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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"
"io"
"sync"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/internal/channelz"
"google.golang.org/grpc/internal/transport"
"google.golang.org/grpc/status"
)
// pickerWrapper is a wrapper of balancer.Picker. It blocks on certain pick
// actions and unblock when there's a picker update.
type pickerWrapper struct {
mu sync.Mutex
done bool
blockingCh chan struct{}
picker balancer.Picker
}
func newPickerWrapper() *pickerWrapper {
return &pickerWrapper{blockingCh: make(chan struct{})}
}
// updatePicker is called by UpdateBalancerState. It unblocks all blocked pick.
func (pw *pickerWrapper) updatePicker(p balancer.Picker) {
pw.mu.Lock()
if pw.done {
pw.mu.Unlock()
return
}
pw.picker = p
// pw.blockingCh should never be nil.
close(pw.blockingCh)
pw.blockingCh = make(chan struct{})
pw.mu.Unlock()
}
func doneChannelzWrapper(acw *acBalancerWrapper, done func(balancer.DoneInfo)) func(balancer.DoneInfo) {
acw.mu.Lock()
ac := acw.ac
acw.mu.Unlock()
ac.incrCallsStarted()
return func(b balancer.DoneInfo) {
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, func(balancer.DoneInfo), error) {
var ch chan struct{}
var lastPickErr error
for {
pw.mu.Lock()
if pw.done {
pw.mu.Unlock()
return nil, nil, ErrClientConnClosing
}
if pw.picker == nil {
ch = pw.blockingCh
}
if ch == pw.blockingCh {
// This could happen when either:
// - pw.picker is nil (the previous if condition), or
// - has called pick on the current picker.
pw.mu.Unlock()
select {
case <-ctx.Done():
var errStr string
if lastPickErr != nil {
errStr = "latest balancer error: " + lastPickErr.Error()
} else {
errStr = ctx.Err().Error()
}
switch ctx.Err() {
case context.DeadlineExceeded:
return nil, nil, status.Error(codes.DeadlineExceeded, errStr)
case context.Canceled:
return nil, nil, status.Error(codes.Canceled, errStr)
}
case <-ch:
}
continue
}
ch = pw.blockingCh
p := pw.picker
pw.mu.Unlock()
pickResult, err := p.Pick(info)
if err != nil {
if err == balancer.ErrNoSubConnAvailable {
continue
}
if _, ok := status.FromError(err); ok {
// Status error: end the RPC unconditionally with this status.
return nil, nil, dropError{error: err}
}
// For all other errors, wait for ready RPCs should block and other
// RPCs should fail with unavailable.
if !failfast {
lastPickErr = err
continue
}
return nil, nil, status.Error(codes.Unavailable, err.Error())
}
acw, ok := pickResult.SubConn.(*acBalancerWrapper)
if !ok {
logger.Errorf("subconn returned from pick is type %T, not *acBalancerWrapper", pickResult.SubConn)
continue
}
if t := acw.getAddrConn().getReadyTransport(); t != nil {
if channelz.IsOn() {
return t, doneChannelzWrapper(acw, pickResult.Done), nil
}
return t, pickResult.Done, nil
}
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() {
pw.mu.Lock()
defer pw.mu.Unlock()
if pw.done {
return
}
pw.done = true
close(pw.blockingCh)
}
// dropError is a wrapper error that indicates the LB policy wishes to drop the
// RPC and not retry it.
type dropError struct {
error
}
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