Migrate test CountdownEvent usage to Java-style CountDownLatch, #1284

Replaces System.Threading.CountdownEvent with the new
Lucene.Net.Support.Threading.CountDownLatch across 22 test files where
the upstream Java equivalent uses java.util.concurrent.CountDownLatch.

Mechanical changes:
- type rename: CountdownEvent -> CountDownLatch
- .Signal() -> .CountDown()
- .Wait() / .Wait(TimeSpan) -> .Await() / .Await(TimeSpan)
- .CurrentCount -> .Count
- .IsSet -> .Count == 0
- added using Lucene.Net.Support.Threading where needed

Workarounds for CountdownEvent.Signal()'s "throws past zero" behavior
that are now redundant (CountDown is idempotent at zero, matching Java):
- TestConcurrentMergeScheduler.TestMaxMergeCount: removed the
  CurrentCount > 0 guard. This was the trigger for the CI failure on
  Windows .NET Framework and Ubuntu .NET 8 after the LUCENE-5871 port
  made Shutdown(false) flush more aggressively.
- TestIndexWriterWithThreads: removed the same pre-existing guard at
  iwConstructed.
- TestDocumentsWriterStallControl: removed if (!updateJoin.IsSet)
  guard around CountDown(); upstream calls countDown() unconditionally.
- TestControlledRealTimeReopenThread: replaced two
  signal.Reset(Count - 1)/latch.Reset(Count - 1) hacks with plain
  CountDown(), matching upstream signal.countDown()/latch.countDown().

Other adjustments:
- BaseDocValuesFormatTestCase: dropped `using` keyword on two latches.
  CountdownEvent was IDisposable; CountDownLatch isn't (Java's isn't
  either), so the latches now go out of scope without explicit cleanup.
- TestControlledRealTimeReopenThread.LatchedIndexWriter: ctor changed
  from public to internal so CountDownLatch (internal) is reachable
  from a public class member.

Files touched: 22 test files plus 2 in TestFramework. All ported sites
now read the same as the upstream Java; no LUCENENET notes were added
because the code is now equivalent.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: paulirwin

src/Lucene.Net.TestFramework/Analysis/BaseTokenStreamTestCase.cs

@@ -17,6 +17,7 @@
 using Attribute = Lucene.Net.Util.Attribute;
 using Directory = Lucene.Net.Store.Directory;
 using JCG = J2N.Collections.Generic;
+using Lucene.Net.Support.Threading;
 
 namespace Lucene.Net.Analysis
 {
@@ -629,15 +630,15 @@ internal class AnalysisThread : ThreadJob
             internal readonly bool simple;
             internal readonly bool offsetsAreCorrect;
             internal readonly RandomIndexWriter iw;
-            private readonly CountdownEvent latch;
+            private readonly CountDownLatch latch;
 
             // NOTE: not volatile because we don't want the tests to
             // add memory barriers (ie alter how threads
             // interact)... so this is just "best effort":
             public bool Failed { get; set; }
             public Exception FirstException { get; set; } = null;
 
-            internal AnalysisThread(long seed, CountdownEvent latch, Analyzer a, int iterations, int maxWordLength,
+            internal AnalysisThread(long seed, CountDownLatch latch, Analyzer a, int iterations, int maxWordLength,
                 bool useCharFilter, bool simple, bool offsetsAreCorrect, RandomIndexWriter iw)
             {
                 this.seed = seed;
@@ -656,7 +657,7 @@ public override void Run()
                 bool success = false;
                 try
                 {
-                    if (latch != null) latch.Wait();
+                    if (latch != null) latch.Await();
                     // see the part in checkRandomData where it replays the same text again
                     // to verify reproducability/reuse: hopefully this would catch thread hazards.
                     CheckRandomData(new J2N.Randomizer(seed), a, iterations, maxWordLength, useCharFilter, simple, offsetsAreCorrect, iw);
@@ -710,7 +711,7 @@ public static void CheckRandomData(Random random, Analyzer a, int iterations, in
                 // now test with multiple threads: note we do the EXACT same thing we did before in each thread,
                 // so this should only really fail from another thread if its an actual thread problem
                 int numThreads = TestUtil.NextInt32(random, 2, 4);
-                var startingGun = new CountdownEvent(1);
+                var startingGun = new CountDownLatch(1);
                 var threads = new AnalysisThread[numThreads];
                 for (int i = 0; i < threads.Length; i++)
                 {
@@ -722,7 +723,7 @@ public static void CheckRandomData(Random random, Analyzer a, int iterations, in
                     thread.Start();
                 }
 
-                startingGun.Signal();
+                startingGun.CountDown();
                 foreach (var t in threads)
                 {
                     try

src/Lucene.Net.TestFramework/Index/BaseDocValuesFormatTestCase.cs

@@ -18,6 +18,7 @@
 using Assert = Lucene.Net.TestFramework.Assert;
 using JCG = J2N.Collections.Generic;
 using Test = NUnit.Framework.TestAttribute;
+using Lucene.Net.Support.Threading;
 
 namespace Lucene.Net.Index
 {
@@ -3243,13 +3244,13 @@ public virtual void TestThreads()
             using DirectoryReader ir = DirectoryReader.Open(dir);
             int numThreads = TestUtil.NextInt32(Random, 2, 7);
             ThreadJob[] threads = new ThreadJob[numThreads];
-            using CountdownEvent startingGun = new CountdownEvent(1);
+            CountDownLatch startingGun = new CountDownLatch(1);
             for (int i = 0; i < threads.Length; i++)
             {
                 threads[i] = new ThreadAnonymousClass(ir, startingGun);
                 threads[i].Start();
             }
-            startingGun.Signal();
+            startingGun.CountDown();
             foreach (ThreadJob t in threads)
             {
                 t.Join();
@@ -3259,9 +3260,9 @@ public virtual void TestThreads()
         private sealed class ThreadAnonymousClass : ThreadJob
         {
             private readonly DirectoryReader ir;
-            private readonly CountdownEvent startingGun;
+            private readonly CountDownLatch startingGun;
 
-            public ThreadAnonymousClass(DirectoryReader ir, CountdownEvent startingGun)
+            public ThreadAnonymousClass(DirectoryReader ir, CountDownLatch startingGun)
             {
                 this.ir = ir;
                 this.startingGun = startingGun;
@@ -3271,7 +3272,7 @@ public override void Run()
             {
                 try
                 {
-                    startingGun.Wait();
+                    startingGun.Await();
                     BytesRef scratch = new BytesRef(); // LUCENENET: Moved outside of the loop for performance
                     foreach (AtomicReaderContext context in ir.Leaves)
                     {
@@ -3379,13 +3380,13 @@ public virtual void TestThreads2()
             using DirectoryReader ir = DirectoryReader.Open(dir);
             int numThreads = TestUtil.NextInt32(Random, 2, 7);
             ThreadJob[] threads = new ThreadJob[numThreads];
-            using CountdownEvent startingGun = new CountdownEvent(1);
+            CountDownLatch startingGun = new CountDownLatch(1);
             for (int i = 0; i < threads.Length; i++)
             {
                 threads[i] = new ThreadAnonymousClass2(ir, startingGun);
                 threads[i].Start();
             }
-            startingGun.Signal();
+            startingGun.CountDown();
             foreach (ThreadJob t in threads)
             {
                 t.Join();
@@ -3395,9 +3396,9 @@ public virtual void TestThreads2()
         private sealed class ThreadAnonymousClass2 : ThreadJob
         {
             private readonly DirectoryReader ir;
-            private readonly CountdownEvent startingGun;
+            private readonly CountDownLatch startingGun;
 
-            public ThreadAnonymousClass2(DirectoryReader ir, CountdownEvent startingGun)
+            public ThreadAnonymousClass2(DirectoryReader ir, CountDownLatch startingGun)
             {
                 this.ir = ir;
                 this.startingGun = startingGun;
@@ -3407,7 +3408,7 @@ public override void Run()
             {
                 try
                 {
-                    startingGun.Wait();
+                    startingGun.Await();
                     foreach (AtomicReaderContext context in ir.Leaves)
                     {
                         AtomicReader r = context.AtomicReader;

src/Lucene.Net.Tests/Index/TestBagOfPositions.cs

@@ -117,7 +117,7 @@ public virtual void Test()
             // else just positions
 
             ThreadJob[] threads = new ThreadJob[threadCount];
-            CountdownEvent startingGun = new CountdownEvent(1);
+            CountDownLatch startingGun = new CountDownLatch(1);
 
             for (int threadID = 0; threadID < threadCount; threadID++)
             {
@@ -128,7 +128,7 @@ public virtual void Test()
                 threads[threadID] = new ThreadAnonymousClass(maxTermsPerDoc, postings, iw, startingGun, threadRandom, document, field);
                 threads[threadID].Start();
             }
-            startingGun.Signal();
+            startingGun.CountDown();
             foreach (ThreadJob t in threads)
             {
                 t.Join();
@@ -160,12 +160,12 @@ private sealed class ThreadAnonymousClass : ThreadJob
             private readonly int maxTermsPerDoc;
             private readonly ConcurrentQueue<string> postings;
             private readonly RandomIndexWriter iw;
-            private readonly CountdownEvent startingGun;
+            private readonly CountDownLatch startingGun;
             private readonly Random threadRandom;
             private readonly Document document;
             private readonly Field field;
 
-            public ThreadAnonymousClass(int maxTermsPerDoc, ConcurrentQueue<string> postings, RandomIndexWriter iw, CountdownEvent startingGun, Random threadRandom, Document document, Field field)
+            public ThreadAnonymousClass(int maxTermsPerDoc, ConcurrentQueue<string> postings, RandomIndexWriter iw, CountDownLatch startingGun, Random threadRandom, Document document, Field field)
             {
                 this.maxTermsPerDoc = maxTermsPerDoc;
                 this.postings = postings;
@@ -180,7 +180,7 @@ public override void Run()
             {
                 try
                 {
-                    startingGun.Wait();
+                    startingGun.Await();
                     while (!postings.IsEmpty)
                     {
                         StringBuilder text = new StringBuilder();

src/Lucene.Net.Tests/Index/TestBagOfPostings.cs

@@ -96,14 +96,14 @@ public virtual void Test()
             }
 
             ThreadJob[] threads = new ThreadJob[threadCount];
-            CountdownEvent startingGun = new CountdownEvent(1);
+            CountDownLatch startingGun = new CountDownLatch(1);
 
             for (int threadID = 0; threadID < threadCount; threadID++)
             {
                 threads[threadID] = new ThreadAnonymousClass(maxTermsPerDoc, postings, iw, startingGun);
                 threads[threadID].Start();
             }
-            startingGun.Signal();
+            startingGun.CountDown();
             foreach (ThreadJob t in threads)
             {
                 t.Join();
@@ -141,9 +141,9 @@ private sealed class ThreadAnonymousClass : ThreadJob
             private readonly int maxTermsPerDoc;
             private readonly ConcurrentQueue<string> postings;
             private readonly RandomIndexWriter iw;
-            private readonly CountdownEvent startingGun;
+            private readonly CountDownLatch startingGun;
 
-            public ThreadAnonymousClass(int maxTermsPerDoc, ConcurrentQueue<string> postings, RandomIndexWriter iw, CountdownEvent startingGun)
+            public ThreadAnonymousClass(int maxTermsPerDoc, ConcurrentQueue<string> postings, RandomIndexWriter iw, CountDownLatch startingGun)
             {
                 this.maxTermsPerDoc = maxTermsPerDoc;
                 this.postings = postings;
@@ -158,7 +158,7 @@ public override void Run()
                     Document document = new Document();
                     Field field = NewTextField("field", "", Field.Store.NO);
                     document.Add(field);
-                    startingGun.Wait();
+                    startingGun.Await();
                     while (!postings.IsEmpty)
                     {
                         StringBuilder text = new StringBuilder();

src/Lucene.Net.Tests/Index/TestBinaryDocValuesUpdates.cs

@@ -18,6 +18,7 @@
 using System.Threading;
 using Assert = Lucene.Net.TestFramework.Assert;
 using JCG = J2N.Collections.Generic;
+using Lucene.Net.Support.Threading;
 
 namespace Lucene.Net.Index
 {
@@ -1200,7 +1201,7 @@ public virtual void TestStressMultiThreading()
                 writer.AddDocument(doc);
             }
 
-            CountdownEvent done = new CountdownEvent(numThreads);
+            CountDownLatch done = new CountDownLatch(numThreads);
             AtomicInt32 numUpdates = new AtomicInt32(AtLeast(100));
 
             // same thread updates a field as well as reopens
@@ -1216,7 +1217,7 @@ public virtual void TestStressMultiThreading()
             {
                 t.Start();
             }
-            done.Wait();
+            done.Await();
             writer.Dispose();
 
             DirectoryReader reader = DirectoryReader.Open(dir);
@@ -1253,12 +1254,12 @@ private sealed class ThreadAnonymousClass : ThreadJob
         {
             private readonly IndexWriter writer;
             private readonly int numDocs;
-            private readonly CountdownEvent done;
+            private readonly CountDownLatch done;
             private readonly AtomicInt32 numUpdates;
             private readonly string f;
             private readonly string cf;
 
-            public ThreadAnonymousClass(string str, IndexWriter writer, int numDocs, CountdownEvent done, AtomicInt32 numUpdates, string f, string cf)
+            public ThreadAnonymousClass(string str, IndexWriter writer, int numDocs, CountDownLatch done, AtomicInt32 numUpdates, string f, string cf)
                 : base(str)
             {
                 this.writer = writer;
@@ -1365,7 +1366,7 @@ public override void Run()
                             }
                         }
                     }
-                    done.Signal();
+                    done.CountDown();
                 }
             }
         }

src/Lucene.Net.Tests/Index/TestConcurrentMergeScheduler.cs

@@ -3,6 +3,7 @@
 using Lucene.Net.Documents;
 using Lucene.Net.Index.Extensions;
 using Lucene.Net.Store;
+using Lucene.Net.Support.Threading;
 using Lucene.Net.Util;
 using NUnit.Framework;
 using RandomizedTesting.Generators;
@@ -286,7 +287,7 @@ public virtual void TestMaxMergeCount()
 
             int maxMergeCount = TestUtil.NextInt32(Random, 1, 5);
             int maxMergeThreads = TestUtil.NextInt32(Random, 1, maxMergeCount);
-            CountdownEvent enoughMergesWaiting = new CountdownEvent(maxMergeCount);
+            CountDownLatch enoughMergesWaiting = new CountDownLatch(maxMergeCount);
             AtomicInt32 runningMergeCount = new AtomicInt32(0);
             AtomicBoolean failed = new AtomicBoolean();
 
@@ -308,7 +309,7 @@ public virtual void TestMaxMergeCount()
             IndexWriter w = new IndexWriter(dir, iwc);
             Document doc = new Document();
             doc.Add(NewField("field", "field", TextField.TYPE_NOT_STORED));
-            while (enoughMergesWaiting.CurrentCount != 0 && !failed)
+            while (enoughMergesWaiting.Count != 0 && !failed)
             {
                 for (int i = 0; i < 10; i++)
                 {
@@ -322,11 +323,11 @@ public virtual void TestMaxMergeCount()
         private sealed class ConcurrentMergeSchedulerAnonymousClass : ConcurrentMergeScheduler
         {
             private readonly int maxMergeCount;
-            private readonly CountdownEvent enoughMergesWaiting;
+            private readonly CountDownLatch enoughMergesWaiting;
             private readonly AtomicInt32 runningMergeCount;
             private readonly AtomicBoolean failed;
 
-            public ConcurrentMergeSchedulerAnonymousClass(int maxMergeCount, CountdownEvent enoughMergesWaiting, AtomicInt32 runningMergeCount, AtomicBoolean failed)
+            public ConcurrentMergeSchedulerAnonymousClass(int maxMergeCount, CountDownLatch enoughMergesWaiting, AtomicInt32 runningMergeCount, AtomicBoolean failed)
             {
                 this.maxMergeCount = maxMergeCount;
                 this.enoughMergesWaiting = enoughMergesWaiting;
@@ -344,14 +345,14 @@ protected internal override void DoMerge(MergePolicy.OneMerge merge)
                     try
                     {
                         Assert.IsTrue(count <= maxMergeCount, "count=" + count + " vs maxMergeCount=" + maxMergeCount);
-                        enoughMergesWaiting.Signal();
+                        enoughMergesWaiting.CountDown();
 
                         // Stall this merge until we see exactly
                         // maxMergeCount merges waiting
                         while (true)
                         {
                             // wait for 10 milliseconds
-                            if (enoughMergesWaiting.Wait(new TimeSpan(0, 0, 0, 0, 10)) || failed)
+                            if (enoughMergesWaiting.Await(new TimeSpan(0, 0, 0, 0, 10)) || failed)
                             {
                                 break;
                             }

src/Lucene.Net.Tests/Index/TestDocValuesIndexing.cs

@@ -7,6 +7,7 @@
 using System;
 using System.Threading;
 using Assert = Lucene.Net.TestFramework.Assert;
+using Lucene.Net.Support.Threading;
 
 namespace Lucene.Net.Index
 {
@@ -513,7 +514,7 @@ public virtual void TestMixedTypesDifferentThreads()
             Directory dir = NewDirectory();
             IndexWriter w = new IndexWriter(dir, NewIndexWriterConfig(TEST_VERSION_CURRENT, new MockAnalyzer(Random)));
 
-            CountdownEvent startingGun = new CountdownEvent(1);
+            CountDownLatch startingGun = new CountDownLatch(1);
             AtomicBoolean hitExc = new AtomicBoolean();
             ThreadJob[] threads = new ThreadJob[3];
             for (int i = 0; i < 3; i++)
@@ -538,7 +539,7 @@ public virtual void TestMixedTypesDifferentThreads()
                 threads[i].Start();
             }
 
-            startingGun.Signal();
+            startingGun.CountDown();
 
             foreach (ThreadJob t in threads)
             {
@@ -552,11 +553,11 @@ public virtual void TestMixedTypesDifferentThreads()
         private sealed class ThreadAnonymousClass : ThreadJob
         {
             private readonly IndexWriter w;
-            private readonly CountdownEvent startingGun;
+            private readonly CountDownLatch startingGun;
             private readonly AtomicBoolean hitExc;
             private readonly Document doc;
 
-            public ThreadAnonymousClass(IndexWriter w, CountdownEvent startingGun, AtomicBoolean hitExc, Document doc)
+            public ThreadAnonymousClass(IndexWriter w, CountDownLatch startingGun, AtomicBoolean hitExc, Document doc)
             {
                 this.w = w;
                 this.startingGun = startingGun;
@@ -568,7 +569,7 @@ public override void Run()
             {
                 try
                 {
-                    startingGun.Wait();
+                    startingGun.Await();
                     w.AddDocument(doc);
                 }
                 catch (Exception iae) when (iae.IsIllegalArgumentException())