From 876f7b05914a68ae314e5e420667272cf4415cf9 Mon Sep 17 00:00:00 2001
From: Aleksei Zotov <azotcsit@gmail.com>
Date: Fri, 17 Sep 2021 12:14:12 +0400
Subject: [PATCH] Fix flaky test DatabaseDescriptorRefTest. Patch by Aleksei
 Zotov; reviewed by Ekaterina Dimitrova and John Meredith for CASSANDRA-16862

---
 .../config/DatabaseDescriptorRefTest.java     | 36 ++++++++++++++-----
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/test/unit/org/apache/cassandra/config/DatabaseDescriptorRefTest.java b/test/unit/org/apache/cassandra/config/DatabaseDescriptorRefTest.java
index 1c07a7d88d..791212d275 100644
--- a/test/unit/org/apache/cassandra/config/DatabaseDescriptorRefTest.java
+++ b/test/unit/org/apache/cassandra/config/DatabaseDescriptorRefTest.java
@@ -35,6 +35,7 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 import org.junit.Test;
 
@@ -145,6 +146,7 @@ public class DatabaseDescriptorRefTest
     static final Set<String> checkedClasses = new HashSet<>(Arrays.asList(validClasses));
 
     @Test
+    @SuppressWarnings({"DynamicRegexReplaceableByCompiledPattern", "UseOfSystemOutOrSystemErr"})
     public void testDatabaseDescriptorRef() throws Throwable
     {
         PrintStream out = System.out;
@@ -152,6 +154,7 @@ public class DatabaseDescriptorRefTest
 
         ThreadMXBean threads = ManagementFactory.getThreadMXBean();
         int threadCount = threads.getThreadCount();
+        List<Long> existingThreadIDs = Arrays.stream(threads.getAllThreadIds()).boxed().collect(Collectors.toList());
 
         ClassLoader delegate = Thread.currentThread().getContextClassLoader();
 
@@ -210,7 +213,29 @@ public class DatabaseDescriptorRefTest
 
         assertEquals("thread started", threadCount, threads.getThreadCount());
 
-        Class cDatabaseDescriptor = Class.forName("org.apache.cassandra.config.DatabaseDescriptor", true, cl);
+        Class<?> databaseDescriptorClass = Class.forName("org.apache.cassandra.config.DatabaseDescriptor", true, cl);
+
+        // During DatabaseDescriptor instantiation some threads are spawned. We need to take them into account in
+        // threadCount variable, otherwise they will be considered as new threads spawned by methods below. There is a
+        // trick: in case of multiple runs of this test in the same JVM the number of such threads will be multiplied by
+        // the number of runs. That's because DatabaseDescriptor is instantiated via a different class loader. So in
+        // order to keep calculation logic correct, we ignore existing threads that were spawned during the previous
+        // runs and change threadCount variable for the new threads only (if they have some specific names).
+        for (ThreadInfo threadInfo : threads.getThreadInfo(threads.getAllThreadIds()))
+        {
+            // All existing threads have been already taken into account in threadCount variable, so we ignore them
+            if (existingThreadIDs.contains(threadInfo.getThreadId()))
+                continue;
+            // Logback AsyncAppender thread needs to be taken into account
+            if (threadInfo.getThreadName().equals("AsyncAppender-Worker-ASYNC"))
+                threadCount++;
+            // Logback basic threads need to be taken into account
+            if (threadInfo.getThreadName().matches("logback-\\d+"))
+                threadCount++;
+            // Dynamic Attach thread needs to be taken into account, generally it is spawned by IDE
+            if (threadInfo.getThreadName().equals("Attach Listener"))
+                threadCount++;
+        }
 
         for (String methodName : new String[]{
             "clientInitialization",
@@ -228,16 +253,9 @@ public class DatabaseDescriptorRefTest
             // "applyRequestScheduler",
         })
         {
-            Method method = cDatabaseDescriptor.getDeclaredMethod(methodName);
+            Method method = databaseDescriptorClass.getDeclaredMethod(methodName);
             method.invoke(null);
 
-            if ("clientInitialization".equals(methodName) &&
-                threadCount + 1 == threads.getThreadCount())
-            {
-                // ignore the "AsyncAppender-Worker-ASYNC" thread
-                threadCount++;
-            }
-
             if (threadCount != threads.getThreadCount())
             {
                 for (ThreadInfo threadInfo : threads.getThreadInfo(threads.getAllThreadIds()))