1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache license, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the license for the specific language governing permissions and
15 * limitations under the license.
16 */
17 package org.apache.logging.log4j.message;
18
19 import org.apache.logging.log4j.util.PerformanceSensitive;
20 import org.apache.logging.log4j.util.StringBuilderFormattable;
21
22 /**
23 * Messages implementing this interface are reused between logging calls.
24 * <p>
25 * If a Message is reusable, downstream components should not hand over this instance to another thread, but extract its
26 * content (via the {@link StringBuilderFormattable#formatTo(StringBuilder)} method) instead.
27 * </p>
28 * @see ReusableMessageFactory
29 * @since 2.6
30 */
31 @PerformanceSensitive("allocation")
32 public interface ReusableMessage extends Message, StringBuilderFormattable {
33
34 /**
35 * Returns the parameter array that was used to initialize this reusable message and replaces it with the specified
36 * array. The returned parameter array will no longer be modified by this reusable message. The specified array is
37 * now "owned" by this reusable message and can be modified if necessary for the next log event.
38 * </p><p>
39 * ReusableMessages that have no parameters return the specified array.
40 * </p><p>
41 * This method is used by asynchronous loggers to pass the parameter array to a background thread without
42 * allocating new objects.
43 * The actual number of parameters in the returned array can be determined with {@link #getParameterCount()}.
44 * </p>
45 *
46 * @param emptyReplacement the parameter array that can be used for subsequent uses of this reusable message.
47 * This replacement array must have at least 10 elements (the number of varargs supported by the Logger
48 * API).
49 * @return the parameter array for the current message content. This may be a vararg array of any length, or it may
50 * be a reusable array of 10 elements used to hold the unrolled vararg parameters.
51 * @see #getParameterCount()
52 */
53 Object[] swapParameters(Object[] emptyReplacement);
54
55 /**
56 * Returns the number of parameters that was used to initialize this reusable message for the current content.
57 * <p>
58 * The parameter array returned by {@link #swapParameters(Object[])} may be larger than the actual number of
59 * parameters. Callers should use this method to determine how many elements the array contains.
60 * </p>
61 * @return the current number of parameters
62 */
63 short getParameterCount();
64
65 /**
66 * Returns an immutable snapshot of the current internal state of this reusable message. The returned snapshot
67 * will not be affected by subsequent modifications of this reusable message.
68 *
69 * @return an immutable snapshot of this message
70 */
71 Message memento();
72 }