----- Original Message -----

From: "David Holmes" <david.holmes@oracle.com> To: "S" <simeon.danailov.andreev@gmail.com>, "core-libs-dev" <core-libs-dev@openjdk.java.net> Cc: "Andrey Loskutov" <loskutov@gmx.de> Sent: Vendredi 27 Août 2021 15:25:25 Subject: Re: StringBuilder OOMs earlier with JRE 11 compared to JRE 8

Hi Simeon,

Redirecting this to core-libs-dev as it is not a serviceability issue. (bcc serviceabillity-dev)

Hi Simeon, in Java 9, the String representation was changed to use less memory if the characters can be encoded in ISO Latin 1, a side effect is that StringBuilder now uses a byte[] instead of a char[], hence the maximum size being half the one it was previously.

Thanks, David

[1] https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/...

On 27/08/2021 8:53 pm, S A wrote:

...

Hi all,

while working on https://bugs.eclipse.org/bugs/show_bug.cgi?id=575641 <https://bugs.eclipse.org/bugs/show_bug.cgi?id=575641>, I noticed that StringBuilder throws an OOM "half as early" in OpenJDK 11 (and 17 early access), when compared to OpenJDK 8.

In particular, I ran the following snippet to see where the limit of appending to a StringBuilder is:

StringBuilder sb = new StringBuilder(); long n = 8L * 1024L * 1024L; for (long i = 0; i < n; ++i) { int m = 1024; for (int j = 0; j < m; ++j) { int length = sb.length(); try { sb.append((char) j); } catch (Error e) { System.out.println("Error occurred at length=" + length + " [i=" + i + ", j=" + j + "]"); throw e; }

} }

JRE 8:

Error occurred at length=2147483645 [i=2097151, j=1021] Exception in thread "main" java.lang.OutOfMemoryError: Requested array size exceeds VM limit at java.util.Arrays.copyOf(Arrays.java:3332) at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124) at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:649) at java.lang.StringBuilder.append(StringBuilder.java:202) at test.stringbuilder.TestStringbuilderOOM.main(TestStringbuilderOOM.java:13)

JRE 11:

Error occurred at length=1073741822 [i=1048575, j=1022] Exception in thread "main" java.lang.OutOfMemoryError: Requested array size exceeds VM limit at java.base/java.util.Arrays.copyOf(Arrays.java:3745) at java.base/java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:172) at java.base/java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:748) at java.base/java.lang.StringBuilder.append(StringBuilder.java:241) at TestJava11/test.stringbuilder.TestStringbuilderOOM.main(TestStringbuilderOOM.java:13)

While StringBuilder is not a good choice for holding GBs of text, I wonder that no effort is made to clamp the capacity to its limit when (I assume) it is being doubled upon array expansion.

Is this something that should be looked into or it can be safely ignored (from JDK users POV)?

Best regards, Simeon