RFR: 8349241: Fix the concurrent execution JVM crash of StringBuilder::append(int/long) [v4]

[Thomas Stuefe]

On Tue, 4 Feb 2025 00:59:57 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> The following code can reproduce the problem, writing out of bounds causes JVM Crash
>> 
>> 
>>    StringBuilder buf = new StringBuilder();
>>     buf.append('中');
>> 
>>     final CountDownLatch latch = new CountDownLatch(10);
>>     Runnable r = () -> {
>>         for (int i = 0; i < 10000; i++) {
>>             buf.setLength(0);
>>             buf.trimToSize();
>>             buf.append(123456789);
>>         }
>>         latch.countDown();
>>     };
>>     Thread[] threads = new Thread[10];
>>     for (int i = 0; i < threads.length; i++) {
>>         threads[i] = new Thread(r);
>>     }
>>     for (Thread t : threads) {
>>         t.start();
>>     }
>>     latch.await();
>> }
>> 
>> 
>> This problem can be avoided by using the value of ensureCapacityInternal directly.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   skip coder change

I am confused about the description. How exactly is the JVM crashed? Does the interpreter or compiled code crash?

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PR Comment: https://git.openjdk.org/jdk/pull/23427#issuecomment-2633788477