RFR: 8331987: Enhance stacktrace clarity for CompletableFuture CancellationException

[Viktor Klang]

On Mon, 13 May 2024 17:03:00 GMT, Chen Liang <liach at openjdk.org> wrote:

>> This change adds wrapping of the CancellationException produced by CompletableFuture::get() and CompletableFuture::join() to add more diagnostic information and align better with FutureTask.
>> 
>> Running the sample code from the JBS issue in JShell will produce the following:
>> 
>> 
>> jshell> java.util.concurrent.CancellationException: 
>> 	at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:392)
>> 	at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2073)
>> 	at REPL.$JShell$18.m2($JShell$18.java:10)
>> 	at REPL.$JShell$17.m1($JShell$17.java:8)
>> 	at REPL.$JShell$16B.lambda$main$0($JShell$16B.java:8)
>> 	at java.base/java.lang.Thread.run(Thread.java:1575)
>> Caused by: java.util.concurrent.CancellationException
>> 	at java.base/java.util.concurrent.CompletableFuture.cancel(CompletableFuture.java:2510)
>> 	at REPL.$JShell$16B.lambda$main$1($JShell$16B.java:11)
>> 	... 1 more
>
> src/java.base/share/classes/java/util/concurrent/CancellationException.java line 72:
> 
>> 70:      * @param cause the underlying cancellation exception
>> 71:      */
>> 72:     CancellationException(String message, CancellationException cause) {
> 
> Can we remove the message argument, which is always empty?

Good question. So what I did was to initially omit it, but then the message becomes the type of the cause, which didn't look right. Then I passed in the empty-string in the constructor, but that seemed too restrictive, since the overload is for in-package use only, I opted for some flexibility in case we want to customize the message on `get` vs `join`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19219#discussion_r1598788602