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Java example source code file (Reentrancy.c)

This example Java source code file (Reentrancy.c) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

jni_false, jni_true, jplis_currently_inside_token, jplis_currently_outside_token, jplisassert_enableassertions, jvmti_error_none, null

The Reentrancy.c Java example source code

/*
 * Copyright (c) 2003, 2008, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * Copyright 2003 Wily Technology, Inc.
 */

#include    <jni.h>
#include    <jvmti.h>

#include    "JPLISAssert.h"
#include    "Reentrancy.h"
#include    "JPLISAgent.h"

/*
 *  This module provides some utility functions to support the "same thread" re-entrancy management.
 *  Uses JVMTI TLS to store a single bit per thread.
 *  Non-zero means the thread is already inside; zero means the thread is not inside.
 */

/*
 *  Local prototypes
 */

/* Wrapper around set that does the set then re-fetches to make sure it worked.
 * Degenerates to a simple set when assertions are disabled.
 * This routine is only here because of a bug in the JVMTI where set to 0 fails.
 */
jvmtiError
confirmingTLSSet(   jvmtiEnv *      jvmtienv,
                    jthread         thread,
                    const void *    newValue);

/* Confirmation routine only; used to assure that the TLS slot holds the value we expect it to. */
void
assertTLSValue( jvmtiEnv *      jvmtienv,
                jthread         thread,
                const void *    expected);


#define JPLIS_CURRENTLY_INSIDE_TOKEN                ((void *) 0x7EFFC0BB)
#define JPLIS_CURRENTLY_OUTSIDE_TOKEN               ((void *) 0)


jvmtiError
confirmingTLSSet(   jvmtiEnv *      jvmtienv,
                    jthread         thread,
                    const void *    newValue) {
    jvmtiError  error;

    error = (*jvmtienv)->SetThreadLocalStorage(
                                    jvmtienv,
                                    thread,
                                    newValue);
    check_phase_ret_blob(error, error);

#if JPLISASSERT_ENABLEASSERTIONS
    assertTLSValue( jvmtienv,
                    thread,
                    newValue);
#endif

    return error;
}

void
assertTLSValue( jvmtiEnv *      jvmtienv,
                jthread         thread,
                const void *    expected) {
    jvmtiError  error;
    void *      test = (void *) 0x99999999;

    /* now check if we do a fetch we get what we wrote */
    error = (*jvmtienv)->GetThreadLocalStorage(
                                jvmtienv,
                                thread,
                                &test);
    check_phase_ret(error);
    jplis_assert(error == JVMTI_ERROR_NONE);
    jplis_assert(test == expected);
}

jboolean
tryToAcquireReentrancyToken(    jvmtiEnv *  jvmtienv,
                                jthread     thread) {
    jboolean    result      = JNI_FALSE;
    jvmtiError  error       = JVMTI_ERROR_NONE;
    void *      storedValue = NULL;

    error = (*jvmtienv)->GetThreadLocalStorage(
                                jvmtienv,
                                thread,
                                &storedValue);
    check_phase_ret_false(error);
    jplis_assert(error == JVMTI_ERROR_NONE);
    if ( error == JVMTI_ERROR_NONE ) {
        /* if this thread is already inside, just return false and short-circuit */
        if ( storedValue == JPLIS_CURRENTLY_INSIDE_TOKEN ) {
            result = JNI_FALSE;
        }
        else {
            /* stuff in the sentinel and return true */
#if JPLISASSERT_ENABLEASSERTIONS
            assertTLSValue( jvmtienv,
                            thread,
                            JPLIS_CURRENTLY_OUTSIDE_TOKEN);
#endif
            error = confirmingTLSSet (  jvmtienv,
                                        thread,
                                        JPLIS_CURRENTLY_INSIDE_TOKEN);
            jplis_assert(error == JVMTI_ERROR_NONE);
            if ( error != JVMTI_ERROR_NONE ) {
                result = JNI_FALSE;
            }
            else {
                result = JNI_TRUE;
            }
        }
    }
    return result;
}


void
releaseReentrancyToken(         jvmtiEnv *  jvmtienv,
                                jthread     thread)  {
    jvmtiError  error       = JVMTI_ERROR_NONE;

/* assert we hold the token */
#if JPLISASSERT_ENABLEASSERTIONS
    assertTLSValue( jvmtienv,
                    thread,
                    JPLIS_CURRENTLY_INSIDE_TOKEN);
#endif

    error = confirmingTLSSet(   jvmtienv,
                                thread,
                                JPLIS_CURRENTLY_OUTSIDE_TOKEN);
    jplis_assert(error == JVMTI_ERROR_NONE);

}

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