Review request JDK-8004729: Parameter Reflection API (original) (raw)

Vitaly Davidovich vitalyd at gmail.com
Fri Jan 11 16:54:05 UTC 2013

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.levart at 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.mccorkle at oracle.com_ _<mailto:eric.mccorkle at oracle.**com <eric.mccorkle at 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/viewbug.**do?bugid=8004729<http://bugs.sun.com/viewbug.do?bugid=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 >>

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