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/*
* Copyright (c) 2021 Contributors to the Eclipse Foundation
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0, which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the
* Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
* version 2 with the GNU Classpath Exception, which is available at
* https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
*/
package jakarta.enterprise.concurrent.spi;
/**
* An immutable snapshot of a particular type of thread context.
*
* The captured context represented by this snapshot can be applied to
* any number of threads, including concurrently.
*
* Any state that is associated with context applied to a thread should
* be kept, not within the snapshot, but within the distinct
* {@link ThreadContextRestorer} instance that this
* {@code ThreadContextSnapshot} creates each time it is applied
* to a thread.
*
* @since 3.0
*/
@FunctionalInterface
public interface ThreadContextSnapshot {
/**
* Applies the captured thread context snapshot to the current thread and
* returns a distinct {@link ThreadContextRestorer} instance. The
* {@code ThreadContextRestorer} instance tracks the context's life cycle,
* including any state that is associated with it or that is necessary for
* restoring the previous context.
*
* For each invocation of this method, the Jakarta EE Product Provider
* must invoke the corresponding
* {@link ThreadContextRestorer#endContext endContext}
* method exactly once, such that the previous context is restored
* on the thread. If the Jakarta EE Product Provider sequentially begins
* multiple {@code ThreadContextRestorer} instances on a thread,
* it must invoke the corresponding {@code endContext} methods in reverse
* order.
*
* @return restorer instance that reverts the state of this context type
* on the thread to what it was prior to applying this snapshot.
*/
public ThreadContextRestorer begin();
}