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From "Maurice Nicholson (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FLEX-33273) CSSCondition.matchesStyleClient() is slow and creates excessive garbage
Date Tue, 20 Nov 2012 20:50:59 GMT
Maurice Nicholson created FLEX-33273:
----------------------------------------

             Summary: CSSCondition.matchesStyleClient() is slow and creates excessive garbage
                 Key: FLEX-33273
                 URL: https://issues.apache.org/jira/browse/FLEX-33273
             Project: Apache Flex
          Issue Type: Improvement
          Components: Styles
    Affects Versions: Adobe Flex SDK 4.1 (Release), Adobe Flex SDK 4.5 (Release), Adobe Flex
SDK 4.5.1 (Release), Adobe Flex SDK 4.6 (Release)
            Reporter: Maurice Nicholson


CSSCondition.matchesStyleClient() is called *very* frequently during layout of components
in many different scenarios.

I've done a lot of profiling of Flex apps and it comes up again and again.

The current implementation is slow and creates unnecessary garbage (which slows down the runtime
further, since it needs to collect the garbage instead of doing more useful things).

Here is the current implementation:

{code}
    public function matchesStyleClient(object:IAdvancedStyleClient):Boolean
    {
        var match:Boolean = false;

        if (kind == CSSConditionKind.CLASS)
        {
            if (object.styleName != null && object.styleName is String)
            {
                // Look for a match in a potential list of styleNames 
                var styleNames:Array = object.styleName.split(/\s+/);
                for (var i:uint = 0; i < styleNames.length; i++)
                {
                    if (styleNames[i] == value)
                    {
                        match = true;
                        break;
                    }
                }
            }
        }
        else if (kind == CSSConditionKind.ID)
        {
            if (object.id == value)
                match = true;
        }
        else if (kind == CSSConditionKind.PSEUDO)
        {
            if (object.matchesCSSState(value))
                match = true;
        }

        return match;
    }
{code}

Here is what I suggest instead:

{code}
    public function matchesStyleClient(object:IAdvancedStyleClient):Boolean
    {
        var match:Boolean = false;

        if (kind == CSSConditionKind.CLASS)
        {
            const styleName:String = object.styleName as String;
            if (styleName)
            {
                // Look for a match in a potential list of styleNames 
                FIND:
                {
                    var index:int = styleName.indexOf(value);
                    if (index == -1)
                    {
                        break FIND;
                    }
                    if (index != 0 && styleName.charAt(index - 1) != ' ')
                    {
                        break FIND;
                    }
                    const next:int = index + value.length;
                    if (next != styleName.length && styleName.charAt(next) != ' ')
                    {
                        break FIND;
                    }
                    match = true;
                }
            }
        }
        else if (kind == CSSConditionKind.ID)
        {
            if (object.id == value)
                match = true;
        }
        else if (kind == CSSConditionKind.PSEUDO)
        {
            if (object.matchesCSSState(value))
                match = true;
        }

        return match;
    }
{code}

There are obviously more concise ways to express this code, but the above seems to match the
current style more or less.

Here is the output from a benchmark I created using Grant Skinner's PerformanceTest v2 Beta,
comparing the current version and the suggested version:

{noformat}
Comparing speed of matching a string in space delimited string. 1000000 loops.

Test                                                           Old ms   New ms Speedup  Old
mem  New mem  Change

matchesStyleClient(styleName: "foo", value: "foo")            1006.00   181.00   -82.0   123.00
    0.00  -100.0
matchesStyleClient(styleName: "foo bar", value: "foo")        2107.00   206.80   -90.2   115.00
    0.00  -100.0
matchesStyleClient(styleName: "bar foo", value: "foo")        2099.80   232.30   -88.9   117.00
    0.00  -100.0
matchesStyleClient(styleName: "baz foo bar", value: "foo")    3193.80   251.30   -92.1   119.00
    0.00  -100.0
matchesStyleClient(styleName: "foobar", value: "foo")         1169.50   192.00   -83.6   112.00
    0.00  -100.0
matchesStyleClient(styleName: "foofoo bar", value: "foo")     2273.80   191.30   -91.6   116.00
    0.00  -100.0
matchesStyleClient(styleName: "fo", value: "foo")              918.80   141.00   -84.7   108.00
    0.00  -100.0
matchesStyleClient(styleName: "fooo", value: "foo")           1052.80   192.00   -81.8   108.00
    0.00  -100.0
matchesStyleClient(styleName: "2foo bar", value: "foo")       2149.50   205.30   -90.4   116.00
    0.00  -100.0
matchesStyleClient(styleName: "foo2 bar", value: "foo")       3849.50   190.80   -95.0   111.00
    0.00  -100.0
matchesStyleClient(styleName: "", value: "foo")               1801.80   141.00   -92.2   132.00
    0.00  -100.0
{noformat}

As you can see, the new version doesn't create garbage, and is at least 80% faster in the
above test cases.

I would be happy to contribute a patch and a FlexUnit test, but I haven't seen any existing
FlexUnit tests in the current source tree, so not sure where to put it.

Otherwise Mustella seems like a beast to get to know and run, so I will need some guidance
as to what to do if you require new Mustella tests.

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