/*
 * Copyright (c) 2019, 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.
 *
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package com.oracle.svm.core.code;

import com.oracle.svm.core.SubstrateUtil;
import com.oracle.svm.core.annotate.Uninterruptible;
import com.oracle.svm.core.jdk.UninterruptibleUtils;
import com.oracle.svm.core.thread.VMOperation;

Every CodeInfo object has a corresponding CodeInfoTether that is used for managing the lifecycle of the unmanaged memory that is used for the CodeInfo object. As long as the CodeInfoTether is reachable by the GC, the CodeInfo object and its data will stay alive as well. If the CodeInfoTether is unreachable, the GC can decide to free the unmanaged memory at any subsequent safepoint. 
 Note however that frames on the stack can be deoptimized at any safepoint check, regardless of the reachability of the code's corresponding CodeInfoTether object. Later lookups via the instruction pointer can fail, so only the explicitly kept alive CodeInfo must be used. This also applies to usages within VMOperations as a GC can also be triggered there. /**
 * Every {@link CodeInfo} object has a corresponding {@link CodeInfoTether} that is used for
 * managing the lifecycle of the unmanaged memory that is used for the {@link CodeInfo} object. As
 * long as the {@link CodeInfoTether} is reachable by the GC, the {@link CodeInfo} object and its
 * data will stay alive as well. If the {@link CodeInfoTether} is unreachable, the GC can decide to
 * free the unmanaged memory at any subsequent safepoint.
 * <p>
 * Note however that frames on the stack can be deoptimized at any safepoint check, regardless of
 * the reachability of the code's corresponding {@link CodeInfoTether} object. Later lookups via the
 * instruction pointer can fail, so only the explicitly kept alive {@link CodeInfo} must be used.
 * This also applies to usages within {@link VMOperation}s as a GC can also be triggered there.
 */
public class CodeInfoTether {
    private final UninterruptibleUtils.AtomicInteger count;

    public CodeInfoTether(boolean acquired) {
        this.count = (SubstrateUtil.HOSTED || CodeInfoAccess.haveAssertions()) ? new UninterruptibleUtils.AtomicInteger(acquired ? 1 : 0) : null;
    }

    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
    public int getCount() {
        return count.get();
    }

    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
    public int incrementCount() {
        return count.incrementAndGet();
    }

    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
    public int decrementCount() {
        return count.decrementAndGet();
    }
}