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  1. JDK
  2. JDK-8216049

stringTable::intern creates redundant String when looking up existing one

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    Backports

      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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            Backport - A issue that is required to port a Bug or Feature into another product release. This issue type is generally associated with the main Bug/Feature to represent each individual release of the port. JDK-8219529 stringTable::intern creates redundant String when looking up existing one

            • P3 - Major loss of function.
            • Resolved

            Backport - A issue that is required to port a Bug or Feature into another product release. This issue type is generally associated with the main Bug/Feature to represent each individual release of the port. JDK-8219665 stringTable::intern creates redundant String when looking up existing one

            • P3 - Major loss of function.
            • Resolved

            Backport - A issue that is required to port a Bug or Feature into another product release. This issue type is generally associated with the main Bug/Feature to represent each individual release of the port. JDK-8226582 stringTable::intern creates redundant String when looking up existing one

            • P3 - Major loss of function.
            • Resolved
            relates to

            Enhancement - null JDK-8151751 Stack trace population code can (re-)use cached Strings

            • P3 - Major loss of function.
            • Closed

            Enhancement - null JDK-8208142 Fix perf regression for simple startup benchmarks in new SymbolTable

            • P4 - Minor loss of function, or other problem where easy workaround is present.
            • Resolved

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                shade Aleksey Shipilev
                redestad Claes Redestad
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