From bd7f82c7b1295ecec7cbec0d4be6c7d1ac470941 Mon Sep 17 00:00:00 2001
From: dfawley <dfawley@google.com>
Date: Tue, 29 May 2018 09:06:35 -0700
Subject: [PATCH] internal/grpcrand: New package for concurrency-safe randoms
 (#2106)

---
 backoff.go                    |  5 ++--
 internal/grpcrand/grpcrand.go | 56 +++++++++++++++++++++++++++++++++++
 resolver/dns/dns_resolver.go  |  5 ++--
 transport/http2_server.go     |  6 ++--
 vet.sh                        |  3 +-
 5 files changed, 65 insertions(+), 10 deletions(-)
 create mode 100644 internal/grpcrand/grpcrand.go

diff --git a/backoff.go b/backoff.go
index c40facce5..2fb322150 100644
--- a/backoff.go
+++ b/backoff.go
@@ -19,8 +19,9 @@
 package grpc
 
 import (
-	"math/rand"
 	"time"
+
+	"google.golang.org/grpc/internal/grpcrand"
 )
 
 // DefaultBackoffConfig uses values specified for backoff in
@@ -88,7 +89,7 @@ func (bc BackoffConfig) backoff(retries int) time.Duration {
 	}
 	// Randomize backoff delays so that if a cluster of requests start at
 	// the same time, they won't operate in lockstep.
-	backoff *= 1 + bc.jitter*(rand.Float64()*2-1)
+	backoff *= 1 + bc.jitter*(grpcrand.Float64()*2-1)
 	if backoff < 0 {
 		return 0
 	}
diff --git a/internal/grpcrand/grpcrand.go b/internal/grpcrand/grpcrand.go
new file mode 100644
index 000000000..200b115ca
--- /dev/null
+++ b/internal/grpcrand/grpcrand.go
@@ -0,0 +1,56 @@
+/*
+ *
+ * Copyright 2018 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 grpcrand implements math/rand functions in a concurrent-safe way
+// with a global random source, independent of math/rand's global source.
+package grpcrand
+
+import (
+	"math/rand"
+	"sync"
+	"time"
+)
+
+var (
+	r  = rand.New(rand.NewSource(time.Now().UnixNano()))
+	mu sync.Mutex
+)
+
+// Int63n implements rand.Int63n on the grpcrand global source.
+func Int63n(n int64) int64 {
+	mu.Lock()
+	res := r.Int63n(n)
+	mu.Unlock()
+	return res
+}
+
+// Intn implements rand.Intn on the grpcrand global source.
+func Intn(n int) int {
+	mu.Lock()
+	res := r.Intn(n)
+	mu.Unlock()
+	return res
+}
+
+// Float64 implements rand.Float64 on the grpcrand global source.
+func Float64() float64 {
+	mu.Lock()
+	res := r.Float64()
+	mu.Unlock()
+	return res
+}
diff --git a/resolver/dns/dns_resolver.go b/resolver/dns/dns_resolver.go
index c1cabfc99..4729ae575 100644
--- a/resolver/dns/dns_resolver.go
+++ b/resolver/dns/dns_resolver.go
@@ -24,7 +24,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"math/rand"
 	"net"
 	"os"
 	"strconv"
@@ -34,6 +33,7 @@ import (
 
 	"golang.org/x/net/context"
 	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal/grpcrand"
 	"google.golang.org/grpc/resolver"
 )
 
@@ -52,7 +52,6 @@ const (
 
 var (
 	errMissingAddr = errors.New("missing address")
-	randomGen      = rand.New(rand.NewSource(time.Now().UnixNano()))
 )
 
 // NewBuilder creates a dnsBuilder which is used to factory DNS resolvers.
@@ -346,7 +345,7 @@ func chosenByPercentage(a *int) bool {
 	if a == nil {
 		return true
 	}
-	return randomGen.Intn(100)+1 <= *a
+	return grpcrand.Intn(100)+1 <= *a
 }
 
 func canaryingSC(js string) string {
diff --git a/transport/http2_server.go b/transport/http2_server.go
index af0095745..8d1fe06bc 100644
--- a/transport/http2_server.go
+++ b/transport/http2_server.go
@@ -24,7 +24,6 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"math/rand"
 	"net"
 	"strconv"
 	"sync"
@@ -39,6 +38,7 @@ import (
 	"google.golang.org/grpc/channelz"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/internal/grpcrand"
 	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/peer"
@@ -1125,14 +1125,12 @@ func (t *http2Server) getOutFlowWindow() int64 {
 	}
 }
 
-var rgen = rand.New(rand.NewSource(time.Now().UnixNano()))
-
 func getJitter(v time.Duration) time.Duration {
 	if v == infinity {
 		return 0
 	}
 	// Generate a jitter between +/- 10% of the value.
 	r := int64(v / 10)
-	j := rgen.Int63n(2*r) - r
+	j := grpcrand.Int63n(2*r) - r
 	return time.Duration(j)
 }
diff --git a/vet.sh b/vet.sh
index 6126ab64b..079bc2896 100755
--- a/vet.sh
+++ b/vet.sh
@@ -54,7 +54,8 @@ if git status --porcelain | read; then
 fi
 
 git ls-files "*.go" | xargs grep -L "\(Copyright [0-9]\{4,\} gRPC authors\)\|DO NOT EDIT" 2>&1 | tee /dev/stderr | (! read)
-git ls-files "*.go" | xargs grep -l "\"unsafe\"" 2>&1 | (! grep -v '_test.go') | tee /dev/stderr | (! read)
+git ls-files "*.go" | xargs grep -l '"unsafe"' 2>&1 | (! grep -v '_test.go') | tee /dev/stderr | (! read)
+git ls-files "*.go" | xargs grep -l '"math/rand"' 2>&1 | (! grep -v '^examples\|^stress\|grpcrand') | tee /dev/stderr | (! read)
 gofmt -s -d -l . 2>&1 | tee /dev/stderr | (! read)
 goimports -l . 2>&1 | tee /dev/stderr | (! read)
 golint ./... 2>&1 | (grep -vE "(_mock|\.pb)\.go:" || true) | tee /dev/stderr | (! read)