RFR 8062116: JVMTI GetClassMethods is Slow

[Coleen Phillimore]

On 11/5/14, 6:13 PM, Jeremy Manson wrote:
>
>
> On Tue, Nov 4, 2014 at 8:56 PM, serguei.spitsyn at oracle.com 
> <mailto:serguei.spitsyn at oracle.com> <serguei.spitsyn at oracle.com 
> <mailto:serguei.spitsyn at oracle.com>> wrote:
>
>     The fix looks good in general.
>
>     src/share/vm/oops/method.cpp
>
>     1785   bool contains(Method** m) {
>     1786     if (m == NULL) return false;
>     1787     for (JNIMethodBlockNode* b = &_head; b != NULL; b = b->_next) {
>     1788       if (b->_methods <= m && m < b->_methods + b->_number_of_methods) {
>     *1789         ptrdiff_t idx = m - b->_methods;**
>     **1790         if (b->_methods + idx == m) {**
>     1791           return true;
>     1792         }*
>     1793       }
>     1794     }
>     1795     return false;  // not found
>     1796   }
>
>
>     Just noticed that the lines 1789-1792 can be replaced with one liner:
>     *        return true;*
>
>
> Ah, you have found our crappy workaround for wild pointers to 
> non-aligned places in the middle of _methods.

Can you explain this?  Why are there wild pointers?
>
>     It is because the condition *(b->_methods + idx == m)* is always
>     true.     :)
>
>     Also, should we check the condition: **m != _free_method*** ?
>     What about the following ?:
>     *        return (****m != _free_method***);*
>
>
> I don't mind adding this, if Coleen thinks those are the semantics 
> this needs.  It wasn't there before, of course.
>

The semantics weren't there before and the way this is called has 
already checked that *m != _free_method.  Would it be an improvement?  I 
don't think so.  It seems that contains() should just check that the 
Method** is contained in the methodID table.  To be more correct, 
is_method_id should check that it's not a freed methodID but the caller 
verifies this already.   So I don't think this should change.

BTW, I've run the test sets suggested by Serguei and they all passed.

Coleen

> Jeremy
>

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