VarHandle does provide suitable (and better) replacements for the various Unsafe.get/putXXX methods. But, U.objectFieldOffset() is the only (easy?) Java way to inspect the layout of a class; e.g. say you apply a hacky class-hierarchy based cacheline padding to a field, and then want to assert that it got placed at the expected offset. I suppose Panama may yield a better solution here, but I'm not aware of any VarHandle APIs to replicate this usecase.
On Wed, Jun 19, 2019 at 10:59 AM Gil Tene <g...@azul.com> wrote: > Use VarHandle. It is there and it works. It allows you to replace > Unsafe.objectFildOffset with a better, safer way to do the same thing you > would be doing with the information that Unsafe.objectFildOffset > provides, but without ever giving you the (potentially incorrect and unsafe > to use) information about the "offset" of a field within an object. It > allows the manipulation field contents in pretty much any useful way that > having the offset would allow you to do with Unsafe.getX(object, offset) or > Unsafe.putX(object, offset), but without providing with unsafe means that > will break things (like e.g. writing a long to a reference field, or > overflowing an int with a long write). > > On Wednesday, June 19, 2019 at 7:04:26 AM UTC-7, xiaobai andrew wrote: >> >> thank for you reply，i look for some api just like VarHandle, which i can >> replace Unsafe.objectFildOffset without requires jdk.unsupported . >> any good idea? >> >> >> Gil Tene <g...@azul.com> 于2019年6月18日周二 下午11:43写道： >> >>> Out of curiosity: What do you use Unsafe.objectFieldOffset for that >>> VarHandle is lacking functionality for? >>> >>> It is useful to gather use cases not covered by VarHandle so that we can >>> propose additional capabilities there (preparing for a world with no Unsafe >>> in it). Can you share an example of code? >>> >>> As to your question: I assume it is Unsafe as a whole you are having >>> issues with, and not just Unsafe.objectFieldOffset, is that correct? You >>> can find examples of how to use Unsafe in a post-java-8 world e.g. here: >>> http://gregluck.com/blog/archives/2017/03/using-sun-misc-unsafe-in-java-9/ >>> >>> On Tuesday, June 18, 2019 at 5:48:14 AM UTC-7, xiaobai andrew wrote: >>>> >>>> i usr Unsafe.objectFieldOffset in jdk 8 ,but when i want to update jdk >>>> to 11, the idea compile error , it cannot found the symbol Unsafe. >>>> i have try to find VarHandle api,but it did not >>>> support Unsafe.objectFieldOffset >>>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "mechanical-sympathy" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to mechanical-sympathy+unsubscr...@googlegroups.com. >>> To view this discussion on the web, visit >>> https://groups.google.com/d/msgid/mechanical-sympathy/fd3d12a2-5f1d-4795-9e58-28723b8f02d7%40googlegroups.com >>> <https://groups.google.com/d/msgid/mechanical-sympathy/fd3d12a2-5f1d-4795-9e58-28723b8f02d7%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> For more options, visit https://groups.google.com/d/optout. >>> >> -- > You received this message because you are subscribed to the Google Groups > "mechanical-sympathy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to mechanical-sympathy+unsubscr...@googlegroups.com. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/mechanical-sympathy/d628940f-7e88-4456-abbc-3377633f4e74%40googlegroups.com > <https://groups.google.com/d/msgid/mechanical-sympathy/d628940f-7e88-4456-abbc-3377633f4e74%40googlegroups.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "mechanical-sympathy" group. To unsubscribe from this group and stop receiving emails from it, send an email to mechanical-sympathy+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/mechanical-sympathy/CAHjP37H9vDWY3rQF-2XAPnVdr9C1VrEcRWtN3E%3D71NVSkTxY2g%40mail.gmail.com.
