help understanding the "putLongRelease" implemetation in openjdk9

[Mikael Vidstedt]

Adding back the hotspot-dev mailing list - please keep it on the cc: line.

The JIT compiler only compiles methods which are “hot” (which are being executed a lot). Before the methods are JIT compiled they are executed by the interpreter. The interpreter will *not* short-circuit the method, and will instead execute it exactly like it’s written, delegating to putLongVolatile which will take execution into unsafe.cpp/Unsafe_PutLongVolatile. Leaving the body of the method empty would mean that if the method is not JIT compiled, the interpreter would effectively execute a no-op, which of course will not have the desired effect.

Cheers,
Mikael

> On Oct 27, 2016, at 9:51 PM, 恶灵骑士 <1072213404 at qq.com> wrote:
> 
> 
> you already know that  JIT compiler handles the method 
> 'public final void putLongRelease(Object o, long offset, long x) ' differently,
> 
> why you still implemeted the method putLongRelease as
> '@HotSpotIntrinsicCandidate
> public final void putLongRelease(Object o, long offset, long x) {
>         putLongVolatile(o, offset, x);
>  }'
> 
> Why can't it  be a  empty method  like '@HotSpotIntrinsicCandidate
> public final void putLongRelease(Object o, long offset, long x) {
> 
>  }'  ?
> 
> Is method putLongRelease used somewhere else not by JIT?
> 
> 
> ------------------ 原始邮件 ------------------
> 发件人: "Mikael Vidstedt";<mikael.vidstedt at oracle.com>;
> 发送时间: 2016年10月28日(星期五) 中午12:04
> 收件人: "恶灵骑士"<1072213404 at qq.com>;
> 抄送: "hotspot-dev"<hotspot-dev at openjdk.java.net>;
> 主题: Re: help understanding the "putLongRelease" implemetation in openjdk9
> 
> 
> In jdk/src/java.base/share/classes/jdk/internal/misc/Unsafe.cpp you’ll find this:
> 
>     /** Release version of {@link #putLongVolatile(Object, long, long)} */
>     @HotSpotIntrinsicCandidate
>     public final void putLongRelease(Object o, long offset, long x) {
>         putLongVolatile(o, offset, x);
>     }
> 
> That is - in the default/interpreter case the putLongRelease method will delegate to the putLongVolatile method, and putLongVolatile in turn is in the default/interpreter case implemented in unsafe.cpp. However, the @HotSpotIntrinsicCandidate annotation is an indication that the JIT compiler handles the method differently, and if you have a look at hotspot/src/share/vm/opto/library_call.cpp you’ll find that putLongRelease, along with the other methods in the same family, get intensified and expanded during compilation using the inline_unsafe_access C++ method.
> 
> Cheers,
> Mikael
> 
> > On Oct 27, 2016, at 8:29 PM, 恶灵骑士 <1072213404 at qq.com> wrote:
> > 
> > for jdk8     according to src/share/vm/classfile/vmSymbols.hpp
> > do_intrinsic(_putOrderedLong,           sun_misc_Unsafe,        putOrderedLong_name, putOrderedLong_signature, F_RN)  
> > do_name(     putOrderedLong_name,                             "putOrderedLong")     
> > 
> > 
> > 
> > i can find  method "putOrderedLong" in src/share/vm/prims/unsafe.hpp,
> > 
> > 
> > but for jdk9  src/share/vm/classfile/vmSymbols.hpp
> > do_intrinsic(_getLongAcquire,          jdk_internal_misc_Unsafe,        getLongAcquire_name, getLong_signature,       F_R)
> > do_name(getLongAcquire_name,    "getLongAcquire")      do_name(putLongRelease_name,    "putLongRelease") 
> > 
> > 
> > i can not find  method "putLongRelease" in src/share/vm/prims/unsafe.hpp, 
> > why ?  
> > Is the method "putLongRelease"  of interpreter userd version discarded?  
> > only reserve the  implemetation of compiler used version?