Fix race condition in AbstractDataStoreTest.test_aliveField_volatileVisibility

The test had a timing issue where all reader threads could complete before
the writer thread set alive=false, causing the assertion to fail.

Changes:
- Increased observation iterations from 100 to 1000 for longer read duration
- Added 5ms delay in writer thread before setting alive=false
- Start writer thread before reader threads to ensure proper scheduling
- Writer now sets flag while readers are actively reading

This ensures the volatile field visibility can be properly tested without
timing-dependent failures.

Author: claude

src/test/java/org/codelibs/fess/ds/AbstractDataStoreTest.java

@@ -121,13 +121,27 @@ public void test_aliveField_volatileVisibility() throws Exception {
 
         final int readerThreadCount = 10;
         final Thread[] readerThreads = new Thread[readerThreadCount];
-        final boolean[][] observations = new boolean[readerThreadCount][100];
+        final boolean[][] observations = new boolean[readerThreadCount][1000];
+
+        // Writer thread sets alive to false after a small delay
+        Thread writerThread = new Thread(() -> {
+            // Small delay to ensure reader threads are running first
+            try {
+                Thread.sleep(5);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+            dataStore.alive = false;
+        });
+
+        // Start writer thread first
+        writerThread.start();
 
         // Start reader threads that continuously check alive field
         for (int i = 0; i < readerThreadCount; i++) {
             final int threadIndex = i;
             readerThreads[i] = new Thread(() -> {
-                for (int j = 0; j < 100; j++) {
+                for (int j = 0; j < 1000; j++) {
                     observations[threadIndex][j] = dataStore.alive;
                     // Small yield to allow context switching
                     Thread.yield();
@@ -136,11 +150,7 @@ public void test_aliveField_volatileVisibility() throws Exception {
             readerThreads[i].start();
         }
 
-        // Writer thread sets alive to false
-        Thread writerThread = new Thread(() -> {
-            dataStore.alive = false;
-        });
-        writerThread.start();
+        // Wait for writer thread to complete
         writerThread.join();
 
         // Wait for all reader threads to complete
@@ -155,7 +165,7 @@ public void test_aliveField_volatileVisibility() throws Exception {
         // due to volatile ensuring visibility
         int falseCount = 0;
         for (int i = 0; i < readerThreadCount; i++) {
-            for (int j = 0; j < 100; j++) {
+            for (int j = 0; j < 1000; j++) {
                 if (!observations[i][j]) {
                     falseCount++;
                 }