Move to kernel style SPDX license identifiers

[lttng-ust.git] / liblttng-ust-java-agent / java / lttng-ust-agent-common / org / lttng / ust / agent / context / ContextInfoManager.java

diff --git a/liblttng-ust-java-agent/java/lttng-ust-agent-common/org/lttng/ust/agent/context/ContextInfoManager.java b/liblttng-ust-java-agent/java/lttng-ust-agent-common/org/lttng/ust/agent/context/ContextInfoManager.java
index 86ded59b346ab6984ca4594826d4d9f5716cb5d4..22efe022e794c3b1930570f560df5b408567ea2a 100644 (file)
--- a/liblttng-ust-java-agent/java/lttng-ust-agent-common/org/lttng/ust/agent/context/ContextInfoManager.java
+++ b/liblttng-ust-java-agent/java/lttng-ust-agent-common/org/lttng/ust/agent/context/ContextInfoManager.java
@@ -1,18 +1,8 @@
 /*
- * Copyright (C) 2015 - EfficiOS Inc., Alexandre Montplaisir <alexmonthy@efficios.com>
+ * SPDX-License-Identifier: LGPL-2.1-only
  *
- * This library is free software; you can redistribute it and/or modify it
- * under the terms of the GNU Lesser General Public License, version 2.1 only,
- * as published by the Free Software Foundation.
- *
- * This library is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
- * for more details.
- *
- * You should have received a copy of the GNU Lesser General Public License
- * along with this library; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ * Copyright (C) 2015 EfficiOS Inc.
+ * Copyright (C) 2015 Alexandre Montplaisir <alexmonthy@efficios.com>
  */
 
 package org.lttng.ust.agent.context;
@@ -40,6 +30,10 @@ public final class ContextInfoManager {
        private final Map<String, IContextInfoRetriever> contextInfoRetrievers = new ConcurrentHashMap<String, IContextInfoRetriever>();
        private final Map<String, Long> contextInforRetrieverRefs = new HashMap<String, Long>();
 
+       /**
+        * Lock used to keep the two maps above in sync when retrievers are
+        * registered or unregistered.
+        */
        private final Object retrieverLock = new Object();
 
        /** Singleton class, constructor should not be accessed directly */
@@ -163,6 +157,13 @@ public final class ContextInfoManager {
         *         was none
         */
        public IContextInfoRetriever getContextInfoRetriever(String retrieverName) {
+               /*
+                * Note that this method does not take the retrieverLock, it lets
+                * concurrent threads access the ConcurrentHashMap directly.
+                *
+                * It's fine for a get() to happen during a registration or
+                * unregistration, it's first-come-first-serve.
+                */
                return contextInfoRetrievers.get(retrieverName);
        }