--- /dev/null
+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <folly/detail/CachelinePaddedImpl.h>
+
+namespace folly {
+
+/**
+ * Holds a type T, in addition to enough padding to round the size up to the
+ * next multiple of the false sharing range used by folly.
+ *
+ * If T is standard-layout, then casting a T* you get from this class to a
+ * CachelinePadded<T>* is safe.
+ *
+ * This class handles padding, but imperfectly handles alignment. (Note that
+ * alignment matters for false-sharing: imagine a cacheline size of 64, and two
+ * adjacent 64-byte objects, with the first starting at an offset of 32. The
+ * last 32 bytes of the first object share a cacheline with the first 32 bytes
+ * of the second.). We alignas this class to be at least cacheline-sized, but
+ * it's implementation-defined what that means (since a cacheline is almost
+ * certainly larger than the maximum natural alignment). The following should be
+ * true for recent compilers on common architectures:
+ *
+ * For heap objects, alignment needs to be handled at the allocator level, such
+ * as with posix_memalign (this isn't necessary with jemalloc, which aligns
+ * objects that are a multiple of cacheline size to a cacheline).
+ *
+ * For static and stack objects, the alignment should be obeyed, and no specific
+ * intervention is necessary.
+ */
+template <typename T>
+class CachelinePadded {
+ public:
+ template <typename... Args>
+ explicit CachelinePadded(Args&&... args)
+ : impl_(std::forward<Args>(args)...) {}
+
+ CachelinePadded() {}
+
+ T* get() {
+ return &impl_.item;
+ }
+
+ const T* get() const {
+ return &impl_.item;
+ }
+
+ T* operator->() {
+ return get();
+ }
+
+ const T* operator->() const {
+ return get();
+ }
+
+ T& operator*() {
+ return *get();
+ }
+
+ const T& operator*() const {
+ return *get();
+ }
+
+ private:
+ detail::CachelinePaddedImpl<T> impl_;
+};
+}
--- /dev/null
+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <folly/detail/CacheLocality.h>
+
+namespace folly {
+
+template <typename T>
+class CachelinePadded;
+
+namespace detail {
+
+template <
+ typename T,
+ bool needsPadding = (sizeof(T) % CacheLocality::kFalseSharingRange != 0)>
+struct CachelinePaddedImpl;
+
+// We need alignas(T) alignas(kFalseSharingRange) for the case where alignof(T)
+// > alignof(kFalseSharingRange).
+template <typename T>
+struct alignas(T) alignas(detail::CacheLocality::kFalseSharingRange)
+ CachelinePaddedImpl<T, /* needsPadding = */ false> {
+ template <typename... Args>
+ explicit CachelinePaddedImpl(Args&&... args)
+ : item(std::forward<Args>(args)...) {}
+ T item;
+};
+
+template <typename T>
+struct alignas(T) alignas(detail::CacheLocality::kFalseSharingRange)
+ CachelinePaddedImpl<T, /* needsPadding = */ true> {
+ template <typename... Args>
+ explicit CachelinePaddedImpl(Args&&... args)
+ : item(std::forward<Args>(args)...) {}
+
+ T item;
+ char padding
+ [CacheLocality::kFalseSharingRange -
+ sizeof(T) % CacheLocality::kFalseSharingRange];
+};
+} // namespace detail
+} // namespace folly
--- /dev/null
+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * 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.
+ */
+
+#include <folly/CachelinePadded.h>
+
+#include <type_traits>
+
+#include <gtest/gtest.h>
+
+using folly::CachelinePadded;
+
+static_assert(
+ std::is_standard_layout<CachelinePadded<int>>::value,
+ "CachelinePadded<T> must be standard-layout if T is.");
+
+const int kCachelineSize = folly::detail::CacheLocality::kFalseSharingRange;
+
+template <int dataSize>
+struct SizedData {
+ SizedData() {
+ for (unsigned i = 0; i < dataSize; ++i) {
+ data[i] = i;
+ }
+ }
+
+ void doModifications() {
+ for (unsigned i = 0; i < dataSize; ++i) {
+ EXPECT_EQ(static_cast<unsigned char>(i), data[i]);
+ ++data[i];
+ }
+ }
+
+ ~SizedData() {
+ for (unsigned i = 0; i < dataSize; ++i) {
+ EXPECT_EQ(static_cast<unsigned char>(i + 1), data[i]);
+ }
+ }
+
+ unsigned char data[dataSize];
+};
+
+using ExactlyCachelineSized = SizedData<kCachelineSize>;
+using DoubleCachelineSized = SizedData<2 * kCachelineSize>;
+using BelowCachelineSized = SizedData<kCachelineSize / 2>;
+using AboveCachelineSized = SizedData<kCachelineSize + kCachelineSize / 2>;
+
+TEST(CachelinePadded, Exact) {
+ EXPECT_EQ(kCachelineSize, sizeof(CachelinePadded<ExactlyCachelineSized>));
+ CachelinePadded<ExactlyCachelineSized> item;
+ item.get()->doModifications();
+ EXPECT_TRUE(
+ reinterpret_cast<CachelinePadded<ExactlyCachelineSized>*>(item.get()) ==
+ &item);
+}
+
+TEST(CachelinePadded, Double) {
+ EXPECT_EQ(2 * kCachelineSize, sizeof(CachelinePadded<DoubleCachelineSized>));
+ CachelinePadded<DoubleCachelineSized> item;
+ item.get()->doModifications();
+ EXPECT_TRUE(
+ reinterpret_cast<CachelinePadded<DoubleCachelineSized>*>(item.get()) ==
+ &item);
+}
+
+TEST(CachelinePadded, Below) {
+ EXPECT_EQ(kCachelineSize, sizeof(CachelinePadded<BelowCachelineSized>));
+ CachelinePadded<BelowCachelineSized> item;
+ item.get()->doModifications();
+ EXPECT_TRUE(
+ reinterpret_cast<CachelinePadded<BelowCachelineSized>*>(item.get()) ==
+ &item);
+}
+
+TEST(CachelinePadded, Above) {
+ EXPECT_EQ(2 * kCachelineSize, sizeof(CachelinePadded<AboveCachelineSized>));
+ CachelinePadded<AboveCachelineSized> item;
+ item.get()->doModifications();
+ EXPECT_TRUE(
+ reinterpret_cast<CachelinePadded<AboveCachelineSized>*>(item.get()) ==
+ &item);
+}
+
+TEST(CachelinePadded, CanBeCastedBack) {
+ CachelinePadded<int> padded;
+ CachelinePadded<int>* ptr =
+ reinterpret_cast<CachelinePadded<int>*>(padded.get());
+ EXPECT_EQ(&padded, ptr);
+}
+
+TEST(CachelinePadded, PtrOperator) {
+ CachelinePadded<int> padded;
+ EXPECT_TRUE(padded.get() == padded.operator->());
+ EXPECT_TRUE(&*padded == padded.get());
+ const CachelinePadded<int> constPadded;
+ EXPECT_TRUE(constPadded.get() == constPadded.operator->());
+ EXPECT_TRUE(constPadded.get() == &*constPadded.get());
+}
+
+TEST(CachelinePadded, PropagatesConstness) {
+ struct OverloadedOnConst {
+ void assign(int* dst) {
+ *dst = 31415;
+ }
+ void assign(int* dst) const {
+ *dst = 271828;
+ }
+ };
+
+ CachelinePadded<OverloadedOnConst> padded;
+
+ int i = 0;
+ padded->assign(&i);
+ EXPECT_EQ(31415, i);
+
+ const CachelinePadded<OverloadedOnConst> constPadded;
+ constPadded->assign(&i);
+ EXPECT_EQ(271828, i);
+}
+
+TEST(CachelinePadded, ConstructsAndDestructs) {
+ enum LifetimeStatus {
+ kNone,
+ kConstructed,
+ kDestroyed,
+ };
+ struct WriteOnLifetimeOp {
+ explicit WriteOnLifetimeOp(LifetimeStatus* dst) : dst_(dst) {
+ *dst = kConstructed;
+ }
+ ~WriteOnLifetimeOp() {
+ *dst_ = kDestroyed;
+ }
+ LifetimeStatus* dst_;
+ };
+ LifetimeStatus status = kNone;
+ CachelinePadded<WriteOnLifetimeOp>* ptr =
+ new CachelinePadded<WriteOnLifetimeOp>(&status);
+ EXPECT_EQ(kConstructed, status);
+ delete ptr;
+ EXPECT_EQ(kDestroyed, status);
+}
+
+TEST(CachelinePadded, ConstructsAndDestructsArrays) {
+ static thread_local int numConstructions;
+ static thread_local int numDestructions;
+ numConstructions = 0;
+ numDestructions = 0;
+ struct LifetimeCountingClass {
+ LifetimeCountingClass() {
+ ++numConstructions;
+ }
+ ~LifetimeCountingClass() {
+ ++numDestructions;
+ }
+ };
+ const static int kNumItems = 123;
+ CachelinePadded<LifetimeCountingClass>* ptr =
+ new CachelinePadded<LifetimeCountingClass>[kNumItems];
+ EXPECT_EQ(kNumItems, numConstructions);
+ delete[] ptr;
+ EXPECT_EQ(kNumItems, numDestructions);
+}
+
+TEST(CachelinePadded, ForwardsCorrectly) {
+ struct RvalueOverloadedConstructor {
+ RvalueOverloadedConstructor(int* dst, int& /* ignored */) {
+ *dst = 0;
+ }
+ RvalueOverloadedConstructor(int* dst, int&& /* ignored */) {
+ *dst = 1;
+ }
+ };
+ int shouldBeZero = 12345;
+ int shouldBeOne = 67890;
+ {
+ int ignored = 42;
+ CachelinePadded<RvalueOverloadedConstructor> padded1(
+ &shouldBeZero, ignored);
+ CachelinePadded<RvalueOverloadedConstructor> padded2(
+ &shouldBeOne, static_cast<int&&>(ignored));
+ }
+ EXPECT_EQ(0, shouldBeZero);
+ EXPECT_EQ(1, shouldBeOne);
+}
projects / folly.git / commitdiff