Yes that's exactly what I'm looking for as well. Sent from my phone On Jan 11, 2013 11:25 AM, "Peter Levart" <peter.lev...@gmail.com> wrote:
> On 01/11/2013 04:54 PM, Eric McCorkle wrote: > >> The webrev has been updated again. >> >> The multiple writes to parameters have been removed, and the tests have >> been expanded to look at inner classes, and to test modifiers. >> >> Please look over it again. >> > > Hello Eric, > > You still have 2 reads of volatile even in fast path. I would do it this > way: > > > private Parameter[] privateGetParameters() { > Parameter[] tmp = parameters; // one and only read > if (tmp != null) > return tmp; > > // Otherwise, go to the JVM to get them > tmp = getParameters0(); > > // If we get back nothing, then synthesize parameters > if (tmp == null) { > final int num = getParameterCount(); > tmp = new Parameter[num]; > for (int i = 0; i < num; i++) > // TODO: is there a way to synthetically derive the > // modifiers? Probably not in the general case, since > // we'd have no way of knowing about them, but there > // may be specific cases. > tmp[i] = new Parameter("arg" + i, 0, this, i); > // This avoids possible races from seeing a > // half-initialized parameters cache. > } > > parameters = tmp; > > return tmp; > } > > > Regards, Peter > > >> Test-wise, I've got a clean run on JPRT (there were some failures in >> lambda stuff, but I've been seeing that for some time now). >> >> On 01/10/13 21:47, Eric McCorkle wrote: >> >>> On 01/10/13 19:50, Vitaly Davidovich wrote: >>> >>>> Hi Eric, >>>> >>>> Parameter.equals() doesn't need null check - instanceof covers that >>>> already. >>>> >>>> Removed. >>> >>> Maybe this has been mentioned already, but personally I'm not a fan of >>>> null checks such as "if (null == x)" - I prefer the null on the right >>>> hand side, but that's just stylistic. >>>> >>> Changed. >>> >>> Perhaps I'm looking at a stale webrev but >>>> Executable.**privateGetParameters() reads and writes from/to the >>>> volatile >>>> field more than once. I think Peter already mentioned that it should >>>> use one read into a local and one write to publish the final version to >>>> the field (it can return the temp as well). >>>> >>>> You weren't. From a pure correctness standpoint, there is nothing >>> wrong >>> with what is there. getParameters0 is a constant function, and >>> parameters is writable only if null. Hence, we only every see one >>> nontrivial write to it. >>> >>> But you are right, it should probably be reduced to a single write, for >>> performance reasons (to avoid unnecessary memory barriers). Therefore, >>> I changed it. >>> >>> However, I won't be able to refresh the webrev until tomorrow. >>> >>> Thanks >>>> >>>> Sent from my phone >>>> >>>> On Jan 10, 2013 6:05 PM, "Eric McCorkle" <eric.mccor...@oracle.com >>>> <mailto:eric.mccorkle@oracle.**com <eric.mccor...@oracle.com>>> wrote: >>>> >>>> The webrev has been refreshed with the solution I describe below >>>> implemented. Please make additional comments. >>>> >>>> On 01/10/13 17:29, Eric McCorkle wrote: >>>> > Good catch there. I made the field volatile, and I also did the >>>> same >>>> > with the cache fields in Parameter. >>>> > >>>> > It is possible with what exists that you could wind up with >>>> multiple >>>> > copies of identical parameter objects in existence. It goes >>>> something >>>> > like this >>>> > >>>> > thread A sees Executable.parameters is null, goes into the VM to >>>> get them >>>> > thread B sees Executable.parameters is null, goes into the VM to >>>> get them >>>> > thread A stores to Executable.parameters >>>> > thread B stores to Executable.parameters >>>> > >>>> > Since Parameters is immutable (except for its caches, which will >>>> always >>>> > end up containing the same things), this *should* have no visible >>>> > effects, unless someone does == instead of .equals. >>>> > >>>> > This can be avoided by doing a CAS, which is more expensive >>>> execution-wise. >>>> > >>>> > My vote is to *not* do a CAS, and accept that (in extremely rare >>>> cases, >>>> > even as far as concurrency-related anomalies go), you may end up >>>> with >>>> > duplicates, and document that very well. >>>> > >>>> > Thoughts? >>>> > >>>> > On 01/10/13 16:10, Peter Levart wrote: >>>> >> Hello Eric, >>>> >> >>>> >> I have another one. Although not very likely, the reference to >>>> the same >>>> >> Method/Constructor can be shared among multiple threads. The >>>> publication >>>> >> of a parameters array should therefore be performed via a >>>> volatile write >>>> >> / volatile read, otherwise it can happen that some thread sees >>>> >> half-initialized array content. The 'parameters' field in >>>> Executable >>>> >> should be declared as volatile and there should be a single read >>>> from it >>>> >> and a single write to it in the privateGetParameters() method >>>> (you need >>>> >> a local variable to hold intermediate states)... >>>> >> >>>> >> Regards, Peter >>>> >> >>>> >> On 01/10/2013 09:42 PM, Eric McCorkle wrote: >>>> >>> Thanks to all for initial reviews; however, it appears that the >>>> version >>>> >>> you saw was somewhat stale. I've applied your comments (and >>>> some >>>> >>> changes that I'd made since the version that was posted). >>>> >>> >>>> >>> Please take a second look. >>>> >>> >>>> >>> Thanks, >>>> >>> Eric >>>> >>> >>>> >>> >>>> >>> On 01/10/13 04:19, Peter Levart wrote: >>>> >>>> Hello Eric, >>>> >>>> >>>> >>>> You must have missed my comment from the previous webrev: >>>> >>>> >>>> >>>> 292 private Parameter[] privateGetParameters() { >>>> >>>> 293 if (null != parameters) >>>> >>>> 294 return parameters.get(); >>>> >>>> >>>> >>>> If/when the 'parameters' SoftReference is cleared, the method >>>> will be >>>> >>>> returning null forever after... >>>> >>>> >>>> >>>> You should also retrieve the referent and check for it's >>>> presence before >>>> >>>> returning it: >>>> >>>> >>>> >>>> Parameter[] res; >>>> >>>> if (parameters != null && (res = parameters.get()) != null) >>>> >>>> return res; >>>> >>>> ... >>>> >>>> ... >>>> >>>> >>>> >>>> Regards, Peter >>>> >>>> >>>> >>>> On 01/09/2013 10:55 PM, Eric McCorkle wrote: >>>> >>>>> Hello, >>>> >>>>> >>>> >>>>> Please review the core reflection API implementation of >>>> parameter >>>> >>>>> reflection. This is the final component of method parameter >>>> reflection. >>>> >>>>> This was posted for review before, then delayed until the >>>> check-in for >>>> >>>>> JDK-8004728 (hotspot support for parameter reflection), which >>>> occurred >>>> >>>>> yesterday. >>>> >>>>> >>>> >>>>> Note: The check-in of JDK-8004728 was into hsx/hotspot-rt, >>>> *not* >>>> >>>>> jdk8/tl; therefore, it may be a while before the changeset >>>> makes its way >>>> >>>>> into jdk8/tl. >>>> >>>>> >>>> >>>>> Also note: since the check-in of JDK-8004727 (javac support >>>> for >>>> >>>>> parameter reflection), there has been a failure in the tests >>>> for >>>> >>>>> Pack200. This is being addressed in a fix contributed by >>>> Kumar, which I >>>> >>>>> believe has also been posted for review. >>>> >>>>> >>>> >>>>> The open webrev is here: >>>> >>>>> >>>> http://cr.openjdk.java.net/~**coleenp/JDK-8004729<http://cr.openjdk.java.net/~coleenp/JDK-8004729> >>>> >>>>> >>>> >>>>> The feature request is here: >>>> >>>>> >>>> http://bugs.sun.com/view_bug.**do?bug_id=8004729<http://bugs.sun.com/view_bug.do?bug_id=8004729> >>>> >>>>> >>>> >>>>> The latest version of the spec can be found here: >>>> >>>>> >>>> http://cr.openjdk.java.net/~**abuckley/8misc.pdf<http://cr.openjdk.java.net/~abuckley/8misc.pdf> >>>> >>>>> >>>> >>>>> >>>> >>>>> Thanks, >>>> >>>>> Eric >>>> >> >>>> >>>> >