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BTrace: A safe, dynamic tracing tool for the Java platform

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/*
 * Copyright (c) 2008, 2015, 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,
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 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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import org.openjdk.btrace.core.annotations.BTrace;
import org.openjdk.btrace.core.annotations.Export;
import org.openjdk.btrace.core.annotations.OnMethod;
import org.openjdk.btrace.core.annotations.OnTimer;
import org.openjdk.btrace.core.annotations.Self;

import static org.openjdk.btrace.core.BTraceUtils.Counters;
import static org.openjdk.btrace.core.BTraceUtils.println;

/**
 * This sample creates a jvmstat counter and
 * increments it everytime Thread.start() is
 * called. This thread count may be accessed
 * from outside the process. The @Export annotated
 * fields are mapped to jvmstat counters. The counter
 * name is "btrace." +  + "." + 
 */
@BTrace
public class ThreadCounter {

    // create a jvmstat counter using @Export
    @Export
    private static long count;

    @OnMethod(
            clazz = "java.lang.Thread",
            method = "start"
    )
    public static void onnewThread(@Self Thread t) {
        // updating counter is easy. Just assign to
        // the static field!
        count++;
    }

    @OnTimer(2000)
    public static void ontimer() {
        // we can access counter as "count" as well
        // as from jvmstat counter directly.
        println(count);
        // or equivalently ...
        println(Counters.perfLong("btrace.org.openjdk.btrace.samples.ThreadCounter.count"));
    }
}