pickfirst: New pick first policy for dualstack

.github/workflows/coverage.yml

@@ -19,6 +19,9 @@ jobs:
       - name: Run coverage
         run: go test -coverprofile=coverage.out -coverpkg=./... ./...
 
+      - name: Run coverage with new pickfirst
+        run: GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=true go test -coverprofile=coverage_new_pickfirst.out -coverpkg=./... ./...
+
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v4
         with:

.github/workflows/testing.yml

@@ -66,6 +66,11 @@ jobs:
           - type: tests
             goversion: '1.21'
 
+          - type: tests
+            goversion: '1.22'
+            testflags: -race
+            grpcenv: 'GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST=true'
+
     steps:
       # Setup the environment.
       - name: Setup GOARCH
@@ -81,7 +86,7 @@ jobs:
       - name: Setup GRPC environment
         if: matrix.grpcenv != ''
         run: echo "${{ matrix.grpcenv }}" >> $GITHUB_ENV
-        
+
       - name: Checkout repo
         uses: actions/checkout@v4
 

balancer/pickfirst/pickfirst.go

@@ -29,13 +29,19 @@ import (
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/grpclog"
 	"google.golang.org/grpc/internal"
+	"google.golang.org/grpc/internal/envconfig"
 	internalgrpclog "google.golang.org/grpc/internal/grpclog"
 	"google.golang.org/grpc/internal/pretty"
 	"google.golang.org/grpc/resolver"
 	"google.golang.org/grpc/serviceconfig"
+
+	_ "google.golang.org/grpc/balancer/pickfirstleaf" // For automatically registering the new pickfirst if required.
 )
 
 func init() {
+	if envconfig.NewPickFirstEnabled {
+		return
+	}
 	balancer.Register(pickfirstBuilder{})
 	internal.ShuffleAddressListForTesting = func(n int, swap func(i, j int)) { rand.Shuffle(n, swap) }
 }