JDK14/Java14源码在线阅读

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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,
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package jdk.jfr.internal;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import jdk.jfr.Enabled;
import jdk.jfr.RecordingState;
import jdk.jfr.internal.settings.CutoffSetting;
import jdk.jfr.internal.test.WhiteBox;

// The Old Object event could have been implemented as a periodic event, but
// due to chunk rotations and how settings are calculated when multiple recordings
// are running at the same time, it would lead to unacceptable overhead.
//
// Instead, the event is only emitted before a recording stops and
// if that recording has the event enabled.
//
// This requires special handling and the purpose of this class is to provide that
//
public final class OldObjectSample {

    private static final String EVENT_NAME = Type.EVENT_NAME_PREFIX + "OldObjectSample";
    private static final String OLD_OBJECT_CUTOFF = EVENT_NAME + "#" + Cutoff.NAME;
    private static final String OLD_OBJECT_ENABLED = EVENT_NAME + "#" + Enabled.NAME;

    // Emit if old object is enabled in recording with cutoff for that recording
    public static void emit(PlatformRecording recording) {
        if (isEnabled(recording)) {
            long nanos = CutoffSetting.parseValueSafe(recording.getSettings().get(OLD_OBJECT_CUTOFF));
            long ticks = Utils.nanosToTicks(nanos);
            JVM.getJVM().emitOldObjectSamples(ticks, WhiteBox.getWriteAllObjectSamples());
        }
    }

    // Emit if old object is enabled for at least one recording, and use the largest
    // cutoff for an enabled recording
    public static void emit(List<PlatformRecording> recordings, Boolean pathToGcRoots) {
        boolean enabled = false;
        long cutoffNanos = Boolean.TRUE.equals(pathToGcRoots) ? Long.MAX_VALUE : 0L;
        for (PlatformRecording r : recordings) {
            if (r.getState() == RecordingState.RUNNING) {
                if (isEnabled(r)) {
                    enabled = true;
                    long c = CutoffSetting.parseValueSafe(r.getSettings().get(OLD_OBJECT_CUTOFF));
                    cutoffNanos = Math.max(c, cutoffNanos);
                }
            }
        }
        if (enabled) {
            long ticks = Utils.nanosToTicks(cutoffNanos);
            JVM.getJVM().emitOldObjectSamples(ticks, WhiteBox.getWriteAllObjectSamples());
        }
    }

    public static void updateSettingPathToGcRoots(Map<String, String> s, Boolean pathToGcRoots) {
        if (pathToGcRoots != null) {
            s.put(OLD_OBJECT_CUTOFF, pathToGcRoots ? "infinity" : "0 ns");
        }
    }


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