[tinkerpop] 01/01: TINKERPOP-2126 Fixed concurrency issue in `ObjectWritable::toString()`.

[dk...@apache.org]

This is an automated email from the ASF dual-hosted git repository.

dkuppitz pushed a commit to branch TINKERPOP-2126
in repository https://gitbox.apache.org/repos/asf/tinkerpop.git

commit 960ec6071dfc323a373fb8b7f83e657e336acd08
Author: Daniel Kuppitz <da...@hotmail.com>
AuthorDate: Tue Jan 22 15:07:09 2019 -0700

    TINKERPOP-2126 Fixed concurrency issue in `ObjectWritable::toString()`.
---
 CHANGELOG.asciidoc                                        |  2 +-
 .../gremlin/hadoop/structure/io/ObjectWritable.java       | 15 ++++++++++++---
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.asciidoc b/CHANGELOG.asciidoc
index 1b0f79b..eac7a9b 100644
--- a/CHANGELOG.asciidoc
+++ b/CHANGELOG.asciidoc
@@ -24,7 +24,7 @@ image::https://raw.githubusercontent.com/apache/tinkerpop/master/docs/static/ima
 === TinkerPop 3.3.6 (Release Date: NOT OFFICIALLY RELEASED YET)
 
 * Masked sensitive configuration options in the logs of `KryoShimServiceLoader`.
-* Fixed a concurrency issue in `TraverserSet`
+* Fixed concurrency issues in `TraverserSet::toString()` and `ObjectWritable::toString()`.
 * Fixed a bug in `InlineFilterStrategy` that mixed up and's and or's when folding merging conditions together.
 
 [[release-3-3-5]]
diff --git a/hadoop-gremlin/src/main/java/org/apache/tinkerpop/gremlin/hadoop/structure/io/ObjectWritable.java b/hadoop-gremlin/src/main/java/org/apache/tinkerpop/gremlin/hadoop/structure/io/ObjectWritable.java
index 0379ee6..13cea4e 100644
--- a/hadoop-gremlin/src/main/java/org/apache/tinkerpop/gremlin/hadoop/structure/io/ObjectWritable.java
+++ b/hadoop-gremlin/src/main/java/org/apache/tinkerpop/gremlin/hadoop/structure/io/ObjectWritable.java
@@ -30,13 +30,14 @@ import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.io.Serializable;
+import java.util.ConcurrentModificationException;
+import java.util.Objects;
 
 /**
  * @author Marko A. Rodriguez (http://markorodriguez.com)
  */
 public final class ObjectWritable<T> implements WritableComparable<ObjectWritable>, Serializable {
 
-    private static final String NULL = "null";
     private static final ObjectWritable<MapReduce.NullObject> NULL_OBJECT_WRITABLE = new ObjectWritable<>(MapReduce.NullObject.instance());
 
     T t;
@@ -45,7 +46,7 @@ public final class ObjectWritable<T> implements WritableComparable<ObjectWritabl
     }
 
     public ObjectWritable(final T t) {
-        this.t = t;
+        this.set(t);
     }
 
     public T get() {
@@ -58,7 +59,15 @@ public final class ObjectWritable<T> implements WritableComparable<ObjectWritabl
 
     @Override
     public String toString() {
-        return null == this.t ? NULL : this.t.toString();
+        // Spark's background logging apparently tries to log a `toString()` of certain objects while they're being
+        // modified, which then throws a ConcurrentModificationException. We probably can't make any arbitrary object
+        // thread-safe, but we can easily retry on such cases and eventually we should always get a result.
+        while (true) {
+            try {
+                return Objects.toString(this.t);
+            }
+            catch (ConcurrentModificationException ignored) { }
+        }
     }
 
     @Override