Here's a bit of new about invokedynamic: I just pushed my updated
code (about 10KLOC) to an OpenJDK integration area:
http://hg.openjdk.java.net/jdk7/tl/jdk/file/tip/src/share/classes/java/dyn/
It's much more functional than before. See demo below for a small
example. Or look at the combinator definitions (e.g., FromGeneric) in
the JDK code.
I'm 2/3 done pulling that version back into mlvm patches, on top of
bsd-port.
Over time, the official JDK bits get integrated first into Sun's
weekly builds, and then they (I hope) will flow to the BSD-port repo,
allowing the MLVM patch set to shrink. This may make private
"bleeding edge" builds easier to cope with.
Best wishes,
-- John
import java.dyn.*;
import static java.dyn.MethodHandles.*;
import static java.dyn.MethodType.*;
public class FidgetDemo {
public static void main(String... av) {
if (av.length == 0) av = new String[]{ "fred", "buster",
"ricky" };
System.out.println("Fidgety self-modifying call site...");
for (int i = 0; i < 6; i++) {
System.out.println("--- loop #"+i);
for (String a : av) {
String result = InvokeDynamic.<String>fidget(a);
System.out.println(result);
}
}
}
private static String itch(String x) { return x+" can't get
comfortable"; }
private static String fuss(String x) { return x+" is feeling
moody"; }
private static String bore(String x) { return x+" needs a change
of scenery"; }
private static final String[] NAMES = { "itch", "fuss", "bore" };
private static MethodHandle which(int i) {
return lookup().findStatic(FidgetDemo.class, NAMES[i %
NAMES.length],
make(String.class, String.class));
}
// It is easy to build hybrid closure-like method handles out of
classes.
private static class Guard extends JavaMethodHandle {
MethodHandle target; // wrapped target
CSite site; // included site
// constructor folds a sneaky site reference into a direct
target
Guard(CSite site, MethodHandle target) {
super(INVOKE);
this.target = target;
this.site = site;
}
String invoke(String x) {
if ((++site.count & 3) == 0)
site.setTarget(new Guard(site, which(site.count)));
return target.<String>invoke(x);
}
private static final MethodHandle INVOKE =
lookup().findVirtual(Guard.class, "invoke",
make(String.class, String.class));
public String toString() { return "Guard:"+target.toString(); }
}
// Use a local call site subclass. (These are optional but fun.)
private static class CSite extends CallSite {
int count;
public CSite(Class caller, String name, MethodType type) {
super(caller, name, type);
//?? super(String.class, "gloat", make(void.class));
System.out.println("[link] new call site: "+this);
setTarget(new Guard(this, which(0)));
}
// this is just for the noise value:
public void setTarget(MethodHandle t) {
System.out.println("[link] set target to "+t);
super.setTarget(t);
}
}
// Set up a class-local bootstrap method.
static { Linkage.registerBootstrapMethod("linkDynamic"); }
private static CallSite linkDynamic(Class caller, String name,
MethodType type) {
assert((Object)name == "fidget" &&
type == make(String.class, String.class));
return new CSite(caller, name, type);
}
}
/* resulting output
--------
Fidgety self-modifying call site...
--- loop #0
[link] new call site:
CallSite#14491894[fidget(java.lang.String)java.lang.String => null]
[link] set target to Guard:itch(java.lang.String)java.lang.String
fred can't get comfortable
buster can't get comfortable
ricky can't get comfortable
--- loop #1
[link] set target to Guard:fuss(java.lang.String)java.lang.String
fred can't get comfortable
buster is feeling moody
ricky is feeling moody
--- loop #2
fred is feeling moody
[link] set target to Guard:bore(java.lang.String)java.lang.String
buster is feeling moody
ricky needs a change of scenery
--- loop #3
fred needs a change of scenery
buster needs a change of scenery
[link] set target to Guard:itch(java.lang.String)java.lang.String
ricky needs a change of scenery
--- loop #4
fred can't get comfortable
buster can't get comfortable
ricky can't get comfortable
--- loop #5
[link] set target to Guard:fuss(java.lang.String)java.lang.String
fred can't get comfortable
buster is feeling moody
ricky is feeling moody
--------
*/
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