/*
 * Copyright 2016-2020 Chronicle Software
 *
 * https://chronicle.software
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.openhft.chronicle.core.io;

public abstract class SimpleCloseable implements Closeable, ReferenceOwner {
    private transient boolean closed;

    protected SimpleCloseable() {
    }

    /**
     * Close a resource so it cannot be used again.
     */
    @Override
    public final void close() {
        if (closed)
            return;
        performClose();
    }

    /**
     * Call close() to ensure this is called exactly once.
     */
    protected abstract void performClose();

    @Override
    public boolean isClosed() {
        return closed;
    }
}

/*
 * Copyright 2016-2020 Chronicle Software
 *
 * https://chronicle.software
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.openhft.chronicle.core.io;

public abstract class SimpleCloseable implements Closeable, ReferenceOwner {
    private transient boolean closed;

    protected SimpleCloseable() {
    }

    /**
     * Close a resource so it cannot be used again.
     */
    @Override
    public final void close() {
        if (closed)
            return;
        performClose();
    }

    /**
     * Call close() to ensure this is called exactly once.
     */
    protected void performClose() {
        // might be nothing.
    }

    @Override
    public boolean isClosed() {
        return closed;
    }
}

Make more resource trace whether they were closed properly or not, https://github.com/OpenHFT/Chronicle-Core/issues/116