StringBuilder OOMs earlier with JRE 11 compared to JRE 8

[S A]

Hi all,

while working on 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
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