RFR: 8163369: Enable generating DMH classes at link time

[Aleksey Shipilev]

On 08/08/2016 02:46 PM, Claes Redestad wrote:
> Hi,
> 
> please review this change to add the ability to generate
> DirectMethodHandles to the --generate-jli-classes jlink plugin.
> 
> The implementation generates all the specified DMHs as methods into a
> single class, java.lang.invoke.DirectMethodHandle$DMH. At runtime when a
> DMH's LF is set up, we speculatively resolve the member from this class
> instead of generating and loading the bytecode as a distinct anonymous
> class. This avoids loading a potentially large number of anonymous
> classes at runtime, and also enables other startup optimizations such as
> allowing CDS to see and dump this class to the shared archive.
> 
> webrev: http://cr.openjdk.java.net/~redestad/8163369/webrev.01/

DirectMethodHandle:

 * DMH placeholder class might better be called
DirectMethodHandle.Holder, or something else that clearly spells out the
intent?


InvokerBytecodeGenerator:

 * Both generateNamedFunctionInvokerImpl() and
generateLambdaFormInterpreterEntryPointBytes() have methodEpilog() call,
but no methodPrologue()? classFilePrologue() used to do the prologue.

GenerateJLIClassesPlugin:

 * Do we actually need this block in this form?

       // DirectMethodHandles
       // Enable by default
       boolean dmhEnabled = true;
       if (mainArgument != null) {
           Set<String> args = Arrays.stream(mainArgument.split(","))
                   .collect(Collectors.toSet());
           if (!args.contains(DMH_PARAM)) {
               dmhEnabled = false;
           }
       }

 seems equivalent to a simpler:

       boolean dmhEnabled = true;
       if (mainArgument != null) {
           List<String> args = Arrays.asList(mainArgument.split(","));
           if (!args.contains(DMH_PARAM)) {
               dmhEnabled = false;
           }
        }

 You can even split the mainArgument once and reuse throughout configure()?

 * This block does not check the first argument as the comment suggests,
only checks the second group:

    String[] typeParts = type.split("_");
    if (typeParts.length != 2 || typeParts[1].length() != 1
        || "LJIFDV".indexOf(typeParts[1].charAt(0)) == -1) {
       throw new PluginException(
             "Method type signature must be of form [LJIFD]*_[LJIFDV]");
    }

 * primitiveType('Z') would throw a misleading "Not a primitive: Z"

 * This can iterate over values only:

   for (Map.Entry<String, List<String>> entry : dmhMethods.entrySet()) {
      count += entry.getValue().size();
   }

 * I don't know the module visibility rules between jlink and java.base,
but can we reference DirectMethodHandle.DMH class as literal from the
plugin?

 * requireBasicType(last) is loop invariant here:

    for (int j = 1; j < count; j++) {
        requireBasicType(last);
        sb.append(last);
    }

Thanks,
-Aleksey