[LANG-877] Performance improvements for StringEscapeUtils

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.1
• Fix Version/s: 3.4
• Component/s: lang.text.translate.*
• Labels: github
• Assignee: Benedikt Ritter
• Reporter: Henri Yandell
• Created: 08/Mar/13 23:24
• Updated: 06/Apr/15 17:28
• Resolved: 13/Mar/15 18:19

Description

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();**
*

Issue Links

• relates to: LANG-935 Possible performance improvement on string escape functions