JDK-8216049 : stringTable::intern creates redundant String when looking up existing one
- Type: Bug
- Component: hotspot
- Sub-Component: runtime
- Affected Version: 11,12
- Priority: P3
- Status: Resolved
- Resolution: Fixed
- Submitted: 2019-01-03
- Updated: 2019-09-09
- Resolved: 2019-02-16
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To download the current JDK release, click here.
| JDK 11 | JDK 12 | JDK 13 |
|---|---|---|
| 11.0.3Fixed | 12.0.2Fixed | 13 b09Fixed  |
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Description
After JDK-8195097 in stringTable::intern the pre-insert lookup is done using a new String oop rather than the jchar* + len, which adds overhead in places like java_lang_StackTraceElement::fill_in - see https://stackoverflow.com/a/54015664/2397895
The following naive patch speeds up microbenchmarks throwing and consuming stack traces by 1.33x on my machine:
diff -r d3e199e30cfb src/hotspot/share/classfile/stringTable.cpp
--- a/src/hotspot/share/classfile/stringTable.cpp Thu Jan 03 02:26:42 2019 +0100
+++ b/src/hotspot/share/classfile/stringTable.cpp Thu Jan 03 10:29:24 2019 +0100
@@ -334,6 +334,10 @@
if (StringTable::_alt_hash) {
hash = hash_string(name, len, true);
}
+ found_string = StringTable::the_table()->do_lookup(name, len, hash);
+ if (found_string != NULL) {
+ return found_string;
+ }
return StringTable::the_table()->do_intern(string_or_null_h, name, len,
hash, CHECK_NULL);
}
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