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java/org/apache/tomcat/dbcp/pool2/impl/CallStack.java

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+/*
+ * 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.tomcat.dbcp.pool2.impl;
+
+import java.io.PrintWriter;
+
+/**
+ * Strategy for obtaining and printing the current call stack. This is primarily useful for
+ * {@link org.apache.tomcat.dbcp.pool2.UsageTracking usage tracking} so
+ * that different JVMs and configurations can use more efficient strategies
+ * for obtaining the current call stack depending on metadata needs.
+ *
+ * @see CallStackUtils
+ * @since 2.4.3
+ */
+public interface CallStack {
+
+    /**
+     * Prints the current stack trace if available to a PrintWriter. The format is undefined and is primarily useful
+     * for debugging issues with {@link org.apache.tomcat.dbcp.pool2.PooledObject} usage in user code.
+     *
+     * @param writer a PrintWriter to write the current stack trace to if available
+     * @return true if a stack trace was available to print or false if nothing was printed
+     */
+    boolean printStackTrace(final PrintWriter writer);
+
+    /**
+     * Takes a snapshot of the current call stack. Subsequent calls to {@link #printStackTrace(PrintWriter)} will print
+     * out that stack trace until it is {@linkplain #clear() cleared}.
+     */
+    void fillInStackTrace();
+
+    /**
+     * Clears the current stack trace snapshot. Subsequent calls to {@link #printStackTrace(PrintWriter)} will be
+     * no-ops until another call to {@link #fillInStackTrace()}.
+     */
+    void clear();
+}