RFR: 8295537: Debug tracing for resolved java.lang.invoke.CallSite [v2]

[Ioi Lam]

On Tue, 25 Oct 2022 13:16:19 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   @JornVernee comments
>
> src/java.base/share/classes/java/lang/invoke/CallSite.java line 179:
> 
>> 177:         target.type();  // null check
>> 178:         this.target = target;
>> 179:         if (MethodHandleStatics.TRACE_CALLSITE) {
> 
> This doesn't seem like the right place to put this. Anyone can indirectly extend CallSite, by extending e.g. MutableCallSite, but this code seems to assume that the call is going through `MethodHandleNatives.linkCallSite`? I suggest putting any tracing around that area. Both the target method handle, and the BSM are available at that point in the code as well.
> 
> I also note that there's already a `TRACE_METHOD_LINKAGE` flag as well, which does some tracing of call site linking. Maybe that option could be enhanced instead of adding a new one?

Thanks for the suggestion! I removed the new property and just piggyback on `TRACE_METHOD_LINKAGE`. I also moved the tracing code into `MethodHandleNatives.linkCallSiteXXX`, and improved the existing code a bit to print out the line number of the call site.

Here's what it looks like now:


$ java -Djava.lang.invoke.MethodHandle.TRACE_METHOD_LINKAGE=true -cp . StrConcat
[...]
linkCallSite StrConcat.main(StrConcat.java:6) java.lang.invoke.StringConcatFactory.makeConcatWithConstants(Lookup,String,MethodType,String,Object[])CallSite/invokeStatic makeConcatWithConstants(String)String/BSA1=World
linkCallSite target class => java.lang.invoke.BoundMethodHandle$Species_LL
linkCallSite target => (String)String : invoke001_LL_L=Lambda(a0:L/SpeciesData[LL => BoundMethodHandle$Species_LL],a1:L)=>{
    t2:L=BoundMethodHandle$Species_LL.argL1(a0:L);
    t3:L=BoundMethodHandle$Species_LL.argL0(a0:L);
    t4:L=MethodHandle.invokeBasic(t3:L,a1:L,t2:L);t4:L}
& BMH=[
  0: MethodHandle = {(Object,Object)String : DMH.invokeStatic000_LLL_L=Lambda(a0:L,a1:L,a2:L)=>{
        t3:L=DirectMethodHandle.internalMemberName(a0:L);
        t4:L=MethodHandle.linkToStatic(a1:L,a2:L,t3:L);t4:L}
    & DMH.MN=java.lang.StringConcatHelper.simpleConcat(Object,Object)String/invokeStatic
  }
  1: ( World )
]
linkCallSite linkage => java.lang.invoke.Invokers$Holder.linkToTargetMethod(Object,Object)Object/invokeStatic + MethodHandle(String)String
HelloWorld

-------------

PR: https://git.openjdk.org/jdk/pull/10842