8312436: CompletableFuture never completes when 'Throwable.toString()' method throws Exception #18988

viktorklang-ora · 2024-04-28T09:54:34Z

Primarily offering this PR for discussion, as Throwables throwing exceptions on toString(), getLocalizedMessage(), or getMessage() seems like a rather unreasonable thing to do.

Nevertheless, there is some things we can do, as witnessed in this PR.

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Issue

JDK-8312436: CompletableFuture never completes when 'Throwable.toString()' method throws Exception (Bug - P4)

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Alan Bateman (@AlanBateman - Reviewer)

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Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk.git pull/18988/head

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$ git pr checkout 18988

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bridgekeeper · 2024-04-28T09:55:18Z

👋 Welcome back vklang! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2024-04-28T09:55:40Z

@viktorklang-ora This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8312436: CompletableFuture never completes when 'Throwable.toString()' method throws Exception

Reviewed-by: alanb

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 527 new commits pushed to the master branch:

9a8096f: 8330047: ASAN build error with gcc 13
6882b38: 8333590: UnmodifiableHeaders.toString() returns a value that represents empty headers
cbb6747: 8329581: Java launcher no longer prints a stack trace
789f704: 8322732: ForkJoinPool may underutilize cores in async mode
2c1b311: 8331854: ubsan: copy.hpp:218:10: runtime error: addition of unsigned offset to 0x7fc2b4024518 overflowed to 0x7fc2b4024510
765ad0e: 8331947: Preview creates checkbox for JEP-less preview feature
8e903ee: 8331896: JFR: Improve check for JDK classes
3cbdf8d: 8333554: Parallel: Remove unused PSParallelCompact::is_in
3944e67: 8312132: Add tracking of multiple address spaces in NMT
d0052c0: 8333326: Linux Alpine build fails after 8302744
... and 517 more: https://git.openjdk.org/jdk/compare/ea06129851be7bd9876685f74e35392874154179...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

openjdk · 2024-04-28T09:55:58Z

@viktorklang-ora The following label will be automatically applied to this pull request:

core-libs

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

viktorklang-ora · 2024-04-28T09:55:58Z

src/java.base/share/classes/java/util/concurrent/CompletableFuture.java

+     * String {@code "Completed normally"} or the String {@code
+     * "Completed exceptionally"}, or the String {@code "Not


These two looks like a discrepancy between spec and implementation, and it seemed safer to amend the spec rather than the implementation, as code might be relying on actual behavior rather than the spec:ed one.

@DougLea You might have some thoughts to offer on this :)

viktorklang-ora · 2024-04-28T09:58:14Z

src/java.base/share/classes/java/util/concurrent/CompletableFuture.java

@@ -2623,7 +2667,7 @@ public String toString() {
                ? "[Not completed]"
                : "[Not completed, " + count + " dependents]")
             : (((r instanceof AltResult) && ((AltResult)r).ex != null)
-                ? "[Completed exceptionally: " + ((AltResult)r).ex + "]"
+                ? "[Completed exceptionally: " + ((AltResult)r).ex.getClass().getName() + "]"


@DougLea @AlanBateman It seemed safer to switch to outputting the cause FQCN rather than wrapping in a try-catch and trying to come up with a fallback text.

The reason for amending this is for things like JShell, results are toString():ed which would mean that the current session would break if toString():ing the result throws (also further signalling that throwing on toString() seems unreasonable in general).

viktorklang-ora · 2024-04-28T09:59:16Z

test/jdk/java/util/concurrent/tck/CompletableFutureTest.java

+        // This makes sure that CompletableFuture still behaves appropriately
+        // even if thrown exceptions end up throwing exceptions from their String
+        // representations.
+        @Override public String getMessage() {


I decided to do this to make sure that all pre-existing test cases would still work even if the exception used has a misbehaving toString() (toString() transitively calls getLocalizedMessage() which in turn calls getMessage())

viktorklang-ora · 2024-04-28T10:00:17Z

src/java.base/share/classes/java/util/concurrent/CompletableFuture.java

+    static CompletionException wrapInCompletionException(Throwable t) {
+        if (t == null)
+            return new CompletionException();
+
+        String message;
+        Throwable suppressed;
+        try {
+            message = t.toString();
+            suppressed = null;
+        } catch (Throwable unknown) {
+            message = "";
+            suppressed = unknown;
+        }
+
+        final CompletionException wrapping = new CompletionException(message, t);
+
+        if (suppressed != null)
+            wrapping.addSuppressed(suppressed);
+
+        return wrapping;
+    }
+
+    static ExecutionException wrapInExecutionException(Throwable t) {
+        if (t == null)
+            return new ExecutionException();
+
+        String message;
+        Throwable suppressed;
+        try {
+            message = t.toString();
+            suppressed = null;
+        } catch (Throwable unknown) {
+            message = "";
+            suppressed = unknown;
+        }
+
+        final ExecutionException wrapping = new ExecutionException(message, t);
+
+        if (suppressed != null)
+            wrapping.addSuppressed(suppressed);
+
+        return wrapping;
+    }
+


This is the main thing—and the big question is if this approach is the best path or not.

liach · 2024-04-29T11:48:08Z

src/java.base/share/classes/java/util/concurrent/CompletableFuture.java

@@ -306,13 +306,57 @@ final boolean completeValue(T t) {
        return RESULT.compareAndSet(this, null, (t == null) ? NIL : t);
    }

+    static CompletionException wrapInCompletionException(Throwable t) {
+        if (t == null)


Is there any preexisting code path that ever passes a null? If not I don't think this check is necessary.

I opted to be more safe than sorry. Since this is on the failure-path it isn't performance critical so I think affording a null-check is fine.

mlbridge · 2024-05-10T14:42:22Z

Webrevs

00: Full (245f07a6)

viktorklang-ora · 2024-06-05T13:24:34Z

@AlanBateman Do you have a minute to review this one?

viktorklang-ora · 2024-06-05T14:39:26Z

/integrate

openjdk · 2024-06-05T14:40:06Z

Going to push as commit 326dbb1.
Since your change was applied there have been 527 commits pushed to the master branch:

9a8096f: 8330047: ASAN build error with gcc 13
6882b38: 8333590: UnmodifiableHeaders.toString() returns a value that represents empty headers
cbb6747: 8329581: Java launcher no longer prints a stack trace
789f704: 8322732: ForkJoinPool may underutilize cores in async mode
2c1b311: 8331854: ubsan: copy.hpp:218:10: runtime error: addition of unsigned offset to 0x7fc2b4024518 overflowed to 0x7fc2b4024510
765ad0e: 8331947: Preview creates checkbox for JEP-less preview feature
8e903ee: 8331896: JFR: Improve check for JDK classes
3cbdf8d: 8333554: Parallel: Remove unused PSParallelCompact::is_in
3944e67: 8312132: Add tracking of multiple address spaces in NMT
d0052c0: 8333326: Linux Alpine build fails after 8302744
... and 517 more: https://git.openjdk.org/jdk/compare/ea06129851be7bd9876685f74e35392874154179...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-06-05T14:40:14Z

@viktorklang-ora Pushed as commit 326dbb1.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

He-Pin · 2024-06-28T05:01:05Z

Will this be backported to JDK21U?

CompletableFuture should be more resilient against misbehaving except…

245f07a

…ions

viktorklang-ora commented Apr 28, 2024

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viktorklang-ora commented Apr 28, 2024

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liach reviewed Apr 29, 2024

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viktorklang-ora marked this pull request as ready for review May 10, 2024 14:38

openjdk bot added the rfr Pull request is ready for review label May 10, 2024

AlanBateman approved these changes Jun 5, 2024

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openjdk bot added the integrated Pull request has been integrated label Jun 5, 2024

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8312436: CompletableFuture never completes when 'Throwable.toString()' method throws Exception #18988

8312436: CompletableFuture never completes when 'Throwable.toString()' method throws Exception #18988

viktorklang-ora commented Apr 28, 2024 •

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He-Pin commented Jun 28, 2024

		* String {@code "Completed normally"} or the String {@code
		* "Completed exceptionally"}, or the String {@code "Not

8312436: CompletableFuture never completes when 'Throwable.toString()' method throws Exception #18988

8312436: CompletableFuture never completes when 'Throwable.toString()' method throws Exception #18988

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