Hi,
On 2/4/08, Ian Rogers <[EMAIL PROTECTED]> wrote:
> Hi,
>
> xalan performs 1.4 million char array clones per iteration of the normal
> size DaCapo benchmark. All of the character array clones are coming from
> java.lang.String. The attached patch changes the use of char[].clone
> (which maps to java.lang.Object.clone) to a helper method that allocates
> the character array and then array copies from the source to the new
> array. On the Jikes RVM I get the following performance results from 10
> iterations of DaCapo using the large data set size:
>
> current java.lang.String using char[].clone:
> run 1: 99157ms
> run 2: 98700ms
> run 3: 97927ms
>
> patched java.lang.String using the helper routine:
> run 1: 97710ms
> run 2: 97406ms
> run 3: 96762ms
>
> The speed up is between 0.22% and 1.2%. Do people think using the helper
> is a sensible change?
>
I would like to see evidence that this is a win, or at least has no
slowdown on other VMs (i.e. it is VM independent). I think it would
be inappropriate if it was only to address implementation issues in
JikesRVM. For example, why is the helper faster than clone? Surely
all clone() should be doing is an alloc and then an arraycopy?
Rob.
> Thanks,
> Ian
>
> --- java/lang/String.java 2008-01-23 09:01:02.000000000 +0000
> +++ java/lang/String.java 2008-02-04 13:43:02.000000000 +0000
> @@ -1284,6 +1284,13 @@
> return new String(newStr, 0, newStr.length, true);
> }
>
> + private static char[] cloneCharArray(char[] src)
> + {
> + char[] copy = new char[src.length];
> + VMSystem.arraycopy(src, 0, copy, 0, src.length);
> + return copy;
> + }
> +
> /**
> * Replaces every instance of a character in this String with a new
> * character. If no replacements occur, this is returned.
> @@ -1303,7 +1310,7 @@
> break;
> if (i < 0)
> return this;
> - char[] newStr = (char[]) value.clone();
> + char[] newStr = cloneCharArray(value);
> newStr[x] = newChar;
> while (--i >= 0)
> if (value[++x] == oldChar)
> @@ -1450,7 +1457,7 @@
>
> // Now we perform the conversion. Fortunately, there are no
> multi-character
> // lowercase expansions in Unicode 3.0.0.
> - char[] newStr = (char[]) value.clone();
> + char[] newStr = cloneCharArray(value);
> do
> {
> char ch = value[x];
> @@ -1504,7 +1511,7 @@
>
> // Now we perform the conversion. Fortunately, there are no
> // multi-character lowercase expansions in Unicode 3.0.0.
> - char[] newStr = (char[]) value.clone();
> + char[] newStr = cloneCharArray(value);
> do
> {
> char ch = value[x];
> @@ -1557,7 +1564,7 @@
> i = count;
> if (expand == 0)
> {
> - char[] newStr = (char[]) value.clone();
> + char[] newStr = cloneCharArray(value);
> while (--i >= 0)
> {
> char ch = value[x];
> @@ -1642,7 +1649,7 @@
> i = count;
> if (expand == 0)
> {
> - char[] newStr = (char[]) value.clone();
> + char[] newStr = cloneCharArray(value);
> while (--i >= 0)
> {
> char ch = value[x];
> @@ -1731,7 +1738,7 @@
> public char[] toCharArray()
> {
> if (count == value.length)
> - return (char[]) value.clone();
> + return cloneCharArray(value);
>
> char[] copy = new char[count];
> VMSystem.arraycopy(value, offset, copy, 0, count);
>
>
