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 * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package jdk.jfr.consumer;

import java.io.IOException;

import java.nio.file.Path;

import java.security.AccessControlContext;

import java.security.AccessController;

import java.time.Duration;

import java.time.Instant;

import java.util.Objects;

import java.util.function.Consumer;

import jdk.jfr.internal.SecuritySupport;

import jdk.jfr.internal.Utils;

import jdk.jfr.internal.consumer.EventDirectoryStream;

import jdk.jfr.internal.consumer.EventFileStream;

import jdk.jfr.internal.consumer.FileAccess;

/**

 * Represents a stream of events.

 * <p>

 * A stream is a sequence of events and the way to interact with a stream is to

 * register actions. The {@code EventStream} interface is not to be implemented

 * and future versions of the JDK may prevent this completely.

 * <p>

 * To receive a notification when an event arrives, register an action using the

 * {@link #onEvent(Consumer)} method. To filter the stream for an event with a

 * specific name, use {@link #onEvent(String, Consumer)} method.

 * <p>

 * By default, the same {@code RecordedEvent} object can be used for

 * representing two or more distinct events. The object can be delivered

 * multiple times to the same action as well as to other actions. If the life

 * span of the event object exceeds that of the action, the

 * {@link #setReuse(boolean)} method should be set to {@code false} so that a

 * new object is allocated for each event.

 * <p>

 * Events are delivered in batches. To receive a notification when a batch is

 * complete, register an action using the {@link #onFlush(Runnable)} method.

 * This is an opportunity to aggregate or push data to external systems while

 * the Java Virtual Machine (JVM) is preparing the next batch.

 * <p>

 * <p>

 * To dispatch events to registered actions, the stream must be started. To

 * start processing in the current thread, invoke the {@link #start()} method.

 * To process actions asynchronously in a separate thread, invoke the

 * {@link #startAsync()} method. To await completion of the stream, use the

 * awaitTermination {@link #awaitTermination()} or the {link

 * {@link #awaitTermination(Duration)} method.

 * <p>

 * When a stream ends it is automatically closed. To manually stop processing of

 * events, close the stream by invoking the {@link #close()} method. A stream

 * can also be automatically closed in exceptional circumstances, for example if

 * the JVM that is being monitored exits. To receive a notification in any of

 * these occasions, use the {@link #onClose(Runnable)} method to register an

 * action.

 * <p>

 * If an unexpected exception occurs in an action, it is possible to catch the

 * exception in an error handler. An error handler can be registered using the

 * {@link #onError(Runnable)} method. If no error handler is registered, the

 * default behavior is to print the exception and its backtrace to the standard

 * error stream.

 * <p>

 * The following example shows how an {@code EventStream} can be used to listen

 * to events on a JVM running Flight Recorder

 *

 * <pre>

 * <code>

 * try (EventStream es = EventStream.openRepository()) {

 *   es.onEvent("jdk.CPULoad", event -> {

 *     System.out.println("CPU Load " + event.getEndTime());

 *     System.out.println(" Machine total: " + 100 * event.getFloat("machineTotal") + "%");

 *     System.out.println(" JVM User: " + 100 * event.getFloat("jvmUser") + "%");

 *     System.out.println(" JVM System: " + 100 * event.getFloat("jvmSystem") + "%");

 *     System.out.println();

 *     System.gc();

 *   });

 *   es.onEvent("jdk.GarbageCollection", event -> {

 *     System.out.println("Garbage collection: " + event.getLong("gcId"));

 *     System.out.println(" Cause: " + event.getString("cause"));

 *     System.out.println(" Total pause: " + event.getDuration("sumOfPauses"));

 *     System.out.println(" Longest pause: " + event.getDuration("longestPause"));

 *     System.out.println();

 *   });

 *   es.start();

 * }

 * </code>

 * </pre>

 * <p>

 * To start recording together with the stream, see {@link RecordingStream}.

 *

 * @since 14

 */

public interface EventStream extends AutoCloseable {

    /**

     * Creates a stream from the repository of the current Java Virtual Machine

     * (JVM).

     * <p>

     * By default, the stream starts with the next event flushed by Flight

     * Recorder.

     *

     * @return an event stream, not {@code null}

     *

     * @throws IOException if a stream can't be opened, or an I/O error occurs

     *         when trying to access the repository

     *

     * @throws SecurityException if a security manager exists and the caller

     *         does not have

     *         {@code FlightRecorderPermission("accessFlightRecorder")}

     */

    public static EventStream openRepository() throws IOException {

        Utils.checkAccessFlightRecorder();

        return new EventDirectoryStream(AccessController.getContext(), null, SecuritySupport.PRIVILIGED, false);

    }

    /**

     * Creates an event stream from a disk repository.

     * <p>

     * By default, the stream starts with the next event flushed by Flight

     * Recorder.

     *

     * @param directory location of the disk repository, not {@code null}

     *

     * @return an event stream, not {@code null}

     *

     * @throws IOException if a stream can't be opened, or an I/O error occurs

     *         when trying to access the repository

     *

     * @throws SecurityException if a security manager exists and its

     *         {@code checkRead} method denies read access to the directory, or

     *         files in the directory.

     */

    public static EventStream openRepository(Path directory) throws IOException {

        Objects.nonNull(directory);

        AccessControlContext acc = AccessController.getContext();

        return new EventDirectoryStream(acc, directory, FileAccess.UNPRIVILIGED, false);

    }

    /**

     * Creates an event stream from a file.

     * <p>

     * By default, the stream starts with the first event in the file.

     *

     * @param file location of the file, not {@code null}

     *

     * @return an event stream, not {@code null}

     *

     * @throws IOException if the file can't be opened, or an I/O error occurs

     *         during reading

     *

     * @throws SecurityException if a security manager exists and its

     *         {@code checkRead} method denies read access to the file

     */

    static EventStream openFile(Path file) throws IOException {

        return new EventFileStream(AccessController.getContext(), file);

    }

    /**

     * Registers an action to perform on all events in the stream.

     *

     * @param action an action to perform on each {@code RecordedEvent}, not

     *        {@code null}

     */

    void onEvent(Consumer<RecordedEvent> action);

    /**

     * Registers an action to perform on all events matching a name.

     *

     * @param eventName the name of the event, not {@code null}

     *

     * @param action an action to perform on each {@code RecordedEvent} matching

     *        the event name, not {@code null}

     */

    void onEvent(String eventName, Consumer<RecordedEvent> action);

    /**

     * Registers an action to perform after the stream has been flushed.

     *

     * @param action an action to perform after the stream has been

     *        flushed, not {@code null}

     */

    void onFlush(Runnable action);

    /**

     * Registers an action to perform if an exception occurs.

     * <p>

     * if an action is not registered, an exception stack trace is printed to

     * standard error.

     * <p>

     * Registering an action overrides the default behavior. If multiple actions

     * have been registered, they are performed in the order of registration.

     * <p>

     * If this method itself throws an exception, resulting behavior is

     * undefined.

     *

     * @param action an action to perform if an exception occurs, not

     *        {@code null}

     */

    void onError(Consumer<Throwable> action);

    /**

     * Registers an action to perform when the stream is closed.

     * <p>

     * If the stream is already closed, the action will be performed immediately

     * in the current thread.

     *

     * @param action an action to perform after the stream is closed, not

     *        {@code null}

     * @see #close()

     */

    void onClose(Runnable action);

    /**

     * Releases all resources associated with this stream.

     */

    void close();

    /**

     * Unregisters an action.

     * <p>

     * If the action has been registered multiple times, all instances are

     * unregistered.

     *

     * @param action the action to unregister, not {@code null}

     *

     * @return {@code true} if the action was unregistered, {@code false}

     *         otherwise

     *

     * @see #onEvent(Consumer)

     * @see #onEvent(String, Consumer)

     * @see #onFlush(Runnable)

     * @see #onClose(Runnable)

     * @see #onError(Consumer)

     */

    boolean remove(Object action);

    /**

     * Specifies that the event object in an {@link #onEvent(Consumer)} action

     * can be reused.

     * <p>

     * If reuse is set to {@code true), an action should not keep a reference

     * to the event object after the action has completed.

     *

     * @param reuse {@code true} if an event object can be reused, {@code false}

     * otherwise

     */

    void setReuse(boolean reuse);

    /**

     * Specifies that events arrives in chronological order, sorted by the time

     * they were committed to the stream.

     *

     * @param ordered if event objects arrive in chronological order to

     *        {@code #onEvent(Consumer)}

     */

    void setOrdered(boolean ordered);

    /**

     * Specifies the start time of the stream.

     * <p>

     * The start time must be set before starting the stream

     *

     * @param startTime the start time, not {@code null}

     *

     * @throws IllegalStateException if the stream is already started

     *

     * @see #start()

     * @see #startAsync()

     */

    void setStartTime(Instant startTime);

    /**

     * Specifies the end time of the stream.

     * <p>

     * The end time must be set before starting the stream.

     * <p>

     * At end time, the stream is closed.

     *

     * @param endTime the end time, not {@code null}

     *

     * @throws IllegalStateException if the stream is already started

     *

     * @see #start()

     * @see #startAsync()

     */

    void setEndTime(Instant endTime);

    /**

     * Start processing of actions.

     * <p>

     * Actions are performed in the current thread.

     *

     * @throws IllegalStateException if the stream is already started or closed

     */

    void start();

    /**

     * Start asynchronous processing of actions.

     * <p>

     * Actions are performed in a single separate thread.

     *

     * @throws IllegalStateException if the stream is already started or closed

     */

    void startAsync();

    /**

     * Blocks until all actions are completed, or the stream is closed, or the

     * timeout occurs, or the current thread is interrupted, whichever happens

     * first.

     *

     * @param timeout the maximum time to wait, not {@code null}

     *

     * @throws IllegalArgumentException if timeout is negative

     * @throws InterruptedException if interrupted while waiting

     *

     * @see #start()

     * @see #startAsync()

     * @see Thread#interrupt()

     */

    void awaitTermination(Duration timeout) throws InterruptedException;

    /**

     * Blocks until all actions are completed, or the stream is closed, or the

     * current thread is interrupted, whichever happens first.

     *

     * @throws InterruptedException if interrupted while waiting

     *

     * @see #start()

     * @see #startAsync()

     * @see Thread#interrupt()

     */

    void awaitTermination() throws InterruptedException;

}