[9] RFR (S): 8058892: FILL_ARRAYS and ARRAYS are eagely initialized in MethodHandleImpl

Peter Levart peter.levart at gmail.com
Thu Oct 2 18:33:47 UTC 2014

On 10/02/2014 06:55 PM, Vladimir Ivanov wrote:
> Small update:
> http://cr.openjdk.java.net/~vlivanov/8058892/webrev.01/
> Need to reorder initialization sequence in MHI.Lazy. Initialized 
> FILL_ARRAYS and ARRAYS are required for later MH lookups.
> Additional testing:
>   * jck (api/java_lang/invoke)
>   * jdk/java/lang/invoke, jdk/java/util/streams w/ "-ea -esa" and 
> Best regards,
> Vladimir Ivanov

Hi Vladimir,

I have a comment that does not directly pertain to the code changes (the 
initialization of arrays) but to the sub-optimal implementation of 
"fillArray" methods I noticed by the way. While it is nice to use 
varargs "makeArray" helper method with "array" methods to construct the 
array, the same strategy used with "fillWithArguments" in "fillArray" 
methods makes a redundant array that is then copied to target array and 
discarded. The redundant copying has a price. Here's a benchmark 
(Aleksey, please bear with me):

public class FillArrayTest {

     private Object
         a0 = new Object(),
         a1 = new Object(),
         a2 = new Object(),
         a3 = new Object(),
         a4 = new Object(),
         a5 = new Object(),
         a6 = new Object(),
         a7 = new Object();

     private static void fillWithArguments(Object[] a, int pos, 
Object... args) {
         System.arraycopy(args, 0, a, pos, args.length);

     private static Object[] fillArray(
         Integer pos, Object[] a,
         Object a0, Object a1, Object a2, Object a3,
         Object a4, Object a5, Object a6, Object a7
     ) {
         fillWithArguments(a, pos, a0, a1, a2, a3, a4, a5, a6, a7);
         return a;

     private static Object[] fillArrayAlt(
         Integer pos, Object[] a,
         Object a0, Object a1, Object a2, Object a3,
         Object a4, Object a5, Object a6, Object a7
     ) {
         int i = pos;
         a[i++] = a0;
         a[i++] = a1;
         a[i++] = a2;
         a[i++] = a3;
         a[i++] = a4;
         a[i++] = a5;
         a[i++] = a6;
         a[i++] = a7;
         return a;

     public Object[] fillArray() {
         return fillArray(0, new Object[8], a0, a1, a2, a3, a4, a5, a6, a7);

     public Object[] fillArrayAlt() {
         return fillArrayAlt(0, new Object[8], a0, a1, a2, a3, a4, a5, 
a6, a7);

The results on my i7 with JMH arguments "-i 8 -wi 5 -f 1 -gc true":

Benchmark                          Mode   Samples        Score Score 
error    Units
j.t.FillArrayTest.fillArray       thrpt         8 48601447.674 
5414853.634    ops/s
j.t.FillArrayTest.fillArrayAlt    thrpt         8 90044973.732 
8713725.735    ops/s

So fillArrayAlt is nearly twice as fast...

Regards, Peter

> On 10/2/14, 7:52 PM, Vladimir Ivanov wrote:
>> http://cr.openjdk.java.net/~vlivanov/8058892/webrev.00/
>> https://bugs.openjdk.java.net/browse/JDK-8058892
>> Core j.l.i classes are preloaded during VM startup in order to avoid
>> possible deadlock when accessing JSR292-related functionality from
>> multiple threads. After LF sharing-related changes, FILL_ARRAYS and
>> ARRAYS are initialized too early. It affects startup time & footprint of
>> applications that don't use JSR292.
>> The fix is to move these fields into MHI.Lazy class, thus delaying their
>> initialization to the first usage of JSR292 API.
>> Testing: failing test, manual (measured HelloWorld app startup time;
>> compared -XX:+PrintCompilation logs)
>> Best regards,
>> Vladimir Ivanov
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