| // Copyright 2023 The Bazel Authors. All rights reserved. |
| // |
| // 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 com.google.devtools.build.lib.concurrent; |
| |
| import static com.google.devtools.build.lib.unsafe.UnsafeProvider.unsafe; |
| |
| import com.google.common.annotations.VisibleForTesting; |
| import sun.misc.Unsafe; |
| |
| /** This class encapsulates creating padded addresses for 8-byte values. */ |
| final class PaddedAddresses { |
| /** |
| * The target alignment bytes. |
| * |
| * <p>On x86, the cache line size is 64-bytes, but spatial prefetching may fetch two lines at a |
| * time so interference is observable over a range of 128-bytes. |
| */ |
| @VisibleForTesting static final long ALIGNMENT = 128; |
| |
| /** The amount of padding needed between 8-byte objects to avoid interference. */ |
| private static final long PADDING_WIDTH = ALIGNMENT - 8; |
| |
| private PaddedAddresses() {} |
| |
| /** |
| * Creates a base address for the specified number of entries. |
| * |
| * <p>The caller must call {@link Unsafe#freeMemory} on the returned address. Use of {@link |
| * AddressFreer} could be helpful. |
| * |
| * @param count allocates a buffer large enough to accommodate this many aligned blocks. |
| */ |
| static long createPaddedBaseAddress(int count) { |
| return unsafe().allocateMemory(count * ALIGNMENT + PADDING_WIDTH); |
| } |
| |
| /** |
| * Obtains an {@link #ALIGNMENT} aligned address from an 8-byte aligned base address and offset. |
| * |
| * @param baseAddress an address obtained from {@link #createPaddedBaseAddress}. |
| * @param offset an offset less than the {@code count} parameter provided when creating the |
| * address. |
| */ |
| static long getAlignedAddress(long baseAddress, int offset) { |
| long cacheLineAddress = (baseAddress + PADDING_WIDTH) & ~(ALIGNMENT - 1); |
| return cacheLineAddress + offset * ALIGNMENT; |
| } |
| } |