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Code responsible for parsing the Neo4j configuration.
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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.configuration.pagecache;

import static org.neo4j.configuration.GraphDatabaseSettings.pagecache_flush_buffer_size_in_pages;
import static org.neo4j.internal.unsafe.UnsafeUtil.allocateMemory;
import static org.neo4j.internal.unsafe.UnsafeUtil.free;
import static org.neo4j.io.pagecache.PageCache.PAGE_SIZE;

import org.neo4j.configuration.Config;
import org.neo4j.configuration.GraphDatabaseInternalSettings;
import org.neo4j.io.pagecache.buffer.NativeIOBuffer;
import org.neo4j.memory.MemoryTracker;

public class ConfigurableIOBuffer implements NativeIOBuffer {
    private static final long NOT_INITIALIZED = 0;
    private final boolean enabled;
    private final MemoryTracker memoryTracker;
    private final long bufferSize;
    private final long bufferAddress;
    private final long alignedAddress;
    private final long allocatedBytes;
    private boolean closed;

    public ConfigurableIOBuffer(Config config, MemoryTracker memoryTracker) {
        this.memoryTracker = memoryTracker;
        this.bufferSize = PAGE_SIZE * config.get(pagecache_flush_buffer_size_in_pages);
        this.allocatedBytes = bufferSize + PAGE_SIZE;
        boolean ioBufferEnabled = true;
        long address = NOT_INITIALIZED;
        try {
            address = allocateMemory(allocatedBytes, memoryTracker);
        } catch (Throwable t) {
            if (config.get(GraphDatabaseInternalSettings.print_page_buffer_allocation_trace)) {
                t.printStackTrace();
            }
            ioBufferEnabled = false;
        }
        this.bufferAddress = address;
        this.alignedAddress = address + PAGE_SIZE - (address % PAGE_SIZE);
        this.enabled = ioBufferEnabled;
    }

    @Override
    public boolean isEnabled() {
        return enabled;
    }

    @Override
    public boolean hasMoreCapacity(int used, int requestSize) {
        if (!enabled) {
            return false;
        }
        return used + requestSize <= bufferSize;
    }

    @Override
    public long getAddress() {
        return alignedAddress;
    }

    @Override
    public void close() {
        if (enabled && !closed) {
            free(bufferAddress, allocatedBytes, memoryTracker);
            closed = true;
        }
    }
}