orca: create ORCA producer for LB policies to use to receive OOB load reports

balancer/balancer.go

@@ -110,6 +110,11 @@ type SubConn interface {
 	UpdateAddresses([]resolver.Address)
 	// Connect starts the connecting for this SubConn.
 	Connect()
+	// GetOrBuildProducer returns a reference to the existing Producer for this
+	// ProducerBuilder in this SubConn, or, if one does not currently exist,
+	// creates a new one and returns it.  Returns a close function which must
+	// be called when the Producer is no longer needed.
+	GetOrBuildProducer(ProducerBuilder) (p Producer, close func())
 }
 
 // NewSubConnOptions contains options to create new SubConn.
@@ -371,3 +376,21 @@ type ClientConnState struct {
 // ErrBadResolverState may be returned by UpdateClientConnState to indicate a
 // problem with the provided name resolver data.
 var ErrBadResolverState = errors.New("bad resolver state")
+
+// A ProducerBuilder is a simple constructor for a Producer.  It is used by the
+// SubConn to create producers when needed.
+type ProducerBuilder interface {
+	// Build creates a Producer.  The first parameter is always a
+	// grpc.ClientConnInterface (a type to allow creating RPCs/streams on the
+	// associated SubConn), but is declared as interface{} to avoid a
+	// dependency cycle.  Should also return a close function that will be
+	// called when all references to the Producer have been given up.
+	Build(grpcClientConnInterface interface{}) (p Producer, close func())
+}
+
+// A Producer is a type shared among potentially many consumers.  It is
+// associated with a SubConn, and an implementation will typically contain
+// other methods to provide additional functionality, e.g. configuration or
+// subscription registration.
+type Producer interface {
+}

balancer/base/balancer_test.go

@@ -44,6 +44,10 @@ func (sc *testSubConn) UpdateAddresses(addresses []resolver.Address) {}
 
 func (sc *testSubConn) Connect() {}
 
+func (sc *testSubConn) GetOrBuildProducer(balancer.ProducerBuilder) (balancer.Producer, func()) {
+	return nil, nil
+}
+
 // testPickBuilder creates balancer.Picker for test.
 type testPickBuilder struct {
 	validate func(info PickerBuildInfo)

balancer_conn_wrappers.go

@@ -19,17 +19,20 @@
 package grpc
 
 import (
+	"context"
 	"fmt"
 	"strings"
 	"sync"
 
 	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/internal/balancer/gracefulswitch"
 	"google.golang.org/grpc/internal/buffer"
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/internal/grpcsync"
 	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/status"
 )
 
 // ccBalancerWrapper sits between the ClientConn and the Balancer.
@@ -305,7 +308,7 @@ func (ccb *ccBalancerWrapper) NewSubConn(addrs []resolver.Address, opts balancer
 		channelz.Warningf(logger, ccb.cc.channelzID, "acBalancerWrapper: NewSubConn: failed to newAddrConn: %v", err)
 		return nil, err
 	}
-	acbw := &acBalancerWrapper{ac: ac}
+	acbw := &acBalancerWrapper{ac: ac, producers: make(map[balancer.ProducerBuilder]*refCountedProducer)}
 	acbw.ac.mu.Lock()
 	ac.acbw = acbw
 	acbw.ac.mu.Unlock()
@@ -359,8 +362,9 @@ func (ccb *ccBalancerWrapper) Target() string {
 // acBalancerWrapper is a wrapper on top of ac for balancers.
 // It implements balancer.SubConn interface.
 type acBalancerWrapper struct {
-	mu sync.Mutex
-	ac *addrConn
+	mu        sync.Mutex
+	ac        *addrConn
+	producers map[balancer.ProducerBuilder]*refCountedProducer
 }
 
 func (acbw *acBalancerWrapper) UpdateAddresses(addrs []resolver.Address) {
@@ -414,3 +418,64 @@ func (acbw *acBalancerWrapper) getAddrConn() *addrConn {
 	defer acbw.mu.Unlock()
 	return acbw.ac
 }
+
+var errSubConnNotReady = status.Error(codes.Unavailable, "SubConn not currently connected")
+
+// NewStream begins a streaming RPC on the addrConn.  If the addrConn is not
+// ready, returns errSubConnNotReady.
+func (acbw *acBalancerWrapper) NewStream(ctx context.Context, desc *StreamDesc, method string, opts ...CallOption) (ClientStream, error) {
+	transport := acbw.ac.getReadyTransport()
+	if transport == nil {
+		return nil, errSubConnNotReady
+	}
+	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)
+}

internal/grpcsync/oncefunc.go

@@ -0,0 +1,32 @@
+/*
+ *
+ * Copyright 2022 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 grpcsync
+
+import (
+	"sync"
+)
+
+// OnceFunc returns a function wrapping f which ensures f is only executed
+// once even if the returned function is executed multiple times.
+func OnceFunc(f func()) func() {
+	var once sync.Once
+	return func() {
+		once.Do(f)
+	}
+}

internal/testutils/balancer.go

@@ -68,6 +68,11 @@ func (tsc *TestSubConn) Connect() {
 	}
 }
 
+// GetOrBuildProducer is a no-op.
+func (tsc *TestSubConn) GetOrBuildProducer(balancer.ProducerBuilder) (balancer.Producer, func()) {
+	return nil, nil
+}
+
 // String implements stringer to print human friendly error message.
 func (tsc *TestSubConn) String() string {
 	return tsc.id

orca/internal/internal.go

@@ -20,8 +20,15 @@
 // avoid polluting the godoc of the top-level orca package.
 package internal
 
+import ibackoff "google.golang.org/grpc/internal/backoff"
+
 // AllowAnyMinReportingInterval prevents clamping of the MinReportingInterval
 // configured via ServiceOptions, to a minimum of 30s.
 //
 // For testing purposes only.
 var AllowAnyMinReportingInterval interface{} // func(*ServiceOptions)
+
+// DefaultBackoffFunc is used by the producer to control its backoff behavior.
+//
+// For testing purposes only.
+var DefaultBackoffFunc = ibackoff.DefaultExponential.Backoff