[GitHub] [bookkeeper] merlimat commented on a change in pull request #2710: Impose a memory limit on the bookie journal

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merlimat commented on a change in pull request #2710:
URL: https://github.com/apache/bookkeeper/pull/2710#discussion_r628351476



##########
File path: bookkeeper-common/src/main/java/org/apache/bookkeeper/common/util/MemoryLimitController.java
##########
@@ -0,0 +1,84 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.bookkeeper.common.util;
+
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.ReentrantLock;
+
+public class MemoryLimitController {
+
+    private final long memoryLimit;
+    private final AtomicLong currentUsage = new AtomicLong();
+    private final ReentrantLock mutex = new ReentrantLock(false);
+    private final Condition condition = mutex.newCondition();
+
+    public MemoryLimitController(long memoryLimitBytes) {
+        this.memoryLimit = memoryLimitBytes;
+    }
+
+    public boolean tryReserveMemory(long size) {
+        while (true) {
+            long current = currentUsage.get();
+            long newUsage = current + size;
+
+            // We allow one request to go over the limit, to make the notification
+            // path simpler and more efficient
+            if (current > memoryLimit && memoryLimit > 0) {

Review comment:
       The reason is mostly to leave open the possibility to track how much memory is being used, even if a limit is not being enforced.




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