ClosureNativePointer.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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).
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package com.oracle.truffle.nfi;

import java.util.HashMap;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Container object for the two pointers (data and code) that make up a closure on the native side.
 * The native closure is reference counted, with the reference count being stored in this object.
 *
 * By convention, the first reference is owned by the {@link LibFFIClosure} object and therefore
 * controlled by the Java GC. There should be no other references to this object from the Java side.
 * When the reference count drops to zero, the native side of this object is freed, so the Java side
 * contains garbage and must not be used anymore.
 */
final class ClosureNativePointer extends NativeAllocation.Destructor {

    private static final HashMap<Long, ClosureNativePointer> nativePointerMap = new HashMap<>();

    private static ClosureNativePointer get(long codePointer) {
        synchronized (nativePointerMap) {
            return nativePointerMap.get(codePointer);
        }
    }

    // called from native
    public static ClosureNativePointer create(long nativeClosure, long codePointer) {
        ClosureNativePointer ret = new ClosureNativePointer(nativeClosure, codePointer);
        synchronized (nativePointerMap) {
            nativePointerMap.put(codePointer, ret);
        }
        return ret;
    }

    // called from native
    public static void newClosureRef(long codePointer) {
        get(codePointer).addRef();
    }

    // called from native
    public static void releaseClosureRef(long codePointer) {
        get(codePointer).destroy();
    }

    private final long nativeClosure;
    private final long codePointer;

    private final AtomicInteger refCount;

    private ClosureNativePointer(long nativeClosure, long codePointer) {
        this.nativeClosure = nativeClosure;
        this.codePointer = codePointer;

        // the first reference is owned by the LibFFIClosure object
        this.refCount = new AtomicInteger(1);
    }

    void addRef() {
        int refs = refCount.getAndIncrement();
        assert refs > 0 : "addRef on dead closure";
    }

    @Override
    protected void destroy() {
        int refs = refCount.decrementAndGet();
        assert refs >= 0 : "destroy on already dead closure";
        if (refs == 0) {
            synchronized (nativePointerMap) {
                nativePointerMap.remove(codePointer);
            }
            freeClosure(nativeClosure);
        }
    }

    long getCodePointer() {
        assert refCount.get() > 0 : "accessing dead closure";
        return codePointer;
    }

    private static native void freeClosure(long closure);
}