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/OpenJDK 25

Interface StructuredTaskScope.Subtask<T>

Type Parameters:
T - the result type
All Superinterfaces:
Supplier<T>
Enclosing interface:
StructuredTaskScopePREVIEW<T,R>
public static sealed interface StructuredTaskScope.Subtask<T> extends Supplier<T>
Subtask is a preview API of the Java platform.
Programs can only use Subtask when preview features are enabled.
Preview features may be removed in a future release, or upgraded to permanent features of the Java platform.
Represents a subtask forked with StructuredTaskScope.fork(Callable)PREVIEW or StructuredTaskScope.fork(Runnable)PREVIEW.

Code that forks subtasks can use the get() method after joiningPREVIEW to obtain the result of a subtask that completed successfully. It can use the exception() method to obtain the exception thrown by a subtask that failed.

Since:
21

Nested Class Summary

Modifier and Type Interface Description
static enum  StructuredTaskScope.Subtask.StatePREVIEW
Preview.
Represents the state of a subtask.

Method Summary

Modifier and Type Method Description
Throwable exception()
Returns the exception or error thrown by this subtask if it failed.
T get()
Returns the result of this subtask if it completed successfully.
StructuredTaskScope.Subtask.StatePREVIEW state()
Returns the subtask state.

Method Details

state

StructuredTaskScope.Subtask.StatePREVIEW state()
Returns the subtask state.
Returns:
the subtask state

get

T get()
Returns the result of this subtask if it completed successfully. If the subtask was forked with fork(Callable)PREVIEW then the result from the call method is returned. If the subtask was forked with fork(Runnable)PREVIEW then null is returned.

Code executing in the scope owner thread can use this method to get the result of a successful subtask only after it has joinedPREVIEW.

Code executing in the Joiner onCompletePREVIEW method should test that the subtask state is SUCCESSPREVIEW before using this method to get the result.

Specified by:
get in interface Supplier<T>
Returns:
the possibly-null result
Throws:
IllegalStateException - if the subtask has not completed, did not complete successfully, or the current thread is the scope owner invoking this method before joiningPREVIEW
See Also:

exception

Throwable exception()
Returns the exception or error thrown by this subtask if it failed. If the subtask was forked with fork(Callable)PREVIEW then the exception or error thrown by the call method is returned. If the subtask was forked with fork(Runnable)PREVIEW then the exception or error thrown by the run method is returned.

Code executing in the scope owner thread can use this method to get the exception thrown by a failed subtask only after it has joinedPREVIEW.

Code executing in a Joiner onCompletePREVIEW method should test that the subtask state is FAILEDPREVIEW before using this method to get the exception.

Returns:
the exception or error thrown by this subtask if it failed
Throws:
IllegalStateException - if the subtask has not completed, completed with a result, or the current thread is the scope owner invoking this method before joiningPREVIEW
See Also:

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/concurrent/StructuredTaskScope.Subtask.html