[Backport 2.x] Clear ehcache disk cache files during initialization

plugins/cache-ehcache/src/main/java/org/opensearch/cache/store/disk/EhcacheDiskCache.java

@@ -60,7 +60,6 @@
 import java.util.function.ToLongBiFunction;
 
 import org.ehcache.Cache;
-import org.ehcache.CachePersistenceException;
 import org.ehcache.PersistentCacheManager;
 import org.ehcache.config.builders.CacheConfigurationBuilder;
 import org.ehcache.config.builders.CacheEventListenerConfigurationBuilder;
@@ -104,8 +103,6 @@ public class EhcacheDiskCache<K, V> implements ICache<K, V> {
     // Unique id associated with this cache.
     private final static String UNIQUE_ID = UUID.randomUUID().toString();
     private final static String THREAD_POOL_ALIAS_PREFIX = "ehcachePool";
-    private final static int MINIMUM_MAX_SIZE_IN_BYTES = 1024 * 100; // 100KB
-
     // A Cache manager can create many caches.
     private final PersistentCacheManager cacheManager;
 
@@ -127,13 +124,18 @@ public class EhcacheDiskCache<K, V> implements ICache<K, V> {
     private final Serializer<K, byte[]> keySerializer;
     private final Serializer<V, byte[]> valueSerializer;
 
+    final static int MINIMUM_MAX_SIZE_IN_BYTES = 1024 * 100; // 100KB
+    final static String CACHE_DATA_CLEANUP_DURING_INITIALIZATION_EXCEPTION = "Failed to delete ehcache disk cache under "
+        + "path: %s during initialization. Please clean this up manually and restart the process";
+
     /**
      * Used in computeIfAbsent to synchronize loading of a given key. This is needed as ehcache doesn't provide a
      * computeIfAbsent method.
      */
     Map<ICacheKey<K>, CompletableFuture<Tuple<ICacheKey<K>, V>>> completableFutureMap = new ConcurrentHashMap<>();
 
-    private EhcacheDiskCache(Builder<K, V> builder) {
+    @SuppressForbidden(reason = "Ehcache uses File.io")
+    EhcacheDiskCache(Builder<K, V> builder) {
         this.keyType = Objects.requireNonNull(builder.keyType, "Key type shouldn't be null");
         this.valueType = Objects.requireNonNull(builder.valueType, "Value type shouldn't be null");
         this.expireAfterAccess = Objects.requireNonNull(builder.getExpireAfterAcess(), "ExpireAfterAccess value shouldn't " + "be null");
@@ -151,6 +153,18 @@ private EhcacheDiskCache(Builder<K, V> builder) {
         if (this.storagePath == null || this.storagePath.isBlank()) {
             throw new IllegalArgumentException("Storage path shouldn't be null or empty");
         }
+        // Delete all the previous disk cache related files/data. We don't persist data between process restart for
+        // now which is why need to do this. Clean up in case there was a non graceful restart and we had older disk
+        // cache data still lying around.
+        Path ehcacheDirectory = Paths.get(this.storagePath);
+        if (Files.exists(ehcacheDirectory)) {
+            try {
+                logger.info("Found older disk cache data lying around during initialization under path: {}", this.storagePath);
+                IOUtils.rm(ehcacheDirectory);
+            } catch (IOException e) {
+                throw new OpenSearchException(String.format(CACHE_DATA_CLEANUP_DURING_INITIALIZATION_EXCEPTION, this.storagePath), e);
+            }
+        }
         if (builder.threadPoolAlias == null || builder.threadPoolAlias.isBlank()) {
             this.threadPoolAlias = THREAD_POOL_ALIAS_PREFIX + "DiskWrite#" + UNIQUE_ID;
         } else {
@@ -175,6 +189,11 @@ private EhcacheDiskCache(Builder<K, V> builder) {
         }
     }
 
+    // Package private for testing
+    PersistentCacheManager getCacheManager() {
+        return this.cacheManager;
+    }
+
     @SuppressWarnings({ "rawtypes" })
     private Cache<ICacheKey, ByteArrayWrapper> buildCache(Duration expireAfterAccess, Builder<K, V> builder) {
         // Creating the cache requires permissions specified in plugin-security.policy
@@ -255,7 +274,7 @@ Map<ICacheKey<K>, CompletableFuture<Tuple<ICacheKey<K>, V>>> getCompletableFutur
     }
 
     @SuppressForbidden(reason = "Ehcache uses File.io")
-    private PersistentCacheManager buildCacheManager() {
+    PersistentCacheManager buildCacheManager() {
         // In case we use multiple ehCaches, we can define this cache manager at a global level.
         // Creating the cache manager also requires permissions specified in plugin-security.policy
         return AccessController.doPrivileged((PrivilegedAction<PersistentCacheManager>) () -> {
@@ -444,20 +463,21 @@ public void refresh() {
     @Override
     @SuppressForbidden(reason = "Ehcache uses File.io")
     public void close() {
-        cacheManager.removeCache(this.diskCacheAlias);
-        cacheManager.close();
         try {
-            cacheManager.destroyCache(this.diskCacheAlias);
-            // Delete all the disk cache related files/data
-            Path ehcacheDirectory = Paths.get(this.storagePath);
-            if (Files.exists(ehcacheDirectory)) {
+            cacheManager.close();
+        } catch (Exception e) {
+            logger.error(() -> new ParameterizedMessage("Exception occurred while trying to close ehcache manager"), e);
+        }
+        // Delete all the disk cache related files/data in case it is present
+        Path ehcacheDirectory = Paths.get(this.storagePath);
+        if (Files.exists(ehcacheDirectory)) {
+            try {
                 IOUtils.rm(ehcacheDirectory);
+            } catch (IOException e) {
+                logger.error(() -> new ParameterizedMessage("Failed to delete ehcache disk cache data under path: {}", this.storagePath));
             }
-        } catch (CachePersistenceException e) {
-            throw new OpenSearchException("Exception occurred while destroying ehcache and associated data", e);
-        } catch (IOException e) {
-            logger.error(() -> new ParameterizedMessage("Failed to delete ehcache disk cache data under path: {}", this.storagePath));
         }
+
     }
 
     /**