Goal

Improve start-up time by storing pre-generated LambdaForm handlers in an application-specific CDS archive.

Background

In JDK-8086045 Improve the java.lang.invoke first initialization costs, the JDK can reduce the number of dynamically generated LambdaForm classes. Here's an example:

# Do this in your JDK build directory.
# The exploded JDK build:
$ jdk/bin/javac -J-verbose ~/tmp/HelloWorld.java | grep LambdaForm | grep __JVM_LookupDefineClass__ 
[0.142s][info][class,load] java.lang.invoke.LambdaForm$MH/0x0000000800066c40 source: __JVM_LookupDefineClass__
[0.143s][info][class,load] java.lang.invoke.LambdaForm$DMH/0x0000000800066040 source: __JVM_LookupDefineClass__
[0.143s][info][class,load] java.lang.invoke.LambdaForm$MH/0x0000000800066440 source: __JVM_LookupDefineClass__
[snip]

$ jdk/bin/javac -J-verbose ~/tmp/HelloWorld.java | grep LambdaForm | grep __JVM_LookupDefineClass__ | wc
    102     408   11400


# The final JDK image: 
$ images/jdk/bin/javac -J-verbose ~/tmp/HelloWorld.java | grep LambdaForm | grep __JVM_LookupDefineClass__ |  wc
     34     136    3800

Here's the difference between the exploded build and the final image:

$ jdk/bin/javap 'java.lang.invoke.DirectMethodHandle$Holder'
Compiled from "DirectMethodHandle.java"
final class java.lang.invoke.DirectMethodHandle$Holder {
  final java.lang.invoke.DirectMethodHandle this$0;
  java.lang.invoke.DirectMethodHandle$Holder(java.lang.invoke.DirectMethodHandle);
}


$ images/jdk/bin/javap 'java.lang.invoke.DirectMethodHandle$Holder'
Compiled from "DirectMethodHandle$Holder"
final class java.lang.invoke.DirectMethodHandle$Holder {
  static int invokeInterface(java.lang.Object, java.lang.Object, java.lang.Object);
  static java.lang.Object invokeSpecial(java.lang.Object, java.lang.Object, java.lang.Object, int);
  static java.lang.Object invokeSpecial(java.lang.Object, java.lang.Object, java.lang.Object, long);
  [~150 more lines ...]
}

The JDK image's version of the java.lang.invoke.DirectMethodHandle$Holder class is generated here in GenerateJLIClassesPlugin.java. This plugin is executed when we generate the file images/jdk/lib/modules.

private static final String DIRECT_HOLDER = "java/lang/invoke/DirectMethodHandle$Holder";
...
 byte[] bytes = JLIA.generateDirectMethodHandleHolderClassBytes(
                    DIRECT_HOLDER, directMethodTypes, dmhTypes);

The input of generateDirectMethodHandleHolderClassBytes comes from the default_jli_trace.txt file that is generated in GenerateLinkOptData.gmk:

	$(FIXPATH) $(INTERIM_IMAGE_DIR)/bin/java -XX:DumpLoadedClassList=$@.raw.2 \
	    -XX:SharedClassListFile=$@.interim -XX:SharedArchiveFile=$@.jsa \
	    -Djava.lang.invoke.MethodHandle.TRACE_RESOLVE=true \
	    -Duser.language=en -Duser.country=US \
	    --module-path $(SUPPORT_OUTPUTDIR)/classlist.jar \
	    -cp $(SUPPORT_OUTPUTDIR)/classlist.jar \
	    build.tools.classlist.HelloClasslist \
	    2> $(LINK_OPT_DIR)/stderr > $(JLI_TRACE_FILE)

Here's how roughly the contents of default_jli_trace.txt correspond to the generated methods in DirectMethodHandle$Holder

$ grep invokeSpecialIFC ./support/link_opt/default_jli_trace.txt
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecialIFC L3I_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecialIFC LLI_I (fail)

$ images/jdk/bin/javap  'java.lang.invoke.DirectMethodHandle$Holder' | grep invokeSpecialIFC
  static int invokeSpecialIFC(java.lang.Object, java.lang.Object, java.lang.Object, int);
  static int invokeSpecialIFC(java.lang.Object, java.lang.Object, int);

The methods in DirectMethodHandle$Holder are used in InvokerBytecodeGenerator.java when compiling for LambdaForms:

    private static MemberName lookupPregenerated(LambdaForm form, MethodType invokerType) {
        if (form.customized != null) {
            // No pre-generated version for customized LF
            return null;
        }
        String name = form.kind.methodName; 
        switch (form.kind) {
            [......]
            case DIRECT_INVOKE_INTERFACE:   // fall-through
            case DIRECT_INVOKE_SPECIAL:     // fall-through
            case DIRECT_INVOKE_SPECIAL_IFC: // fall-through
            case DIRECT_INVOKE_STATIC:      // fall-through
            case DIRECT_INVOKE_STATIC_INIT: // fall-through
            case DIRECT_INVOKE_VIRTUAL:     return resolveFrom(name, invokerType, DirectMethodHandle.Holder.class);
        }
        return null;

Estimated Benefits

The expected benefits will be application specific. Here's an experiment with Javac (I modified the JDK makefile to invoke com.sun.tools.javac.Main while generating default_jli_trace.txt).

Results of " perf stat -r 50 bin/javac -J-Xshare:on -J-XX:SharedArchiveFile=javac2.jsa Bench_HelloWorld.java "
   1:   2239149872  2203293903 (-35855969)      ----     375.580   367.190 ( -8.390)      ----  
   2:   2245304165  2198900711 (-46403454)      -----    375.350   366.910 ( -8.440)      ----  
   3:   2242558895  2205167765 (-37391130)      ----     376.720   366.480 (-10.240)      ----- 
   4:   2246851428  2198990987 (-47860441)      -----    375.119   367.010 ( -8.109)      ----  
   5:   2238549008  2202480450 (-36068558)      ----     374.100   367.600 ( -6.500)      ---   
   6:   2240816859  2200725384 (-40091475)      ----     375.743   366.880 ( -8.863)      ----  
   7:   2243272464  2199639926 (-43632538)      -----    374.296   365.990 ( -8.306)      ----  
   8:   2239650882  2203211291 (-36439591)      ----     375.315   365.520 ( -9.795)      ----- 
   9:   2242434935  2202380291 (-40054644)      ----     376.052   367.305 ( -8.747)      ----  
  10:   2238725993  2201342398 (-37383595)      ----     375.478   366.743 ( -8.735)      ----  
============================================================
        2241729810  2201612439 (-40117371)      ----     375.375   366.762 ( -8.612)      ----  
instr delta =    -40117371    -1.7896%
time  delta =       -8.612 ms -2.2943%

Why do it in CDS

We cannot store all possible LambdaForm handlers in the standard JDK image – we cannot enumerate all possible forms that may be used by all possible apps.
We could also do this as part of jlink, when creating a custom JDK image. However, some users may not want to create a new JDK image.
- Also, there's currently no work-flow to include profiling data when building a custom JDK image (although this can be changed, probably as part of Project Leyden)
CDS dynamic dump can be used without generating profiling data in a separate step, so the usability is better.

CDS Design

Overally, we want to modify lookupPregenerated() to something like:

    case xxxxxx: return resolveFrom(name, invokerType, directMethodHandleHolders);


Class[] directMethodHandleHolders = {
    DirectMethodHandle.Holder.class, // the one in jdk/lib/modules
    Class.forName("java/lang/invoke/DirectMethodHandle$CDSHolder1"), // if available, from CDS static archive
    Class.forName("java/lang/invoke/DirectMethodHandle$CDSHolder2"), // if available, from CDS static archive
};

During CDS dump (static or dynamic), we will generate the CDSHolder1 and CDSHolder2 classes according to the program's execution profile.

Static Dump

During the trial run (with -XX:DumpLoadedClassList=classlist), we can save the list of LambdaForm handlers using a special syntax like:

# regular class specifier
java/lang/Object
# LambdaForm specifier (syntax TBD, but probably following the output of
# -Djava.lang.invoke.MethodHandle.TRACE_RESOLVE=true
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecialIFC L3I_I
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecialIFC LLI_I
....


#The output of  -Djava.lang.invoke.MethodHandle.TRACE_RESOLVE=true (javac HelloWorld.java):
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L7_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LL_I (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L8_L (success)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder invokeExact_MT L8_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L3_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L4_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder getReference LL_L (success)
[LF_RESOLVE] java.lang.invoke.LambdaForm$Holder identity_L LL_L (success)
[LF_RESOLVE] java.lang.invoke.LambdaForm$Holder zero_L L_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial LL_L (success)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder linkToTargetMethod L_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L3_I (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder newInvokeSpecial LL_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L3_L (success)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder linkToTargetMethod LL_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeVirtual LL_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder newInvokeSpecial L_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeInterface L3_I (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LL_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial LL_I (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LI_I (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder newInvokeSpecial L3_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L4_L (success)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder linkToTargetMethod L3_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder newInvokeSpecial L4_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L5_L (success)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder linkToTargetMethod L4_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L3_V (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L4IIL_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder newInvokeSpecial L4II_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L5II_L (fail)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder linkToTargetMethod L3IIL_L (fail)
[LF_RESOLVE] java.lang.invoke.DelegatingMethodHandle$Holder delegate L3_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L4_V (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeVirtual L3_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeInterface L3_V (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L6_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L7_L (success)
[LF_RESOLVE] java.lang.invoke.DelegatingMethodHandle$Holder delegate L6_L (success)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder invokeExact_MT L7_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LLJ_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L3J_L (success)
[LF_RESOLVE] java.lang.invoke.DelegatingMethodHandle$Holder reinvoke_L LLJ_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LJLIL_J (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial LLJLIL_J (success)
[LF_RESOLVE] java.lang.invoke.DelegatingMethodHandle$Holder reinvoke_L LJLIL_J (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L5_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial LLJLI_J (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LJ_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial LLJ_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LJI_J (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial LLJI_J (success)
[LF_RESOLVE] java.lang.invoke.DelegatingMethodHandle$Holder reinvoke_L LJI_J (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L4J_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder getLong LL_J (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial LLI_J (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial LLI_L (success)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder linkToTargetMethod IL_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecialIFC LLI_I (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStaticInit LL_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeVirtual LL_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStaticInit LL_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder newInvokeSpecial L5_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L6_L (success)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder linkToTargetMethod L5_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder newInvokeSpecial L6_L (fail)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder linkToTargetMethod L6_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeVirtual L3_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeInterface LL_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStaticInit L_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LII_I (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder newInvokeSpecial LI_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LI3_I (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder newInvokeSpecial LII_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial LLII_L (success)
[LF_RESOLVE] java.lang.invoke.Invokers$Holder linkToTargetMethod IIL_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeVirtual L3_V (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L4_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeVirtual L3II_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeVirtual LLI_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L3II_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L6_V (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L5_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LL_V (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LLII_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeSpecial L3_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeInterface LL_L (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L_V (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic LI_L (success)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L4_I (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeVirtual LL_V (fail)
[LF_RESOLVE] java.lang.invoke.DirectMethodHandle$Holder invokeStatic L3_V (fail)


total is 93.
But with LambdaForm only 2:
[LF_RESOLVE] java.lang.invoke.LambdaForm$Holder identity_L LL_L (success)
[LF_RESOLVE] java.lang.invoke.LambdaForm$Holder zero_L L_L (success)


# for LambdaForm:
# javac -J-verbose HelloWorld.java | grep grep LambdaForm | grep __JVM_LookupDefineClass__
# total is 36.

We collect all the LF_RESOLVE lines when parsing the classlist. At the end of the static dump, we invoke generateDirectMethodHandleHolderClassBytes to generate the DirectMethodHandle$CDSHolder1 class (as well as other holder classes that are currently generated by GenerateJLIClassesPlugin.java.)

Details TBD ....

Dynamic Dump

TBD.

JDK-8247536 Support pre-generated MethodHandle LambdaForms in CDS