[GitHub] [beam] zhoufek commented on a change in pull request #15037: [BEAM-12474] Write PubsubIO parsing errors to dead-letter topic

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zhoufek commented on a change in pull request #15037:
URL: https://github.com/apache/beam/pull/15037#discussion_r657330871



##########
File path: sdks/java/core/src/main/java/org/apache/beam/sdk/util/ComparableThrowable.java
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@@ -0,0 +1,112 @@
+/*
+ * 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.beam.sdk.util;
+
+import java.io.Serializable;
+import java.util.Arrays;
+import javax.annotation.Nullable;
+
+/**
+ * A wrapper around a {@link Throwable} for use with coders.
+ *
+ * <p>The {@link Throwable} class is serializable. However, it, along with man child classes like
+ * {@link Exception}, does not override {@link Object#equals(Object)}. As a result, t1.equals(t2)
+ * will return false if t2 is a deserialized instance of serialized t1. This makes it appear as if
+ * coders are mutating the value, which can lead to things like log spam. This wrapper overrides
+ * {@link Object#equals(Object)} to get around this issue. The hash code remains the same as the
+ * underlying {@link Throwable}.
+ *
+ * <p>The equality comparison is transitive, meaning that for two {@link Throwable}s t1 and t2, the
+ * causes must be equal. This can occur either because they are both null or because they are both
+ * equal after being wrapped.
+ *
+ * <p>Note that this is simply a best effort based on properties like instance type, stack trace,
+ * message, and cause. It cannot guarantee that the state that led to the exception is the same,
+ * unless it is fully captured in the message, nor can it differentiate between two exceptions
+ * thrown at different times or in different processes. For this reason, this is not suitable for a
+ * general-purpose {@link Throwable} equality comparison. It merely exists to try to avoid false
+ * positives in a mutation check for coders.
+ *
+ * <p>Due to the above, this does not support comparison to a raw {@link Throwable}.
+ */
+public class ComparableThrowable implements Serializable {

Review comment:
       Willing to accept suggestions on a different name. The best I could come up with is ComparableThrowable, but that might be confusing due to not implementing the Comparable interface. I guess implementing the interface is itself an option, but I don't think there's much value in that.




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