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8341903: Implementation of Scoped Values (Fourth Preview)

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Reviewed-by: alanb
This commit is contained in:
Andrew Haley 2024-11-05 17:12:17 +00:00
parent 839de82c31
commit 3fab8e37bb
7 changed files with 88 additions and 157 deletions
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111
src/java.base/share/classes/java/lang/ScopedValue.java
View file

@ -75,34 +75,34 @@ import sun.security.action.GetPropertyAction;
* // @link substring="newInstance" target="#newInstance" :
* private static final ScopedValue<String> NAME = ScopedValue.newInstance();
*
* // @link substring="runWhere" target="#runWhere(ScopedValue, Object, Runnable)" :
* ScopedValue.runWhere(NAME, "duke", () -> doSomething());
* // @link substring="run" target="Carrier#run(Runnable)" :
* ScopedValue.where(NAME, "duke").run(() -> doSomething());
* }
* Code executed directly or indirectly by {@code doSomething}, with access to the field
* {@code NAME}, can invoke {@code NAME.get()} to read the value "{@code duke}". {@code
* NAME} is bound while executing the {@code run} method. It reverts to being unbound when
* the {@code run} method completes.
*
* <p> The example using {@code runWhere} invokes a method that does not return a result.
* The {@link #callWhere(ScopedValue, Object, CallableOp) callWhere} method can be used
* <p> The example using {@code run} invokes a method that does not return a result.
* The {@link Carrier#call(CallableOp) call} method can be used
* to invoke a method that returns a result.
* In addition, {@code ScopedValue} defines the {@link #where(ScopedValue, Object)} method
* {@code ScopedValue} defines the {@link #where(ScopedValue, Object)} method
* for cases where multiple mappings (of {@code ScopedValue} to value) are accumulated
* in advance of calling a method with all {@code ScopedValue}s bound to their value.
*
* <h2>Bindings are per-thread</h2>
*
* A {@code ScopedValue} binding to a value is per-thread. Invoking {@code xxxWhere}
* A {@code ScopedValue} binding to a value is per-thread. Invoking {@code run}
* executes a method with a {@code ScopedValue} bound to a value for the current thread.
* The {@link #get() get} method returns the value bound for the current thread.
*
* <p> In the example, if code executed by one thread invokes this:
* {@snippet lang=java :
* ScopedValue.runWhere(NAME, "duke1", () -> doSomething());
* ScopedValue.where(NAME, "duke1").run(() -> doSomething());
* }
* and code executed by another thread invokes:
* {@snippet lang=java :
* ScopedValue.runWhere(NAME, "duke2", () -> doSomething());
* ScopedValue.where(NAME, "duke2").run(() -> doSomething());
* }
* then code in {@code doSomething} (or any method that it calls) invoking {@code NAME.get()}
* will read the value "{@code duke1}" or "{@code duke2}", depending on which thread is
@ -129,7 +129,7 @@ import sun.security.action.GetPropertyAction;
* <p> In the above example, suppose that code executed by {@code doSomething} binds
* {@code NAME} to a new value with:
* {@snippet lang=java :
* ScopedValue.runWhere(NAME, "duchess", () -> doMore());
* ScopedValue.where(NAME, "duchess").run(() -> doMore());
* }
* Code executed directly or indirectly by {@code doMore()} that invokes {@code
* NAME.get()} will read the value "{@code duchess}". When {@code doMore()} completes
@ -157,14 +157,18 @@ import sun.security.action.GetPropertyAction;
* {@snippet lang=java :
* private static final ScopedValue<String> NAME = ScopedValue.newInstance();
* ScopedValue.runWhere(NAME, "duke", () -> {
* ScopedValue.where(NAME, "duke").run(() -> {
* try (var scope = new StructuredTaskScope<String>()) {
*
* scope.fork(() -> childTask1());
* scope.fork(() -> childTask2());
* scope.fork(() -> childTask3());
* // @link substring="fork" target="StructuredTaskScope#fork(java.util.concurrent.Callable)" :
* scope.fork(() -> childTask1());
* scope.fork(() -> childTask2());
* scope.fork(() -> childTask3());
*
* ...
* // @link substring="join" target="StructuredTaskScope#join()" :
* scope.join();
*
* ..
* }
* });
* }
@ -310,7 +314,7 @@ public final class ScopedValue<T> {
*/
@PreviewFeature(feature = PreviewFeature.Feature.SCOPED_VALUES)
public static final class Carrier {
// Bit masks: a 1 in postion n indicates that this set of bound values
// Bit masks: a 1 in position n indicates that this set of bound values
// hits that slot in the cache.
final int bitmask;
final ScopedValue<?> key;
@ -385,7 +389,7 @@ public final class ScopedValue<T> {
return (T) value;
}
}
throw new NoSuchElementException();
throw new NoSuchElementException("No mapping present");
}
/**
@ -409,7 +413,6 @@ public final class ScopedValue<T> {
* @return the result
* @throws StructureViolationException if a structure violation is detected
* @throws X if {@code op} completes with an exception
* @see ScopedValue#callWhere(ScopedValue, Object, CallableOp)
* @since 23
*/
public <R, X extends Throwable> R call(CallableOp<? extends R, X> op) throws X {
@ -458,7 +461,6 @@ public final class ScopedValue<T> {
*
* @param op the operation to run
* @throws StructureViolationException if a structure violation is detected
* @see ScopedValue#runWhere(ScopedValue, Object, Runnable)
*/
public void run(Runnable op) {
Objects.requireNonNull(op);
@ -528,77 +530,6 @@ public final class ScopedValue<T> {
return Carrier.of(key, value);
}
/**
* Calls a value-returning operation with a {@code ScopedValue} bound to a value
* in the current thread. When the operation completes (normally or with an
* exception), the {@code ScopedValue} will revert to being unbound, or revert to
* its previous value when previously bound, in the current thread. If {@code op}
* completes with an exception then it propagated by this method.
*
* <p> Scoped values are intended to be used in a <em>structured manner</em>. If code
* invoked directly or indirectly by the operation creates a {@link StructuredTaskScope}
* but does not {@linkplain StructuredTaskScope#close() close} it, then it is detected
* as a <em>structure violation</em> when the operation completes (normally or with an
* exception). In that case, the underlying construct of the {@code StructuredTaskScope}
* is closed and {@link StructureViolationException} is thrown.
*
* @implNote
* This method is implemented to be equivalent to:
* {@snippet lang=java :
* // @link substring="call" target="Carrier#call(CallableOp)" :
* ScopedValue.where(key, value).call(op);
* }
*
*
*
* @param key the {@code ScopedValue} key
* @param value the value, can be {@code null}
* @param <T> the type of the value
* @param <R> the result type
* @param <X> type of the exception thrown by the operation
* @param op the operation to call
* @return the result
* @throws StructureViolationException if a structure violation is detected
* @throws X if the operation completes with an exception
* @since 23
*/
public static <T, R, X extends Throwable> R callWhere(ScopedValue<T> key,
T value,
CallableOp<? extends R, X> op) throws X {
return where(key, value).call(op);
}
/**
* Run an operation with a {@code ScopedValue} bound to a value in the current
* thread. When the operation completes (normally or with an exception), the
* {@code ScopedValue} will revert to being unbound, or revert to its previous value
* when previously bound, in the current thread. If {@code op} completes with an
* exception then it propagated by this method.
*
* <p> Scoped values are intended to be used in a <em>structured manner</em>. If code
* invoked directly or indirectly by the operation creates a {@link StructuredTaskScope}
* but does not {@linkplain StructuredTaskScope#close() close} it, then it is detected
* as a <em>structure violation</em> when the operation completes (normally or with an
* exception). In that case, the underlying construct of the {@code StructuredTaskScope}
* is closed and {@link StructureViolationException} is thrown.
*
* @implNote
* This method is implemented to be equivalent to:
* {@snippet lang=java :
* // @link substring="run" target="Carrier#run(Runnable)" :
* ScopedValue.where(key, value).run(op);
* }
*
* @param key the {@code ScopedValue} key
* @param value the value, can be {@code null}
* @param <T> the type of the value
* @param op the operation to call
* @throws StructureViolationException if a structure violation is detected
*/
public static <T> void runWhere(ScopedValue<T> key, T value, Runnable op) {
where(key, value).run(op);
}
private ScopedValue() {
this.hash = generateKey();
}
@ -642,7 +573,7 @@ public final class ScopedValue<T> {
private T slowGet() {
var value = findBinding();
if (value == Snapshot.NIL) {
throw new NoSuchElementException();
throw new NoSuchElementException("ScopedValue not bound");
}
Cache.put(this, value);
return (T)value;

4
src/java.base/share/classes/java/util/concurrent/StructuredTaskScope.java
View file

@ -261,8 +261,8 @@ import jdk.internal.invoke.MhUtil;
* {@snippet lang=java :
* private static final ScopedValue<String> USERNAME = ScopedValue.newInstance();
*
* // @link substring="runWhere" target="ScopedValue#runWhere(ScopedValue, Object, Runnable)" :
* ScopedValue.runWhere(USERNAME, "duke", () -> {
* // @link substring="run" target="ScopedValue.Carrier#run(Runnable)" :
* ScopedValue.where(USERNAME, "duke").run(() -> {
* try (var scope = new StructuredTaskScope<String>()) {
*
* scope.fork(() -> childTask()); // @highlight substring="fork"

2
src/java.base/share/classes/javax/security/auth/Subject.java
View file

@ -436,7 +436,7 @@ public final class Subject implements java.io.Serializable {
Objects.requireNonNull(action);
if (!SharedSecrets.getJavaLangAccess().allowSecurityManager()) {
try {
return ScopedValue.callWhere(SCOPED_SUBJECT, subject, action::call);
return ScopedValue.where(SCOPED_SUBJECT, subject).call(action::call);
} catch (Exception e) {
throw new CompletionException(e);
}

2
src/java.base/share/classes/jdk/internal/javac/PreviewFeature.java
View file

@ -70,7 +70,7 @@ public @interface PreviewFeature {
//---
@JEP(number=477, title="Implicitly Declared Classes and Instance Main Methods", status="Third Preview")
IMPLICIT_CLASSES,
@JEP(number=481, title="Scoped Values", status="Third Preview")
@JEP(number=487, title="Scoped Values", status="Fourth Preview")
SCOPED_VALUES,
@JEP(number=480, title="Structured Concurrency", status="Third Preview")
STRUCTURED_CONCURRENCY,