----- Original Message ----- > From: "David Holmes" <david.hol...@oracle.com> > To: "S" <simeon.danailov.andr...@gmail.com>, "core-libs-dev" > <core-libs-dev@openjdk.java.net> > Cc: "Andrey Loskutov" <losku...@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/lang/AbstractStringBuilder.java#L63 > > 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
