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singleton.go
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singleton.go
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/*
*
* Copyright 2020 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 xdsclient
import (
"fmt"
"sync"
"time"
"google.golang.org/grpc/xds/internal/xdsclient/bootstrap"
)
const (
defaultWatchExpiryTimeout = 15 * time.Second
defaultIdleAuthorityDeleteTimeout = 5 * time.Minute
)
var (
// This is the client returned by New(). It contains one client implementation,
// and maintains the refcount.
singletonClient = &clientRefCounted{}
// The following functions are no-ops in the actual code, but can be
// overridden in tests to give them visibility into certain events.
singletonClientImplCreateHook = func() {}
singletonClientImplCloseHook = func() {}
)
// To override in tests.
var bootstrapNewConfig = bootstrap.NewConfig
// onceClosingClient is a thin wrapper around clientRefCounted. The Close()
// method is overridden such that the underlying reference counted client's
// Close() is called at most once, thereby making Close() idempotent.
//
// This is the type which is returned by New() and NewWithConfig(), making it
// safe for these callers to call Close() any number of times.
type onceClosingClient struct {
XDSClient
once sync.Once
}
func (o *onceClosingClient) Close() {
o.once.Do(o.XDSClient.Close)
}
func newRefCountedWithConfig(config *bootstrap.Config) (XDSClient, error) {
singletonClient.mu.Lock()
defer singletonClient.mu.Unlock()
// If the client implementation was created, increment ref count and return
// the client.
if singletonClient.clientImpl != nil {
singletonClient.refCount++
return &onceClosingClient{XDSClient: singletonClient}, nil
}
// If the passed in config is nil, perform bootstrap to read config.
if config == nil {
var err error
config, err = bootstrapNewConfig()
if err != nil {
return nil, fmt.Errorf("xds: failed to read bootstrap file: %v", err)
}
}
// Create the new client implementation.
c, err := newWithConfig(config, defaultWatchExpiryTimeout, defaultIdleAuthorityDeleteTimeout)
if err != nil {
return nil, err
}
singletonClient.clientImpl = c
singletonClient.refCount++
singletonClientImplCreateHook()
logger.Info("xDS bootstrap: %s", c.BootstrapConfig().XDSServer.NodeProto.String())
return &onceClosingClient{XDSClient: singletonClient}, nil
}
// clientRefCounted is ref-counted, and to be shared by the xds resolver and
// balancer implementations, across multiple ClientConns and Servers.
type clientRefCounted struct {
*clientImpl
// This mu protects all the fields, including the embedded clientImpl above.
mu sync.Mutex
refCount int
}
// Close closes the client. It does ref count of the xds client implementation,
// and closes the gRPC connection to the management server when ref count
// reaches 0.
func (c *clientRefCounted) Close() {
c.mu.Lock()
defer c.mu.Unlock()
c.refCount--
if c.refCount == 0 {
c.clientImpl.Close()
// Set clientImpl back to nil. So if New() is called after this, a new
// implementation will be created.
c.clientImpl = nil
singletonClientImplCloseHook()
}
}