fix: wrap timeFragmentMap with Collections.synchronizedMap() for thread safety

PR_DESCRIPTION.md

@@ -0,0 +1,22 @@
+# Fix thread-unsafe LinkedHashMap in TimeTunnelCommand
+
+## Problem
+
+`timeFragmentMap` in `TimeTunnelCommand.java` is a plain `LinkedHashMap` accessed concurrently from multiple threads (advice listeners writing time fragments + command thread reading/iterating). This can cause `ConcurrentModificationException`, infinite loops in HashMap bucket chains, or silent data corruption.
+
+## Root Cause
+
+The field is declared as `new LinkedHashMap<Integer, TimeFragment>()` with a TODO comment acknowledging the thread-safety concern (`// TODO 并非线程安全？` — "not thread safe?"). The `AdviceListener` callbacks that populate this map run on instrumented application threads, while command operations (list, search, replay) run on the Arthas command thread.
+
+## Fix
+
+Replaced `new LinkedHashMap<>()` with `Collections.synchronizedMap(new LinkedHashMap<>())` to provide basic thread safety. Added the `java.util.Collections` import.
+
+## Testing
+
+- Run `tt` command while monitoring a high-throughput method with multiple threads calling it simultaneously.
+- Previously this could cause `ConcurrentModificationException` during `tt -l` (list) operations; now it should be safe.
+
+## Impact
+
+Affects all Arthas users using the Time Tunnel (`tt`) command on multi-threaded applications. The bug is non-deterministic and depends on timing, making it difficult to reproduce consistently.

core/src/main/java/com/taobao/arthas/core/command/monitor200/TimeTunnelCommand.java

@@ -22,6 +22,7 @@
 
 import java.time.LocalDateTime;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -52,7 +53,7 @@
 public class TimeTunnelCommand extends EnhancerCommand {
     // 时间隧道(时间碎片的集合)
     // TODO 并非线程安全？
-    private static final Map<Integer, TimeFragment> timeFragmentMap = new LinkedHashMap<Integer, TimeFragment>();
+    private static final Map<Integer, TimeFragment> timeFragmentMap = Collections.synchronizedMap(new LinkedHashMap<Integer, TimeFragment>());
     // 时间碎片序列生成器
     private static final AtomicInteger sequence = new AtomicInteger(1000);
     // TimeTunnel the method call