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Memory provides high-performance native memory access.
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/*
 * Copyright 2018, Yahoo! Inc. Licensed under the terms of the
 * Apache License 2.0. See LICENSE file at the project root for terms.
 */

package com.yahoo.memory;

import static com.yahoo.memory.UnsafeUtil.unsafe;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.concurrent.atomic.AtomicLong;

/**
 * Provide linkage to java.nio.Bits.
 *
 * @author Lee Rhodes
 */
final class NioBits {
  private static final Class VM_CLASS;
  private static final Method VM_MAX_DIRECT_MEMORY_METHOD;
  private static final Method VM_IS_DIRECT_MEMORY_PAGE_ALIGNED_METHOD;

  private static final Class NIO_BITS_CLASS;
  private static final Method NIO_BITS_RESERVE_MEMORY_METHOD;
  private static final Method NIO_BITS_UNRESERVE_MEMORY_METHOD;

  private static final AtomicLong nioBitsCount;
  private static final AtomicLong nioBitsReservedMemory;
  private static final AtomicLong nioBitsTotalCapacity;

  private static int pageSize = unsafe.pageSize();
  private static final long maxDBBMemory;
  private static final boolean isPageAligned;

  static {
    try {
      //TODO-JDK9 VM_CLASS = Class.forName("jdk.internal.misc.VM");
      VM_CLASS = Class.forName("sun.misc.VM");
      VM_MAX_DIRECT_MEMORY_METHOD =
          VM_CLASS.getDeclaredMethod("maxDirectMemory");
      VM_MAX_DIRECT_MEMORY_METHOD.setAccessible(true);
      maxDBBMemory = (long)VM_MAX_DIRECT_MEMORY_METHOD
          .invoke(null); //static method

      VM_IS_DIRECT_MEMORY_PAGE_ALIGNED_METHOD =
          VM_CLASS.getDeclaredMethod("isDirectMemoryPageAligned");
      VM_IS_DIRECT_MEMORY_PAGE_ALIGNED_METHOD.setAccessible(true);
      isPageAligned = (boolean)VM_IS_DIRECT_MEMORY_PAGE_ALIGNED_METHOD
          .invoke(null); //static method

      NIO_BITS_CLASS = Class.forName("java.nio.Bits");

      NIO_BITS_RESERVE_MEMORY_METHOD = NIO_BITS_CLASS
          .getDeclaredMethod("reserveMemory", long.class, int.class);
      NIO_BITS_RESERVE_MEMORY_METHOD.setAccessible(true);

      NIO_BITS_UNRESERVE_MEMORY_METHOD = NIO_BITS_CLASS
          .getDeclaredMethod("unreserveMemory", long.class, int.class);
      NIO_BITS_UNRESERVE_MEMORY_METHOD.setAccessible(true);

      final Field countField = NIO_BITS_CLASS.getDeclaredField("count");
      countField.setAccessible(true);
      nioBitsCount = (AtomicLong) (countField.get(null));

      final Field reservedMemoryField = NIO_BITS_CLASS.getDeclaredField("reservedMemory");
      reservedMemoryField.setAccessible(true);
      nioBitsReservedMemory = (AtomicLong) (reservedMemoryField.get(null));

      final Field totalCapacityField = NIO_BITS_CLASS.getDeclaredField("totalCapacity");
      totalCapacityField.setAccessible(true);
      nioBitsTotalCapacity = (AtomicLong) (totalCapacityField.get(null));

    } catch (final Exception e) {
      throw new RuntimeException("Could not acquire java.nio.Bits class: " + e.getClass()
      + UnsafeUtil.tryIllegalAccessPermit);
    }
  }

  private NioBits() { }

  static long getDirectAllocationsCount() {
    try {
      final long count = nioBitsCount.get();
      return count;
    } catch (final Exception e) {
      throw new RuntimeException("Cannot read Bits.count " + e);
    }
  }

  static long getReservedMemory() {
    try {
      final long resMem = nioBitsReservedMemory.get();
      return resMem;
    } catch (final Exception e) {
      throw new RuntimeException("Cannot read Bits.reservedMemory " + e);
    }
  }

  static long getTotalCapacity() {
    try {
      final long resMem = nioBitsTotalCapacity.get();
      return resMem;
    } catch (final Exception e) {
      throw new RuntimeException("Cannot read Bits.totalCapacity " + e);
    }
  }

  static int pageSize() {
    return pageSize;
  }

  static int pageCount(final long bytes) {
    return (int)((bytes + pageSize()) - 1L) / pageSize();
  }

  static long getMaxDirectByteBufferMemory() {
    return maxDBBMemory;
  }

  static boolean isPageAligned() {
    return isPageAligned;
  }

  //RESERVE & UNRESERVE BITS MEMORY TRACKING COUNTERS
  // Comment from java.nio.Bits.java ~ line 705:
  // -XX:MaxDirectMemorySize limits the total capacity rather than the
  // actual memory usage, which will differ when buffers are page aligned.
  static void reserveMemory(final long allocationSize, final long capacity) {
    try {
      reserveUnreserve(allocationSize, capacity, NIO_BITS_RESERVE_MEMORY_METHOD);
    } catch (final Exception e) {
      throw new RuntimeException("Could not invoke java.nio.Bits.reserveMemory(...): "
          + "allocationSize = " + allocationSize + ", capacity = " + capacity, e);
    }
  }

  static void unreserveMemory(final long allocationSize, final long capacity) {
    try {
      reserveUnreserve(allocationSize, capacity, NIO_BITS_UNRESERVE_MEMORY_METHOD);
    } catch (final Exception e) {
      throw new RuntimeException("Could not invoke java.nio.Bits.unreserveMemory(...): "
          + "allocationSize = " + allocationSize + ", capacity = " + capacity, e);
    }
  }

  private static void reserveUnreserve(long allocationSize, long capacity, final Method method)
      throws Exception {
    Util.zeroCheck(capacity, "capacity");
    // 1GB is a pretty "safe" limit.
    final long chunkSizeLimit = 1L << 30;
    while (capacity > 0) {
      final long chunk = Math.min(capacity, chunkSizeLimit);
      if (capacity == chunk) {
        method.invoke(null, allocationSize, (int) capacity);
      } else {
        method.invoke(null, chunk, (int) chunk);
      }
      capacity -= chunk;
      allocationSize -= chunk;
    }
  }
}