From 3b89ac7cf0c818ef5138f88a8131767041c6deff Mon Sep 17 00:00:00 2001
From: Dmitriy Dumanskiy <doom369@gmail.com>
Date: Mon, 19 Apr 2021 14:56:16 +0300
Subject: [PATCH] Use ThreadLocalRandom instead of Math.random() (#11165)

Motivation:

`ThreadLocalRandom` doesn't cause contention. Also `nextInt()` generates only 4 random bytes while `Math.random()` generates 8 bytes.

Modification:

Replaced `(int) Math.random()` with `PlatformDependent.threadLocalRandom().nextInt()`

Result:

No possible contention when random numbers for WebSockets.
---
 .../handler/codec/http/websocketx/WebSocket08FrameEncoder.java | 3 ++-
 .../codec/http/websocketx/WebSocketClientHandshaker00.java     | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocket08FrameEncoder.java b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocket08FrameEncoder.java
index e63f838932..7ae83c35e6 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocket08FrameEncoder.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocket08FrameEncoder.java
@@ -57,6 +57,7 @@ import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.handler.codec.MessageToMessageEncoder;
 import io.netty.handler.codec.TooLongFrameException;
+import io.netty.util.internal.PlatformDependent;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
@@ -178,7 +179,7 @@ public class WebSocket08FrameEncoder extends MessageToMessageEncoder<WebSocketFr
 
             // Write payload
             if (maskPayload) {
-                int random = (int) (Math.random() * Integer.MAX_VALUE);
+                int random = PlatformDependent.threadLocalRandom().nextInt(Integer.MAX_VALUE);
                 mask = ByteBuffer.allocate(4).putInt(random).array();
                 buf.writeBytes(mask);
 
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker00.java b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker00.java
index 55b421bf07..9ccee77af1 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker00.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientHandshaker00.java
@@ -26,6 +26,7 @@ import io.netty.handler.codec.http.HttpHeaders;
 import io.netty.handler.codec.http.HttpMethod;
 import io.netty.handler.codec.http.HttpResponseStatus;
 import io.netty.handler.codec.http.HttpVersion;
+import io.netty.util.internal.PlatformDependent;
 
 import java.net.URI;
 import java.nio.ByteBuffer;
@@ -254,7 +255,7 @@ public class WebSocketClientHandshaker00 extends WebSocketClientHandshaker {
         char[] randomChars = new char[count];
         int randCount = 0;
         while (randCount < count) {
-            int rand = (int) (Math.random() * 0x7e + 0x21);
+            int rand = PlatformDependent.threadLocalRandom().nextInt(0x7e) + 0x21;
             if (0x21 < rand && rand < 0x2f || 0x3a < rand && rand < 0x7e) {
                 randomChars[randCount] = (char) rand;
                 randCount += 1;