Merge pull request #349 from dice-group/hotfix/348

Fixed #348 by ensuring that semaphore permits are released.
dice-group · May 1, 2020 · af75d65 · af75d65
2 parents 5f3f330 + 7c986e2
commit af75d65
Showing 1 changed file with 59 additions and 33 deletions.
diff --git a/...main/java/org/aksw/gerbil/semantic/sameas/impl/cache/FileBasedCachingSameAsRetriever.java b/...main/java/org/aksw/gerbil/semantic/sameas/impl/cache/FileBasedCachingSameAsRetriever.java
@@ -111,62 +111,88 @@ public Set<String> retrieveSameURIs(String uri) {
         // if the cache contains the uri, return the set or a set
         // containing only the uri (use the read mutex!!!)
         Set<String> result = null;
+        boolean uriIsCached = false;
         try {
             cacheReadMutex.acquire();
         } catch (InterruptedException e) {
             LOGGER.error("Exception while waiting for read mutex. Returning null.", e);
             return null;
         }
-        boolean uriIsCached = uriSetIdMapping.containsKey(uri);
-        if (uriIsCached) {
-            int setId = uriSetIdMapping.get(uri);
-            if (setId != ENTITY_NOT_FOUND) {
-                result = sets.get(setId);
+        try {
+            uriIsCached = uriSetIdMapping.containsKey(uri);
+            if (uriIsCached) {
+                int setId = uriSetIdMapping.get(uri);
+                if (setId != ENTITY_NOT_FOUND) {
+                    result = sets.get(setId);
+                }
             }
+        } finally {
+            cacheReadMutex.release();
         }
         // If the URI is not in the cache, or it has been cached but the result
         // is null and the request should be retried
         if (!uriIsCached || (uriIsCached && (result == null) && requestEntitiesNotFound)) {
-            cacheReadMutex.release();
-            result = decoratedRetriever.retrieveSameURIs(uri);
+            result = requestUri(uri);
+        }
+        return result;
+    }
+
+    /**
+     * Requests the set for the given URI from the decorated retriever.
+     * 
+     * @param uri
+     * @return
+     */
+    protected Set<String> requestUri(String uri) {
+        Set<String> result = decoratedRetriever.retrieveSameURIs(uri);
+        try {
+            cacheWriteMutex.acquire();
+        } catch (InterruptedException e) {
+            LOGGER.error("Exception while waiting for read mutex. Returning null.", e);
+            return null;
+        }
+        // Make sure that the write mutex is released
+        try {
             try {
-                cacheWriteMutex.acquire();
-                // now we need all others
+                // now we need all other read mutexes
                 cacheReadMutex.acquire(MAX_CONCURRENT_READERS);
             } catch (InterruptedException e) {
                 LOGGER.error("Exception while waiting for read mutex. Returning null.", e);
                 return null;
             }
-            // Check again that nobody already added the uri
-            if (uriSetIdMapping.containsKey(uri)) {
-                // use the cached result
-                int setId = uriSetIdMapping.get(uri);
-                if (setId != ENTITY_NOT_FOUND) {
-                    result = sets.get(setId);
-                } else {
-                    result = null;
-                }
-            } else {
-                if (result != null) {
-                    mergeSetIntoCache(result);
+            // Make sure that the read mutex is released
+            try {
+                // Check again that nobody already added the uri
+                if (uriSetIdMapping.containsKey(uri)) {
+                    // use the cached result
+                    int setId = uriSetIdMapping.get(uri);
+                    if (setId != ENTITY_NOT_FOUND) {
+                        result = sets.get(setId);
+                    } else {
+                        result = null;
+                    }
                 } else {
-                    uriSetIdMapping.put(uri, ENTITY_NOT_FOUND);
-                }
-                ++cacheChanges;
-                if ((forceStorageAfterChanges > 0) && (cacheChanges >= forceStorageAfterChanges)) {
-                    LOGGER.info("Storing the cache has been forced...");
-                    try {
-                        performCacheStorage();
-                    } catch (IOException e) {
-                        LOGGER.error("Exception while writing cache to file. Aborting.", e);
+                    if (result != null) {
+                        mergeSetIntoCache(result);
+                    } else {
+                        uriSetIdMapping.put(uri, ENTITY_NOT_FOUND);
+                    }
+                    ++cacheChanges;
+                    if ((forceStorageAfterChanges > 0) && (cacheChanges >= forceStorageAfterChanges)) {
+                        LOGGER.info("Storing the cache has been forced...");
+                        try {
+                            performCacheStorage();
+                        } catch (IOException e) {
+                            LOGGER.error("Exception while writing cache to file. Aborting.", e);
+                        }
                     }
                 }
+            } finally {
+                cacheReadMutex.release(MAX_CONCURRENT_READERS);
             }
-            // The last one will be released at the end
-            cacheReadMutex.release(MAX_CONCURRENT_READERS - 1);
+        } finally {
             cacheWriteMutex.release();
         }
-        cacheReadMutex.release();
         return result;
     }