClientTransport, balancer.PickResult, error) {
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var ch chan struct{}
var lastPickErr error
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for {
pg := pw.pickerGen.Load()
if pg == nil {
return nil, balancer.PickResult{}, ErrClientConnClosing
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}
if pg.picker == nil {
ch = pg.blockingCh
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}
if ch == pg.blockingCh {
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// This could happen when either:
// - pw.picker is nil (the previous if condition), or
// - we have already called pick on the current picker.
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select {
case <-ctx.Done():
var errStr string
if lastPickErr != nil {
errStr = "latest balancer error: " + lastPickErr.Error()
} else {
errStr = fmt.Sprintf("received context error while waiting for new LB policy update: %s", ctx.Err().Error())
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}
switch ctx.Err() {
case context.DeadlineExceeded:
return nil, balancer.PickResult{}, status.Error(codes.DeadlineExceeded, errStr)
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case context.Canceled:
return nil, balancer.PickResult{}, status.Error(codes.Canceled, errStr)
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}
case <-ch:
}
continue
}
// If the channel is set, it means that the pick call had to wait for a
// new picker at some point. Either it's the first iteration and this
// function received the first picker, or a picker errored with
// ErrNoSubConnAvailable or errored with failfast set to false, which
// will trigger a continue to the next iteration. In the first case this
// conditional will hit if this call had to block (the channel is set).
// In the second case, the only way it will get to this conditional is
// if there is a new picker.
if ch != nil {
for _, sh := range pw.statsHandlers {
sh.HandleRPC(ctx, &stats.PickerUpdated{})
}
}
ch = pg.blockingCh
p := pg.picker
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pickResult, err := p.Pick(info)
if err != nil {
if err == balancer.ErrNoSubConnAvailable {
continue
}
if st, ok := status.FromError(err); ok {
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// Status error: end the RPC unconditionally with this status.
// First restrict the code to the list allowed by gRFC A54.
if istatus.IsRestrictedControlPlaneCode(st) {
err = status.Errorf(codes.Internal, "received picker error with illegal status: %v", err)
}
return nil, balancer.PickResult{}, dropError{error: err}
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}
// For all other errors, wait for ready RPCs should block and other
// RPCs should fail with unavailable.
if !failfast {
lastPickErr = err
continue
}
return nil, balancer.PickResult{}, status.Error(codes.Unavailable, err.Error())
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}
acbw, ok := pickResult.SubConn.(*acBalancerWrapper)
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if !ok {
logger.Errorf("subconn returned from pick is type %T, not *acBalancerWrapper", pickResult.SubConn)
continue
}
if t := acbw.ac.getReadyTransport(); t != nil {
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if channelz.IsOn() {
doneChannelzWrapper(acbw, &pickResult)
return t, pickResult, nil
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}
return t, pickResult, nil
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}
if pickResult.Done != nil {
// Calling done with nil error, no bytes sent and no bytes received.
// DoneInfo with default value works.
pickResult.Done(balancer.DoneInfo{})
}
logger.Infof("blockingPicker: the picked transport is not ready, loop back to repick")
// If ok == false, ac.state is not READY.
// A valid picker always returns READY subConn. This means the state of ac
// just changed, and picker will be updated shortly.
// continue back to the beginning of the for loop to repick.
}
}
func (pw *pickerWrapper) close() {
old := pw.pickerGen.Swap(nil)
close(old.blockingCh)
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}
// reset clears the pickerWrapper and prepares it for being used again when idle
// mode is exited.
func (pw *pickerWrapper) reset() {
old := pw.pickerGen.Swap(&pickerGeneration{blockingCh: make(chan struct{})})
close(old.blockingCh)
}
// dropError is a wrapper error that indicates the LB policy wishes to drop the
// RPC and not retry it.
type dropError struct {
error
}