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From "Henri Yandell (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LANG-877) Performance improvements for StringEscapeUtils
Date Mon, 21 Oct 2013 19:55:44 GMT

     [ https://issues.apache.org/jira/browse/LANG-877?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Henri Yandell updated LANG-877:
-------------------------------

    Fix Version/s: Patch Needed

> Performance improvements for StringEscapeUtils
> ----------------------------------------------
>
>                 Key: LANG-877
>                 URL: https://issues.apache.org/jira/browse/LANG-877
>             Project: Commons Lang
>          Issue Type: Improvement
>          Components: lang.text.translate.*
>    Affects Versions: 3.1
>            Reporter: Henri Yandell
>             Fix For: Patch Needed
>
>
> An email on the list from Lawrence Angrave:
> Hi,
> Some comments that are relevant to  Apache3 UnicodeEscaper and Apache2's StringEscapeUtils.java
> Summary-
>  * I noticed the current Apache code creates three String objects each
>    time it writes a unicode hexadecimal  value.
>  * Apache3 can also create a char[] array per character translation
>    (but I do not include a fix for that)
>  * This is a easy-to-fix performance bottleneck when writing many
>    non-ascii characters.
>  * The logic to test for unicode values of different magnitudes can
>    also be simplified.
>  * Benchmark and code fixes for Apache2 and Apache 3 are included. I do
>    not have time to become an Apache maintainer. use or ignore at your
>    choice.
>  * I'm not interested in being a developer for Commons Lang  Use it or
>    not  - that's a choice for Commons Lang developers.
> A simple fix more than doubles the string escape speed (40 ms v 100ms to translate all
unicode characters) for Apache3.
> The older Apache2-style implementation can now translate all unicode characters in 8ms.
> The existing Apache3/Apache2 write unicode hex values like this-
>         if (codepoint > 0xfff) {
>                 out.write("\\u" + hex(codepoint));
>             } else if (codepoint > 0xff) {
>                 out.write("\\u0" + hex(codepoint));
>             } else if (codepoint > 0xf) {
>                 out.write("\\u00" + hex(codepoint));
>             } else {
>                 out.write("\\u000" + hex(codepoint));
>             }
> The hex() function,
> //hex(): return Integer.toHexString(codepoint).toUpperCase(Locale.ENGLISH);
> also creates two string objects, so we have 3 objects per unicode hex value.
> FIX:
> The padding logic can be simplified and per-character object creation can be eliminated
by writing hex digits directly
>             out.write("\\u");
>             out.write(HEX_DIGIT[(codepoint >> 12) & 15]);
>             out.write(HEX_DIGIT[(codepoint >> 8) & 15]);
>             out.write(HEX_DIGIT[(codepoint >> 4) & 15]);
>             out.write(HEX_DIGIT[(codepoint) & 15]);
> where  HEX_DIGIT  is
> public static final char[] HEX_DIGIT = "0123456789ABCDEF".toCharArray();
> I believe this is safe for all Locales.
> When benchmarked it was disconcerting that Apache3 is still five times slower (40ms instead
of 8ms) than my rewritten Apache2 version (included below).
> My guess is that there are other unnecessary per-character object creation issues still
lurking Here's one example -
> CharSequenceTranslator.translate(CharSequence input, Writer out) :
>        char[] c = *Character.toChars*(Character.codePointAt(input, pos))
> For better performance this should use toChars(int codePoint,  char[] dst, int dstIndex)
, which can re-use the dst char array
> The benchmark, my version of a  Apache2-style escapeJavaStyleString implementation and
the code fix for UnicodeEscaper.java  are included below.
> I hope this email does not go into a blackhole... Feel free to forward it to the relevant
maintainers.
> Regards,
> Lawrence.
>     public static final char[] HEX_DIGIT = "0123456789ABCDEF".toCharArray();
>     public static final char[] CONTROL_CHARS; // non-zero entries for special case control
characters
>     static {
>         CONTROL_CHARS = new char[32];
>         CONTROL_CHARS['\b'] = 'b';
>         CONTROL_CHARS['\n'] = 'n';
>         CONTROL_CHARS['\t'] = 't';
>         CONTROL_CHARS['\f'] = 'f';
>         CONTROL_CHARS['\r'] = 'r';
>     }
>     public static void  escapeJavaStyleString(Writer out, String s, boolean escapeSingleQuote)
throws IOException {
> // Apache2 makes the following checks, so we will too-
>     if(out==null) throw new IllegalArgumentException("The Writer must not be null");
>         if(s == null) return;
>         final int len = s.length();
>         for(int i =0; i < len;i++)
>             escapeChar(out,s.charAt(i), escapeSingleQuote);
>     }
>     public static void escapeChar(Writer out, char c, boolean escapeSingleQuote)
>             throws IOException {
>         // Most common case
>         if (c >= 32 && c < 127) {
>             if (c == '\\' || c == '"' || (c == '\'' && escapeSingleQuote))
>                 out.write('\\');
>             out.write(c);
>             return;
>         }
>         out.write('\\');
>         if (c < 32 && CONTROL_CHARS[c] != 0) {
>             out.write(CONTROL_CHARS[c]);
>             return;
>         }
>         // Fast 4 digit uppercase hexadecimal without object creation
>         out.write('u');
>         out.write(HEX_DIGIT[(c >> 12) & 15]);
>         out.write(HEX_DIGIT[(c >> 8) & 15]);
>         out.write(HEX_DIGIT[(c >> 4) & 15]);
>         out.write(HEX_DIGIT[(c) & 15]);
>     }
> FYI The benchmark test just writes all possible unicode characters into a null writer:
>             Writer nullWriter = new Writer() {
>             public void write(String s) {
>             };
>             public void write(int c) {
>             }
>             public void close() throws IOException {
>             }
>             public void flush() throws IOException {
>             }
>             public void write(char[] cbuf, int off, int len) throws IOException {
>             }
>         };
>         StringBuilder sb = new StringBuilder(0x10000);
>         for (int i = 0; i <= 0xffff; i++)
>             sb.append((char) i);
>         String allChars = sb.toString();
>         long t1 = System.currentTimeMillis();
>         StringEscaper.escapeJavaStyleString(nullWriter, allChars, true);
>         long t2 = System.currentTimeMillis();
>         System.out.println(t2 - t1);
>         long t3 = System.currentTimeMillis();
>         CharSequenceTranslator translator = StringEscapeUtils.ESCAPE_JAVA;
>         translator.translate(allChars, nullWriter);
>         long t4 = System.currentTimeMillis();
>         System.out.println(t4 - t3);
> The modification to Apache3 UnicodeEscaper :
>         if (codepoint > 0xffff) {
>             // TODO: Figure out what to do. Output as two Unicodes?
>             // Does this make this a Java-specific output class?
>             out.write("\\u" + hex(codepoint));
>         } else if (1 == 0) { //*OLD SLOW CODE* (can be removed)
> *if (codepoint > 0xfff) {
>                 out.write("\\u" + hex(codepoint));
>             } else if (codepoint > 0xff) {
>                 out.write("\\u0" + hex(codepoint));
>             } else if (codepoint > 0xf) {
>                 out.write("\\u00" + hex(codepoint));
>             } else {
>                 out.write("\\u000" + hex(codepoint));
>             }*
>         } else { // *NEW FAST CODE*
> *            out.write("\\u");
>             out.write(HEX_DIGIT[(codepoint >> 12) & 15]);
>             out.write(HEX_DIGIT[(codepoint >> 8) & 15]);
>             out.write(HEX_DIGIT[(codepoint >> 4) & 15]);
>             out.write(HEX_DIGIT[(codepoint) & 15]);*
>         }
> *and add    public static final char[] HEX_DIGIT = "0123456789ABCDEF".toCharArray();**
> *
> ps.
> The home page for Commons lang
> http://commons.apache.org/proper/commons-lang/)
>  has the following 404 link on the left
>     Contributing Patches
> http://commons.apache.org/proper/patches.html
> (I believe the 'proper' is unnecessary)



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