From 8e314cdbca74f0a21e634f6baa17b708aa7f17d5 Mon Sep 17 00:00:00 2001
From: Trustin Lee <t@motd.kr>
Date: Sun, 20 Apr 2014 17:54:57 +0900
Subject: [PATCH] Stop ThreadLocalRandom's initial seed generation immediately
 on interruption

Motivation:

ThreadLocalRandomTest reveals that ThreadLocalRandom's initial seed generation loop becomes tight if the thread is interrupted.
We currently interrupt ourselves inside the wait loop, which will raise an InterruptedException again in the next iteration, resulting in infinite (up to 3 seconds) exception construction and thread interruptions.

Modification:

- When the initial seed generator thread is interrupted, break out of the wait loop immediately.
- Log properly when the initial seed generation failed due to interruption.
- When failed to generate the initial seed, interrupt the generator thread just in case the SecureRandom implementation handles it properly.
- Make the initial seed generator thread daemon and handle potential exceptions raised due to the interruption.

Result:

No more tight loop on interruption.  More robust generator thread termination. Fixes #2412
---
 .../util/internal/ThreadLocalRandom.java      | 24 ++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/common/src/main/java/io/netty/util/internal/ThreadLocalRandom.java b/common/src/main/java/io/netty/util/internal/ThreadLocalRandom.java
index 0e9838adf4..d9f7de5a00 100644
--- a/common/src/main/java/io/netty/util/internal/ThreadLocalRandom.java
+++ b/common/src/main/java/io/netty/util/internal/ThreadLocalRandom.java
@@ -25,6 +25,7 @@ package io.netty.util.internal;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
+import java.lang.Thread.UncaughtExceptionHandler;
 import java.security.SecureRandom;
 import java.util.Random;
 import java.util.concurrent.BlockingQueue;
@@ -90,17 +91,27 @@ public class ThreadLocalRandom extends Random {
                     queue.add(random.generateSeed(8));
                 }
             };
+            generatorThread.setDaemon(true);
             generatorThread.start();
+            generatorThread.setUncaughtExceptionHandler(new UncaughtExceptionHandler() {
+                @Override
+                public void uncaughtException(Thread t, Throwable e) {
+                    logger.debug("An exception has been raised by {}", t.getName(), e);
+                }
+            });
 
             // Get the random seed from the thread with timeout.
             final long timeoutSeconds = 3;
             final long deadLine = System.nanoTime() + TimeUnit.SECONDS.toNanos(timeoutSeconds);
+            boolean interrupted = false;
             for (;;) {
                 long waitTime = deadLine - System.nanoTime();
                 if (waitTime <= 0) {
+                    generatorThread.interrupt();
                     logger.warn(
                             "Failed to generate a seed from SecureRandom within {} seconds. " +
-                            "Not enough entrophy?", timeoutSeconds);
+                                    "Not enough entrophy?", timeoutSeconds
+                    );
                     break;
                 }
 
@@ -119,8 +130,10 @@ public class ThreadLocalRandom extends Random {
                         break;
                     }
                 } catch (InterruptedException e) {
-                    // restore interrupt status because we don't know how to/don't need to handle it here
-                    Thread.currentThread().interrupt();
+                    interrupted = true;
+                    generatorThread.interrupt();
+                    logger.warn("Failed to generate a seed from SecureRandom due to an InterruptedException.");
+                    break;
                 }
             }
 
@@ -129,6 +142,11 @@ public class ThreadLocalRandom extends Random {
             initialSeedUniquifier ^= Long.reverse(System.nanoTime());
 
             ThreadLocalRandom.initialSeedUniquifier = initialSeedUniquifier;
+
+            if (interrupted) {
+                // restore interrupt status because we don't know how to/don't need to handle it here
+                Thread.currentThread().interrupt();
+            }
         }
 
         return initialSeedUniquifier;