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8257189: Handle concurrent updates of MH.form better

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Reviewed-by: redestad, psandoz
This commit is contained in:
Vladimir Ivanov 2020-12-02 17:35:41 +00:00
parent 670426646d
commit 692b273ec5
5 changed files with 69 additions and 53 deletions
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67
src/java.base/share/classes/java/lang/invoke/MethodHandle.java
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@ -30,13 +30,13 @@ import jdk.internal.vm.annotation.IntrinsicCandidate;
import java.lang.constant.ClassDesc;
import java.lang.constant.Constable;
import java.lang.constant.ConstantDesc;
import java.lang.constant.DirectMethodHandleDesc;
import java.lang.constant.MethodHandleDesc;
import java.lang.constant.MethodTypeDesc;
import java.util.Arrays;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Function;
import static java.lang.invoke.MethodHandleInfo.*;
import static java.lang.invoke.MethodHandleStatics.*;
@ -455,9 +455,8 @@ public abstract class MethodHandle implements Constable {
/*private*/
MethodHandle asTypeCache;
// asTypeCache is not private so that invokers can easily fetch it
/*non-public*/
byte customizationCount;
// customizationCount should be accessible from invokers
private byte customizationCount;
/**
* Reports the type of this method handle.
@ -1733,6 +1732,30 @@ assertEquals("[three, thee, tee]", asListFix.invoke((Object)argv).toString());
*/
abstract BoundMethodHandle rebind();
/* non-public */
void maybeCustomize() {
if (form.customized == null) {
byte count = customizationCount;
if (count >= CUSTOMIZE_THRESHOLD) {
customize();
} else {
customizationCount = (byte) (count + 1);
}
}
}
/** Craft a LambdaForm customized for this particular MethodHandle. */
/*non-public*/
void customize() {
updateForm(new Function<>() {
public LambdaForm apply(LambdaForm oldForm) {
return oldForm.customize(MethodHandle.this);
}
});
}
private volatile boolean updateInProgress; // = false;
/**
* Replace the old lambda form of this method handle with a new one.
* The new one must be functionally equivalent to the old one.
@ -1741,26 +1764,26 @@ assertEquals("[three, thee, tee]", asListFix.invoke((Object)argv).toString());
* Use with discretion.
*/
/*non-public*/
void updateForm(LambdaForm newForm) {
assert(newForm.customized == null || newForm.customized == this);
if (form == newForm) return;
newForm.prepare(); // as in MethodHandle.<init>
UNSAFE.putReference(this, FORM_OFFSET, newForm);
UNSAFE.fullFence();
}
/** Craft a LambdaForm customized for this particular MethodHandle */
/*non-public*/
void customize() {
final LambdaForm form = this.form;
if (form.customized == null) {
LambdaForm newForm = form.customize(this);
updateForm(newForm);
void updateForm(Function<LambdaForm, LambdaForm> updater) {
if (UNSAFE.compareAndSetBoolean(this, UPDATE_OFFSET, false, true)) { // updateInProgress = true
// Only 1 thread wins the race and updates MH.form field.
try {
LambdaForm oldForm = form;
LambdaForm newForm = updater.apply(oldForm);
if (oldForm != newForm) {
assert (newForm.customized == null || newForm.customized == this);
newForm.prepare(); // as in MethodHandle.<init>
UNSAFE.putReference(this, FORM_OFFSET, newForm);
UNSAFE.fullFence();
}
} finally {
updateInProgress = false;
}
} else {
assert(form.customized == this);
// Update got lost due to concurrent update. But callers don't care.
}
}
private static final long FORM_OFFSET
= UNSAFE.objectFieldOffset(MethodHandle.class, "form");
private static final long FORM_OFFSET = UNSAFE.objectFieldOffset(MethodHandle.class, "form");
private static final long UPDATE_OFFSET = UNSAFE.objectFieldOffset(MethodHandle.class, "updateInProgress");
}