diff options
Diffstat (limited to 'absl/strings')
| -rw-r--r-- | absl/strings/BUILD.bazel | 18 | ||||
| -rw-r--r-- | absl/strings/CMakeLists.txt | 2 | ||||
| -rw-r--r-- | absl/strings/cord.cc | 68 | ||||
| -rw-r--r-- | absl/strings/cord.h | 79 | ||||
| -rw-r--r-- | absl/strings/cord_buffer.cc | 28 | ||||
| -rw-r--r-- | absl/strings/cord_buffer.h | 571 | ||||
| -rw-r--r-- | absl/strings/cord_buffer_test.cc | 320 | ||||
| -rw-r--r-- | absl/strings/cord_test.cc | 278 |
8 files changed, 1364 insertions, 0 deletions
diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel index e9092165..81f5a589 100644 --- a/absl/strings/BUILD.bazel +++ b/absl/strings/BUILD.bazel @@ -415,9 +415,11 @@ cc_library( "cord.cc", "cord_analysis.cc", "cord_analysis.h", + "cord_buffer.cc", ], hdrs = [ "cord.h", + "cord_buffer.h", ], copts = ABSL_DEFAULT_COPTS, deps = [ @@ -702,6 +704,22 @@ cc_library( ) cc_test( + name = "cord_buffer_test", + size = "small", + srcs = ["cord_buffer_test.cc"], + copts = ABSL_TEST_COPTS, + visibility = ["//visibility:private"], + deps = [ + ":cord", + ":cord_internal", + ":cord_rep_test_util", + "//absl/base:config", + "//absl/types:span", + "@com_google_googletest//:gtest_main", + ], +) + +cc_test( name = "cord_test", size = "medium", srcs = ["cord_test.cc"], diff --git a/absl/strings/CMakeLists.txt b/absl/strings/CMakeLists.txt index a1b8d6ed..bb073301 100644 --- a/absl/strings/CMakeLists.txt +++ b/absl/strings/CMakeLists.txt @@ -845,10 +845,12 @@ absl_cc_library( cord HDRS "cord.h" + "cord_buffer.h" SRCS "cord.cc" "cord_analysis.cc" "cord_analysis.h" + "cord_buffer.cc" COPTS ${ABSL_DEFAULT_COPTS} DEPS diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc index c6ec1ecf..04dc7b90 100644 --- a/absl/strings/cord.cc +++ b/absl/strings/cord.cc @@ -34,6 +34,7 @@ #include "absl/base/port.h" #include "absl/container/fixed_array.h" #include "absl/container/inlined_vector.h" +#include "absl/strings/cord_buffer.h" #include "absl/strings/escaping.h" #include "absl/strings/internal/cord_data_edge.h" #include "absl/strings/internal/cord_internal.h" @@ -520,6 +521,46 @@ inline void Cord::AppendImpl(C&& src) { contents_.AppendTree(rep, CordzUpdateTracker::kAppendCord); } +static CordRep::ExtractResult ExtractAppendBuffer(CordRep* rep, + size_t min_capacity) { + switch (rep->tag) { + case cord_internal::BTREE: + return CordRepBtree::ExtractAppendBuffer(rep->btree(), min_capacity); + default: + if (rep->IsFlat() && rep->refcount.IsOne() && + rep->flat()->Capacity() - rep->length >= min_capacity) { + return {nullptr, rep}; + } + return {rep, nullptr}; + } +} + +static CordBuffer CreateAppendBuffer(InlineData& data, size_t capacity) { + // Watch out for overflow, people can ask for size_t::max(). + const size_t size = data.inline_size(); + capacity = (std::min)(std::numeric_limits<size_t>::max() - size, capacity); + CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(size + capacity); + cord_internal::SmallMemmove(buffer.data(), data.as_chars(), size); + buffer.SetLength(size); + data = {}; + return buffer; +} + +CordBuffer Cord::GetAppendBufferSlowPath(size_t capacity, size_t min_capacity) { + auto constexpr method = CordzUpdateTracker::kGetAppendBuffer; + CordRep* tree = contents_.tree(); + if (tree != nullptr) { + CordzUpdateScope scope(contents_.cordz_info(), method); + CordRep::ExtractResult result = ExtractAppendBuffer(tree, min_capacity); + if (result.extracted != nullptr) { + contents_.SetTreeOrEmpty(result.tree, scope); + return CordBuffer(result.extracted->flat()); + } + return CordBuffer::CreateWithDefaultLimit(capacity); + } + return CreateAppendBuffer(contents_.data_, capacity); +} + void Cord::Append(const Cord& src) { AppendImpl(src); } @@ -572,6 +613,33 @@ void Cord::PrependArray(absl::string_view src, MethodIdentifier method) { contents_.PrependTree(rep, method); } +void Cord::AppendPrecise(absl::string_view src, MethodIdentifier method) { + assert(!src.empty()); + assert(src.size() <= cord_internal::kMaxFlatLength); + if (contents_.remaining_inline_capacity() >= src.size()) { + const size_t inline_length = contents_.inline_size(); + memcpy(contents_.data_.as_chars() + inline_length, src.data(), src.size()); + contents_.set_inline_size(inline_length + src.size()); + } else { + contents_.AppendTree(CordRepFlat::Create(src), method); + } +} + +void Cord::PrependPrecise(absl::string_view src, MethodIdentifier method) { + assert(!src.empty()); + assert(src.size() <= cord_internal::kMaxFlatLength); + if (contents_.remaining_inline_capacity() >= src.size()) { + const size_t inline_length = contents_.inline_size(); + char data[InlineRep::kMaxInline + 1] = {0}; + memcpy(data, src.data(), src.size()); + memcpy(data + src.size(), contents_.data(), inline_length); + memcpy(contents_.data_.as_chars(), data, InlineRep::kMaxInline + 1); + contents_.set_inline_size(inline_length + src.size()); + } else { + contents_.PrependTree(CordRepFlat::Create(src), method); + } +} + template <typename T, Cord::EnableIfString<T>> inline void Cord::Prepend(T&& src) { if (src.size() <= kMaxBytesToCopy) { diff --git a/absl/strings/cord.h b/absl/strings/cord.h index 391b2c0b..f378dc07 100644 --- a/absl/strings/cord.h +++ b/absl/strings/cord.h @@ -80,6 +80,7 @@ #include "absl/functional/function_ref.h" #include "absl/meta/type_traits.h" #include "absl/strings/cord_analysis.h" +#include "absl/strings/cord_buffer.h" #include "absl/strings/internal/cord_data_edge.h" #include "absl/strings/internal/cord_internal.h" #include "absl/strings/internal/cord_rep_btree.h" @@ -244,6 +245,45 @@ class Cord { template <typename T, EnableIfString<T> = 0> void Append(T&& src); + // Appends `buffer` to this cord, unless `buffer` has a zero length in which + // case this method has no effect on this cord instance. + // This method is guaranteed to consume `buffer`. + void Append(CordBuffer buffer); + + // Returns a CordBuffer, re-using potential existing capacity in this cord. + // + // Cord instances may have additional unused capacity in the last (or first) + // nodes of the underlying tree to facilitate amortized growth. This method + // allows applications to explicitly use this spare capacity if available, + // or create a new CordBuffer instance otherwise. + // If this cord has a final non-shared node with at least `min_capacity` + // available, then this method will return that buffer including its data + // contents. I.e.; the returned buffer will have a non-zero length, and + // a capacity of at least `buffer.length + min_capacity`. Otherwise, this + // method will return `CordBuffer::CreateWithDefaultLimit(capacity)`. + // + // Below an example of using GetAppendBuffer. Notice that in this example we + // use `GetAppendBuffer()` only on the first iteration. As we know nothing + // about any initial extra capacity in `cord`, we may be able to use the extra + // capacity. But as we add new buffers with fully utilized contents after that + // we avoid calling `GetAppendBuffer()` on subsequent iterations: while this + // works fine, it results in an unnecessary inspection of cord contents: + // + // void AppendRandomDataToCord(absl::Cord &cord, size_t n) { + // bool first = true; + // while (n > 0) { + // CordBuffer buffer = first ? cord.GetAppendBuffer(n) + // : CordBuffer::CreateWithDefaultLimit(n); + // absl::Span<char> data = buffer.available_up_to(n); + // FillRandomValues(data.data(), data.size()); + // buffer.IncreaseLengthBy(data.size()); + // cord.Append(std::move(buffer)); + // n -= data.size(); + // first = false; + // } + // } + CordBuffer GetAppendBuffer(size_t capacity, size_t min_capacity = 16); + // Cord::Prepend() // // Prepends data to the Cord, which may come from another Cord or other string @@ -253,6 +293,11 @@ class Cord { template <typename T, EnableIfString<T> = 0> void Prepend(T&& src); + // Prepends `buffer` to this cord, unless `buffer` has a zero length in which + // case this method has no effect on this cord instance. + // This method is guaranteed to consume `buffer`. + void Prepend(CordBuffer buffer); + // Cord::RemovePrefix() // // Removes the first `n` bytes of a Cord. @@ -928,6 +973,15 @@ class Cord { template <typename C> void AppendImpl(C&& src); + // Appends / Prepends `src` to this instance, using precise sizing. + // This method does explicitly not attempt to use any spare capacity + // in any pending last added private owned flat. + // Requires `src` to be <= kMaxFlatLength. + void AppendPrecise(absl::string_view src, MethodIdentifier method); + void PrependPrecise(absl::string_view src, MethodIdentifier method); + + CordBuffer GetAppendBufferSlowPath(size_t capacity, size_t min_capacity); + // Prepends the provided data to this instance. `method` contains the public // API method for this action which is tracked for Cordz sampling purposes. void PrependArray(absl::string_view src, MethodIdentifier method); @@ -1284,6 +1338,31 @@ inline void Cord::Prepend(absl::string_view src) { PrependArray(src, CordzUpdateTracker::kPrependString); } +inline void Cord::Append(CordBuffer buffer) { + if (ABSL_PREDICT_FALSE(buffer.length() == 0)) return; + absl::string_view short_value; + if (CordRep* rep = buffer.ConsumeValue(short_value)) { + contents_.AppendTree(rep, CordzUpdateTracker::kAppendCordBuffer); + } else { + AppendPrecise(short_value, CordzUpdateTracker::kAppendCordBuffer); + } +} + +inline void Cord::Prepend(CordBuffer buffer) { + if (ABSL_PREDICT_FALSE(buffer.length() == 0)) return; + absl::string_view short_value; + if (CordRep* rep = buffer.ConsumeValue(short_value)) { + contents_.PrependTree(rep, CordzUpdateTracker::kPrependCordBuffer); + } else { + PrependPrecise(short_value, CordzUpdateTracker::kPrependCordBuffer); + } +} + +inline CordBuffer Cord::GetAppendBuffer(size_t capacity, size_t min_capacity) { + if (empty()) return CordBuffer::CreateWithDefaultLimit(capacity); + return GetAppendBufferSlowPath(capacity, min_capacity); +} + extern template void Cord::Append(std::string&& src); extern template void Cord::Prepend(std::string&& src); diff --git a/absl/strings/cord_buffer.cc b/absl/strings/cord_buffer.cc new file mode 100644 index 00000000..fd4045bd --- /dev/null +++ b/absl/strings/cord_buffer.cc @@ -0,0 +1,28 @@ +// Copyright 2022 The Abseil Authors +// +// 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 +// +// https://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 "absl/strings/cord_buffer.h" + +#include <cstddef> + +#include "absl/base/config.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN + +constexpr size_t CordBuffer::kDefaultLimit; +constexpr size_t CordBuffer::kCustomLimit; + +ABSL_NAMESPACE_END +} // namespace absl diff --git a/absl/strings/cord_buffer.h b/absl/strings/cord_buffer.h new file mode 100644 index 00000000..4f4bdc0e --- /dev/null +++ b/absl/strings/cord_buffer.h @@ -0,0 +1,571 @@ +// Copyright 2021 The Abseil Authors +// +// 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 +// +// https://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. +// +// ----------------------------------------------------------------------------- +// File: cord_buffer.h +// ----------------------------------------------------------------------------- +// +// This file defines an `absl::CordBuffer` data structure to hold data for +// eventual inclusion within an existing `Cord` data structure. Cord buffers are +// useful for building large Cords that may require custom allocation of its +// associated memory. +// +#ifndef ABSL_STRINGS_CORD_BUFFER_H_ +#define ABSL_STRINGS_CORD_BUFFER_H_ + +#include <algorithm> +#include <cassert> +#include <cstddef> +#include <cstdint> +#include <memory> +#include <utility> + +#include "absl/base/config.h" +#include "absl/numeric/bits.h" +#include "absl/strings/internal/cord_internal.h" +#include "absl/strings/internal/cord_rep_flat.h" +#include "absl/types/span.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN + +class Cord; +class CordBufferTestPeer; + +// CordBuffer +// +// CordBuffer manages memory buffers for purposes such as zero-copy APIs as well +// as applications building cords with large data requiring granular control +// over the allocation and size of cord data. For example, a function creating +// a cord of random data could use a CordBuffer as follows: +// +// absl::Cord CreateRandomCord(size_t length) { +// absl::Cord cord; +// while (length > 0) { +// CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(length); +// absl::Span<char> data = buffer.available_up_to(length); +// FillRandomValues(data.data(), data.size()); +// buffer.IncreaseLengthBy(data.size()); +// cord.Append(std::move(buffer)); +// length -= data.size(); +// } +// return cord; +// } +// +// CordBuffer instances are by default limited to a capacity of `kDefaultLimit` +// bytes. `kDefaultLimit` is currently just under 4KiB, but this default may +// change in the future and/or for specific architectures. The default limit is +// aimed to provide a good trade-off between performance and memory overhead. +// Smaller buffers typically incur more compute cost while larger buffers are +// more CPU efficient but create significant memory overhead because of such +// allocations being less granular. Using larger buffers may also increase the +// risk of memory fragmentation. +// +// Applications create a buffer using one of the `CreateWithDefaultLimit()` or +// `CreateWithCustomLimit()` methods. The returned instance will have a non-zero +// capacity and a zero length. Applications use the `data()` method to set the +// contents of the managed memory, and once done filling the buffer, use the +// `IncreaseLengthBy()` or 'SetLength()' method to specify the length of the +// initialized data before adding the buffer to a Cord. +// +// The `CreateWithCustomLimit()` method is intended for applications needing +// larger buffers than the default memory limit, allowing the allocation of up +// to a capacity of `kCustomLimit` bytes minus some minimum internal overhead. +// The usage of `CreateWithCustomLimit()` should be limited to only those use +// cases where the distribution of the input is relatively well known, and/or +// where the trade-off between the efficiency gains outweigh the risk of memory +// fragmentation. See the documentation for `CreateWithCustomLimit()` for more +// information on using larger custom limits. +// +// The capacity of a `CordBuffer` returned by one of the `Create` methods may +// be larger than the requested capacity due to rounding, alignment and +// granularity of the memory allocator. Applications should use the `capacity` +// method to obtain the effective capacity of the returned instance as +// demonstrated in the provided example above. +// +// CordBuffer is a move-only class. All references into the managed memory are +// invalidated when an instance is moved into either another CordBuffer instance +// or a Cord. Writing to a location obtained by a previous call to `data()` +// after an instance was moved will lead to undefined behavior. +// +// A `moved from` CordBuffer instance will have a valid, but empty state. +// CordBuffer is thread compatible. +class CordBuffer { + public: + // kDefaultLimit + // + // Default capacity limits of allocated CordBuffers. + // See the class comments for more information on allocation limits. + static constexpr size_t kDefaultLimit = cord_internal::kMaxFlatLength; + + // kCustomLimit + // + // Maximum size for CreateWithCustomLimit() allocated buffers. + // Note that the effective capacity may be slightly less + // because of internal overhead of internal cord buffers. + static constexpr size_t kCustomLimit = 64U << 10; + + // Constructors, Destructors and Assignment Operators + + // Creates an empty CordBuffer. + CordBuffer() = default; + + // Destroys this CordBuffer instance and, if not empty, releases any memory + // managed by this instance, invalidating previously returned references. + ~CordBuffer(); + + // CordBuffer is move-only + CordBuffer(CordBuffer&& rhs) noexcept; + CordBuffer& operator=(CordBuffer&&) noexcept; + CordBuffer(const CordBuffer&) = delete; + CordBuffer& operator=(const CordBuffer&) = delete; + + // CordBuffer::MaximumPayload() + // + // Returns the guaranteed maximum payload for a CordBuffer returned by the + // `CreateWithDefaultLimit()` method. While small, each internal buffer inside + // a Cord incurs an overhead to manage the length, type and reference count + // for the buffer managed inside the cord tree. Applications can use this + // method to get approximate number of buffers required for a given byte + // size, etc. + // + // For example: + // const size_t payload = absl::CordBuffer::MaximumPayload(); + // const size_t buffer_count = (total_size + payload - 1) / payload; + // buffers.reserve(buffer_count); + static constexpr size_t MaximumPayload(); + + // Overload to the above `MaximumPayload()` except that it returns the + // maximum payload for a CordBuffer returned by the `CreateWithCustomLimit()` + // method given the provided `block_size`. + static constexpr size_t MaximumPayload(size_t block_size); + + // CordBuffer::CreateWithDefaultLimit() + // + // Creates a CordBuffer instance of the desired `capacity`, capped at the + // default limit `kDefaultLimit`. The returned buffer has a guaranteed + // capacity of at least `min(kDefaultLimit, capacity)`. See the class comments + // for more information on buffer capacities and intended usage. + static CordBuffer CreateWithDefaultLimit(size_t capacity); + + + // CordBuffer::CreateWithCustomLimit() + // + // Creates a CordBuffer instance of the desired `capacity` rounded to an + // appropriate power of 2 size less than, or equal to `block_size`. + // Requires `block_size` to be a power of 2. + // + // If `capacity` is less than or equal to `kDefaultLimit`, then this method + // behaves identical to `CreateWithDefaultLimit`, which means that the caller + // is guaranteed to get a buffer of at least the requested capacity. + // + // If `capacity` is greater than or equal to `block_size`, then this method + // returns a buffer with an `allocated size` of `block_size` bytes. Otherwise, + // this methods returns a buffer with a suitable smaller power of 2 block size + // to satisfy the request. The actual size depends on a number of factors, and + // is typically (but not necessarily) the highest or second highest power of 2 + // value less than or equal to `capacity`. + // + // The 'allocated size' includes a small amount of overhead required for + // internal state, which is currently 13 bytes on 64-bit platforms. For + // example: a buffer created with `block_size` and `capacity' set to 8KiB + // will have an allocated size of 8KiB, and an effective internal `capacity` + // of 8KiB - 13 = 8179 bytes. + // + // To demonstrate this in practice, let's assume we want to read data from + // somewhat larger files using approximately 64KiB buffers: + // + // absl::Cord ReadFromFile(int fd, size_t n) { + // absl::Cord cord; + // while (n > 0) { + // CordBuffer buffer = CordBuffer::CreateWithCustomLimit(64 << 10, n); + // absl::Span<char> data = buffer.available_up_to(n); + // ReadFileDataOrDie(fd, data.data(), data.size()); + // buffer.IncreaseLengthBy(data.size()); + // cord.Append(std::move(buffer)); + // n -= data.size(); + // } + // return cord; + // } + // + // If we'd use this function to read a file of 659KiB, we may get the + // following pattern of allocated cord buffer sizes: + // + // CreateWithCustomLimit(64KiB, 674816) --> ~64KiB (65523) + // CreateWithCustomLimit(64KiB, 674816) --> ~64KiB (65523) + // ... + // CreateWithCustomLimit(64KiB, 19586) --> ~16KiB (16371) + // CreateWithCustomLimit(64KiB, 3215) --> 3215 (at least 3215) + // + // The reason the method returns a 16K buffer instead of a roughly 19K buffer + // is to reduce memory overhead and fragmentation risks. Using carefully + // chosen power of 2 values reduces the entropy of allocated memory sizes. + // + // Additionally, let's assume we'd use the above function on files that are + // generally smaller than 64K. If we'd use 'precise' sized buffers for such + // files, than we'd get a very wide distribution of allocated memory sizes + // rounded to 4K page sizes, and we'd end up with a lot of unused capacity. + // + // In general, application should only use custom sizes if the data they are + // consuming or storing is expected to be many times the chosen block size, + // and be based on objective data and performance metrics. For example, a + // compress function may work faster and consume less CPU when using larger + // buffers. Such an application should pick a size offering a reasonable + // trade-off between expected data size, compute savings with larger buffers, + // and the cost or fragmentation effect of larger buffers. + // Applications must pick a reasonable spot on that curve, and make sure their + // data meets their expectations in size distributions such as "mostly large". + static CordBuffer CreateWithCustomLimit(size_t block_size, size_t capacity); + + // CordBuffer::available() + // + // Returns the span delineating the available capacity in this buffer + // which is defined as `{ data() + length(), capacity() - length() }`. + absl::Span<char> available(); + + // CordBuffer::available_up_to() + // + // Returns the span delineating the available capacity in this buffer limited + // to `size` bytes. This is equivalent to `available().subspan(0, size)`. + absl::Span<char> available_up_to(size_t size); + + // CordBuffer::data() + // + // Returns a non-null reference to the data managed by this instance. + // Applications are allowed to write up to `capacity` bytes of instance data. + // CordBuffer data is uninitialized by default. Reading data from an instance + // that has not yet been initialized will lead to undefined behavior. + char* data(); + const char* data() const; + + // CordBuffer::length() + // + // Returns the length of this instance. The default length of a CordBuffer is + // 0, indicating an 'empty' CordBuffer. Applications must specify the length + // of the data in a CordBuffer before adding it to a Cord. + size_t length() const; + + // CordBuffer::capacity() + // + // Returns the capacity of this instance. All instances have a non-zero + // capacity: default and `moved from` instances have a small internal buffer. + size_t capacity() const; + + // CordBuffer::IncreaseLengthBy() + // + // Increases the length of this buffer by the specified 'n' bytes. + // Applications must make sure all data in this buffer up to the new length + // has been initialized before adding a CordBuffer to a Cord: failure to do so + // will lead to undefined behavior. Requires `length() + n <= capacity()`. + // Typically, applications will use 'available_up_to()` to get a span of the + // desired capacity, and use `span.size()` to increase the length as in: + // absl::Span<char> span = buffer.available_up_to(desired); + // buffer.IncreaseLengthBy(span.size()); + // memcpy(span.data(), src, span.size()); + // etc... + void IncreaseLengthBy(size_t n); + + // CordBuffer::SetLength() + // + // Sets the data length of this instance. Applications must make sure all data + // of the specified length has been initialized before adding a CordBuffer to + // a Cord: failure to do so will lead to undefined behavior. + // Setting the length to a small value or zero does not release any memory + // held by this CordBuffer instance. Requires `length <= capacity()`. + // Applications should preferably use the `IncreaseLengthBy()` method above + // in combination with the 'available()` or `available_up_to()` methods. + void SetLength(size_t length); + + private: + // Make sure we don't accidentally over promise. + static_assert(kCustomLimit <= cord_internal::kMaxLargeFlatSize, ""); + + // Assume the cost of an 'uprounded' allocation to CeilPow2(size) versus + // the cost of allocating at least 1 extra flat <= 4KB: + // - Flat overhead = 13 bytes + // - Btree amortized cost / node =~ 13 bytes + // - 64 byte granularity of tcmalloc at 4K =~ 32 byte average + // CPU cost and efficiency requires we should at least 'save' something by + // splitting, as a poor man's measure, we say the slop needs to be + // at least double the cost offset to make it worth splitting: ~128 bytes. + static constexpr size_t kMaxPageSlop = 128; + + // Overhead for allocation a flat. + static constexpr size_t kOverhead = cord_internal::kFlatOverhead; + + using CordRepFlat = cord_internal::CordRepFlat; + + // `Rep` is the internal data representation of a CordBuffer. The internal + // representation has an internal small size optimization similar to + // std::string (SSO). + struct Rep { + // Inline SSO size of a CordBuffer + static constexpr size_t kInlineCapacity = sizeof(intptr_t) * 2 - 1; + + // Creates a default instance with kInlineCapacity. + Rep() : short_rep{} {} + + // Creates an instance managing an allocated non zero CordRep. + explicit Rep(cord_internal::CordRepFlat* rep) : long_rep{rep} { + assert(rep != nullptr); + } + + // Returns true if this instance manages the SSO internal buffer. + bool is_short() const { + constexpr size_t offset = offsetof(Short, raw_size); + return (reinterpret_cast<const char*>(this)[offset] & 1) != 0; + } + + // Returns the available area of the internal SSO data + absl::Span<char> short_available() { + assert(is_short()); + const size_t length = (short_rep.raw_size >> 1); + return absl::Span<char>(short_rep.data + length, + kInlineCapacity - length); + } + + // Returns the available area of the internal SSO data + absl::Span<char> long_available() { + assert(!is_short()); + const size_t length = long_rep.rep->length; + return absl::Span<char>(long_rep.rep->Data() + length, + long_rep.rep->Capacity() - length); + } + + // Returns the length of the internal SSO data. + size_t short_length() const { + assert(is_short()); + return short_rep.raw_size >> 1; + } + + // Sets the length of the internal SSO data. + // Disregards any previously set CordRep instance. + void set_short_length(size_t length) { + short_rep.raw_size = static_cast<char>((length << 1) + 1); + } + + // Adds `n` to the current short length. + void add_short_length(size_t n) { + assert(is_short()); + short_rep.raw_size += static_cast<char>(n << 1); + } + + // Returns reference to the internal SSO data buffer. + char* data() { + assert(is_short()); + return short_rep.data; + } + const char* data() const { + assert(is_short()); + return short_rep.data; + } + + // Returns a pointer the external CordRep managed by this instance. + cord_internal::CordRepFlat* rep() const { + assert(!is_short()); + return long_rep.rep; + } + + // The internal representation takes advantage of the fact that allocated + // memory is always on an even address, and uses the least significant bit + // of the first or last byte (depending on endianness) as the inline size + // indicator overlapping with the least significant byte of the CordRep*. +#if defined(ABSL_IS_BIG_ENDIAN) + struct Long { + explicit Long(cord_internal::CordRepFlat* rep_arg) : rep(rep_arg) {} + void* padding; + cord_internal::CordRepFlat* rep; + }; + struct Short { + char data[sizeof(Long) - 1]; + char raw_size = 1; + }; +#else + struct Long { + explicit Long(cord_internal::CordRepFlat* rep_arg) : rep(rep_arg) {} + cord_internal::CordRepFlat* rep; + void* padding; + }; + struct Short { + char raw_size = 1; + char data[sizeof(Long) - 1]; + }; +#endif + + union { + Long long_rep; + Short short_rep; + }; + }; + + // Power2 functions + static bool IsPow2(size_t size) { return absl::has_single_bit(size); } + static size_t Log2Floor(size_t size) { return absl::bit_width(size) - 1; } + static size_t Log2Ceil(size_t size) { return absl::bit_width(size - 1); } + + // Implementation of `CreateWithCustomLimit()`. + // This implementation allows for future memory allocation hints to + // be passed down into the CordRepFlat allocation function. + template <typename... AllocationHints> + static CordBuffer CreateWithCustomLimitImpl(size_t block_size, + size_t capacity, + AllocationHints... hints); + + // Consumes the value contained in this instance and resets the instance. + // This method returns a non-null Cordrep* if the current instances manages a + // CordRep*, and resets the instance to an empty SSO instance. If the current + // instance is an SSO instance, then this method returns nullptr and sets + // `short_value` to the inlined data value. In either case, the current + // instance length is reset to zero. + // This method is intended to be used by Cord internal functions only. + cord_internal::CordRep* ConsumeValue(absl::string_view& short_value) { + cord_internal::CordRep* rep = nullptr; + if (rep_.is_short()) { + short_value = absl::string_view(rep_.data(), rep_.short_length()); + } else { + rep = rep_.rep(); + } + rep_.set_short_length(0); + return rep; + } + + // Internal constructor. + explicit CordBuffer(cord_internal::CordRepFlat* rep) : rep_(rep) { + assert(rep != nullptr); + } + + Rep rep_; + + friend class Cord; + friend class CordBufferTestPeer; +}; + +inline constexpr size_t CordBuffer::MaximumPayload() { + return cord_internal::kMaxFlatLength; +} + +inline constexpr size_t CordBuffer::MaximumPayload(size_t block_size) { + // TODO(absl-team): Use std::min when C++11 support is dropped. + return (kCustomLimit < block_size ? kCustomLimit : block_size) - + cord_internal::kFlatOverhead; +} + +inline CordBuffer CordBuffer::CreateWithDefaultLimit(size_t capacity) { + if (capacity > Rep::kInlineCapacity) { + auto* rep = cord_internal::CordRepFlat::New(capacity); + rep->length = 0; + return CordBuffer(rep); + } + return CordBuffer(); +} + +template <typename... AllocationHints> +inline CordBuffer CordBuffer::CreateWithCustomLimitImpl( + size_t block_size, size_t capacity, AllocationHints... hints) { + assert(IsPow2(block_size)); + capacity = (std::min)(capacity, kCustomLimit); + block_size = (std::min)(block_size, kCustomLimit); + if (capacity + kOverhead >= block_size) { + capacity = block_size; + } else if (capacity <= kDefaultLimit) { + capacity = capacity + kOverhead; + } else if (!IsPow2(capacity)) { + // Check if rounded up to next power 2 is a good enough fit + // with limited waste making it an acceptable direct fit. + const size_t rounded_up = size_t{1} << Log2Ceil(capacity); + const size_t slop = rounded_up - capacity; + if (slop >= kOverhead && slop <= kMaxPageSlop + kOverhead) { + capacity = rounded_up; + } else { + // Round down to highest power of 2 <= capacity. + // Consider a more aggressive step down if that may reduce the + // risk of fragmentation where 'people are holding it wrong'. + const size_t rounded_down = size_t{1} << Log2Floor(capacity); + capacity = rounded_down; + } + } + const size_t length = capacity - kOverhead; + auto* rep = CordRepFlat::New(CordRepFlat::Large(), length, hints...); + rep->length = 0; + return CordBuffer(rep); +} + +inline CordBuffer CordBuffer::CreateWithCustomLimit(size_t block_size, + size_t capacity) { + return CreateWithCustomLimitImpl(block_size, capacity); +} + +inline CordBuffer::~CordBuffer() { + if (!rep_.is_short()) { + cord_internal::CordRepFlat::Delete(rep_.rep()); + } +} + +inline CordBuffer::CordBuffer(CordBuffer&& rhs) noexcept : rep_(rhs.rep_) { + rhs.rep_.set_short_length(0); +} + +inline CordBuffer& CordBuffer::operator=(CordBuffer&& rhs) noexcept { + if (!rep_.is_short()) cord_internal::CordRepFlat::Delete(rep_.rep()); + rep_ = rhs.rep_; + rhs.rep_.set_short_length(0); + return *this; +} + +inline absl::Span<char> CordBuffer::available() { + return rep_.is_short() ? rep_.short_available() : rep_.long_available(); +} + +inline absl::Span<char> CordBuffer::available_up_to(size_t size) { + return available().subspan(0, size); +} + +inline char* CordBuffer::data() { + return rep_.is_short() ? rep_.data() : rep_.rep()->Data(); +} + +inline const char* CordBuffer::data() const { + return rep_.is_short() ? rep_.data() : rep_.rep()->Data(); +} + +inline size_t CordBuffer::capacity() const { + return rep_.is_short() ? Rep::kInlineCapacity : rep_.rep()->Capacity(); +} + +inline size_t CordBuffer::length() const { + return rep_.is_short() ? rep_.short_length() : rep_.rep()->length; +} + +inline void CordBuffer::SetLength(size_t length) { + assert(length <= capacity()); + if (rep_.is_short()) { + rep_.set_short_length(length); + } else { + rep_.rep()->length = length; + } +} + +inline void CordBuffer::IncreaseLengthBy(size_t n) { + assert(n <= capacity() && length() + n <= capacity()); + if (rep_.is_short()) { + rep_.add_short_length(n); + } else { + rep_.rep()->length += n; + } +} + +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_STRINGS_CORD_BUFFER_H_ diff --git a/absl/strings/cord_buffer_test.cc b/absl/strings/cord_buffer_test.cc new file mode 100644 index 00000000..5c7437ae --- /dev/null +++ b/absl/strings/cord_buffer_test.cc @@ -0,0 +1,320 @@ +// Copyright 2021 The Abseil Authors +// +// 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 +// +// https://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 "absl/strings/cord_buffer.h" + + +#include <algorithm> +#include <climits> +#include <cstring> +#include <string> +#include <utility> + +#include "gmock/gmock.h" +#include "gtest/gtest.h" +#include "absl/base/config.h" +#include "absl/strings/internal/cord_rep_flat.h" +#include "absl/strings/internal/cord_rep_test_util.h" +#include "absl/types/span.h" + +using testing::Eq; +using testing::Ge; +using testing::Le; +using testing::Ne; + +namespace absl { +ABSL_NAMESPACE_BEGIN + +class CordBufferTestPeer { + public: + static cord_internal::CordRep* ConsumeValue(CordBuffer& buffer, + absl::string_view& short_value) { + return buffer.ConsumeValue(short_value); + } +}; + +namespace { + +using ::absl::cordrep_testing::CordToString; + +constexpr size_t kInlinedSize = sizeof(CordBuffer) - 1; +constexpr size_t kDefaultLimit = CordBuffer::kDefaultLimit; +constexpr size_t kCustomLimit = CordBuffer::kCustomLimit; +constexpr size_t kMaxFlatSize = cord_internal::kMaxFlatSize; +constexpr size_t kMaxFlatLength = cord_internal::kMaxFlatLength; +constexpr size_t kFlatOverhead = cord_internal::kFlatOverhead; + +constexpr size_t k8KiB = 8 << 10; +constexpr size_t k16KiB = 16 << 10; +constexpr size_t k64KiB = 64 << 10; +constexpr size_t k1MB = 1 << 20; + +class CordBufferTest : public testing::TestWithParam<size_t> {}; + +INSTANTIATE_TEST_SUITE_P(MediumSize, CordBufferTest, + testing::Values(1, kInlinedSize - 1, kInlinedSize, + kInlinedSize + 1, kDefaultLimit - 1, + kDefaultLimit)); + +TEST_P(CordBufferTest, MaximumPayload) { + EXPECT_THAT(CordBuffer::MaximumPayload(), Eq(kMaxFlatLength)); + EXPECT_THAT(CordBuffer::MaximumPayload(512), Eq(512 - kFlatOverhead)); + EXPECT_THAT(CordBuffer::MaximumPayload(k64KiB), Eq(k64KiB - kFlatOverhead)); + EXPECT_THAT(CordBuffer::MaximumPayload(k1MB), Eq(k64KiB - kFlatOverhead)); +} + +TEST(CordBufferTest, ConstructDefault) { + CordBuffer buffer; + EXPECT_THAT(buffer.capacity(), Eq(sizeof(CordBuffer) - 1)); + EXPECT_THAT(buffer.length(), Eq(0)); + EXPECT_THAT(buffer.data(), Ne(nullptr)); + EXPECT_THAT(buffer.available().data(), Eq(buffer.data())); + EXPECT_THAT(buffer.available().size(), Eq(buffer.capacity())); + memset(buffer.data(), 0xCD, buffer.capacity()); +} + +TEST(CordBufferTest, CreateSsoWithDefaultLimit) { + CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(3); + EXPECT_THAT(buffer.capacity(), Ge(3)); + EXPECT_THAT(buffer.capacity(), Le(sizeof(CordBuffer))); + EXPECT_THAT(buffer.length(), Eq(0)); + memset(buffer.data(), 0xCD, buffer.capacity()); + + memcpy(buffer.data(), "Abc", 3); + buffer.SetLength(3); + EXPECT_THAT(buffer.length(), Eq(3)); + absl::string_view short_value; + EXPECT_THAT(CordBufferTestPeer::ConsumeValue(buffer, short_value), + Eq(nullptr)); + EXPECT_THAT(absl::string_view(buffer.data(), 3), Eq("Abc")); + EXPECT_THAT(short_value, Eq("Abc")); +} + +TEST_P(CordBufferTest, Available) { + const size_t requested = GetParam(); + CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(requested); + EXPECT_THAT(buffer.available().data(), Eq(buffer.data())); + EXPECT_THAT(buffer.available().size(), Eq(buffer.capacity())); + + buffer.SetLength(2); + EXPECT_THAT(buffer.available().data(), Eq(buffer.data() + 2)); + EXPECT_THAT(buffer.available().size(), Eq(buffer.capacity() - 2)); +} + +TEST_P(CordBufferTest, IncreaseLengthBy) { + const size_t requested = GetParam(); + CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(requested); + buffer.IncreaseLengthBy(2); + EXPECT_THAT(buffer.length(), Eq(2)); + buffer.IncreaseLengthBy(5); + EXPECT_THAT(buffer.length(), Eq(7)); +} + +TEST_P(CordBufferTest, AvailableUpTo) { + const size_t requested = GetParam(); + CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(requested); + size_t expected_up_to = std::min<size_t>(3, buffer.capacity()); + EXPECT_THAT(buffer.available_up_to(3).data(), Eq(buffer.data())); + EXPECT_THAT(buffer.available_up_to(3).size(), Eq(expected_up_to)); + + buffer.SetLength(2); + expected_up_to = std::min<size_t>(3, buffer.capacity() - 2); + EXPECT_THAT(buffer.available_up_to(3).data(), Eq(buffer.data() + 2)); + EXPECT_THAT(buffer.available_up_to(3).size(), Eq(expected_up_to)); +} + +// Returns the maximum capacity for a given block_size and requested size. +size_t MaxCapacityFor(size_t block_size, size_t requested) { + requested = (std::min)(requested, cord_internal::kMaxLargeFlatSize); + // Maximum returned size is always capped at block_size - kFlatOverhead. + return block_size - kFlatOverhead; +} + +TEST_P(CordBufferTest, CreateWithDefaultLimit) { + const size_t requested = GetParam(); + CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(requested); + EXPECT_THAT(buffer.capacity(), Ge(requested)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(kMaxFlatSize, requested))); + EXPECT_THAT(buffer.length(), Eq(0)); + + memset(buffer.data(), 0xCD, buffer.capacity()); + + std::string data(requested - 1, 'x'); + memcpy(buffer.data(), data.c_str(), requested); + buffer.SetLength(requested); + + EXPECT_THAT(buffer.length(), Eq(requested)); + EXPECT_THAT(absl::string_view(buffer.data()), Eq(data)); +} + +TEST(CordBufferTest, CreateWithDefaultLimitAskingFor2GB) { + constexpr size_t k2GiB = 1U << 31; + CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(k2GiB); + // Expect to never be awarded more than a reasonable memory size, even in + // cases where a (debug) memory allocator may grant us somewhat more memory + // than `kDefaultLimit` which should be no more than `2 * kDefaultLimit` + EXPECT_THAT(buffer.capacity(), Le(2 * CordBuffer::kDefaultLimit)); + EXPECT_THAT(buffer.length(), Eq(0)); + EXPECT_THAT(buffer.data(), Ne(nullptr)); + memset(buffer.data(), 0xCD, buffer.capacity()); +} + +TEST_P(CordBufferTest, MoveConstruct) { + const size_t requested = GetParam(); + CordBuffer from = CordBuffer::CreateWithDefaultLimit(requested); + const size_t capacity = from.capacity(); + memcpy(from.data(), "Abc", 4); + from.SetLength(4); + + CordBuffer to(std::move(from)); + EXPECT_THAT(to.capacity(), Eq(capacity)); + EXPECT_THAT(to.length(), Eq(4)); + EXPECT_THAT(absl::string_view(to.data()), Eq("Abc")); + + EXPECT_THAT(from.length(), Eq(0)); // NOLINT +} + +TEST_P(CordBufferTest, MoveAssign) { + const size_t requested = GetParam(); + CordBuffer from = CordBuffer::CreateWithDefaultLimit(requested); + const size_t capacity = from.capacity(); + memcpy(from.data(), "Abc", 4); + from.SetLength(4); + + CordBuffer to; + to = std::move(from); + EXPECT_THAT(to.capacity(), Eq(capacity)); + EXPECT_THAT(to.length(), Eq(4)); + EXPECT_THAT(absl::string_view(to.data()), Eq("Abc")); + + EXPECT_THAT(from.length(), Eq(0)); // NOLINT +} + +TEST_P(CordBufferTest, ConsumeValue) { + const size_t requested = GetParam(); + CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(requested); + memcpy(buffer.data(), "Abc", 4); + buffer.SetLength(3); + + absl::string_view short_value; + if (cord_internal::CordRep* rep = + CordBufferTestPeer::ConsumeValue(buffer, short_value)) { + EXPECT_THAT(CordToString(rep), Eq("Abc")); + cord_internal::CordRep::Unref(rep); + } else { + EXPECT_THAT(short_value, Eq("Abc")); + } + EXPECT_THAT(buffer.length(), Eq(0)); +} + +TEST_P(CordBufferTest, CreateWithCustomLimitWithinDefaultLimit) { + const size_t requested = GetParam(); + CordBuffer buffer = + CordBuffer::CreateWithCustomLimit(kMaxFlatSize, requested); + EXPECT_THAT(buffer.capacity(), Ge(requested)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(kMaxFlatSize, requested))); + EXPECT_THAT(buffer.length(), Eq(0)); + + memset(buffer.data(), 0xCD, buffer.capacity()); + + std::string data(requested - 1, 'x'); + memcpy(buffer.data(), data.c_str(), requested); + buffer.SetLength(requested); + + EXPECT_THAT(buffer.length(), Eq(requested)); + EXPECT_THAT(absl::string_view(buffer.data()), Eq(data)); +} + +TEST(CordLargeBufferTest, CreateAtOrBelowDefaultLimit) { + CordBuffer buffer = CordBuffer::CreateWithCustomLimit(k64KiB, kDefaultLimit); + EXPECT_THAT(buffer.capacity(), Ge(kDefaultLimit)); + EXPECT_THAT(buffer.capacity(), + Le(MaxCapacityFor(kMaxFlatSize, kDefaultLimit))); + + buffer = CordBuffer::CreateWithCustomLimit(k64KiB, 3178); + EXPECT_THAT(buffer.capacity(), Ge(3178)); +} + +TEST(CordLargeBufferTest, CreateWithCustomLimit) { + ASSERT_THAT((kMaxFlatSize & (kMaxFlatSize - 1)) == 0, "Must be power of 2"); + + for (size_t size = kMaxFlatSize; size <= kCustomLimit; size *= 2) { + CordBuffer buffer = CordBuffer::CreateWithCustomLimit(size, size); + size_t expected = size - kFlatOverhead; + ASSERT_THAT(buffer.capacity(), Ge(expected)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(size, expected))); + } +} + +TEST(CordLargeBufferTest, CreateWithTooLargeLimit) { + CordBuffer buffer = CordBuffer::CreateWithCustomLimit(k64KiB, k1MB); + ASSERT_THAT(buffer.capacity(), Ge(k64KiB - kFlatOverhead)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(k64KiB, k1MB))); +} + +TEST(CordLargeBufferTest, CreateWithHugeValueForOverFlowHardening) { + for (size_t dist_from_max = 0; dist_from_max <= 32; ++dist_from_max) { + size_t capacity = std::numeric_limits<size_t>::max() - dist_from_max; + + CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(capacity); + ASSERT_THAT(buffer.capacity(), Ge(kDefaultLimit)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(kMaxFlatSize, capacity))); + + for (size_t limit = kMaxFlatSize; limit <= kCustomLimit; limit *= 2) { + CordBuffer buffer = CordBuffer::CreateWithCustomLimit(limit, capacity); + ASSERT_THAT(buffer.capacity(), Ge(limit - kFlatOverhead)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(limit, capacity))); + } + } +} + +TEST(CordLargeBufferTest, CreateWithSmallLimit) { + CordBuffer buffer = CordBuffer::CreateWithCustomLimit(512, 1024); + ASSERT_THAT(buffer.capacity(), Ge(512 - kFlatOverhead)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(512, 1024))); + + // Ask for precise block size, should return size - kOverhead + buffer = CordBuffer::CreateWithCustomLimit(512, 512); + ASSERT_THAT(buffer.capacity(), Ge(512 - kFlatOverhead)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(512, 512))); + + // Corner case: 511 < block_size, but 511 + kOverhead is above + buffer = CordBuffer::CreateWithCustomLimit(512, 511); + ASSERT_THAT(buffer.capacity(), Ge(512 - kFlatOverhead)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(512, 511))); + + // Corner case: 498 + kOverhead < block_size + buffer = CordBuffer::CreateWithCustomLimit(512, 498); + ASSERT_THAT(buffer.capacity(), Ge(512 - kFlatOverhead)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(512, 498))); +} + +TEST(CordLargeBufferTest, CreateWasteFull) { + // 15 KiB gets rounded down to next pow2 value. + const size_t requested = (15 << 10); + CordBuffer buffer = CordBuffer::CreateWithCustomLimit(k16KiB, requested); + ASSERT_THAT(buffer.capacity(), Ge(k8KiB - kFlatOverhead)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(k8KiB, requested))); +} + +TEST(CordLargeBufferTest, CreateSmallSlop) { + const size_t requested = k16KiB - 2 * kFlatOverhead; + CordBuffer buffer = CordBuffer::CreateWithCustomLimit(k16KiB, requested); + ASSERT_THAT(buffer.capacity(), Ge(k16KiB - kFlatOverhead)); + EXPECT_THAT(buffer.capacity(), Le(MaxCapacityFor(k16KiB, requested))); +} + +} // namespace +ABSL_NAMESPACE_END +} // namespace absl diff --git a/absl/strings/cord_test.cc b/absl/strings/cord_test.cc index 4261c99a..0862f69a 100644 --- a/absl/strings/cord_test.cc +++ b/absl/strings/cord_test.cc @@ -597,6 +597,284 @@ TEST_P(CordTest, CopyToString) { "copying ", "to ", "a ", "string."}))); } +TEST_P(CordTest, AppendEmptyBuffer) { + absl::Cord cord; + cord.Append(absl::CordBuffer()); + cord.Append(absl::CordBuffer::CreateWithDefaultLimit(2000)); +} + +TEST_P(CordTest, AppendEmptyBufferToFlat) { + absl::Cord cord(std::string(2000, 'x')); + cord.Append(absl::CordBuffer()); + cord.Append(absl::CordBuffer::CreateWithDefaultLimit(2000)); +} + +TEST_P(CordTest, AppendEmptyBufferToTree) { + absl::Cord cord(std::string(2000, 'x')); + cord.Append(std::string(2000, 'y')); + cord.Append(absl::CordBuffer()); + cord.Append(absl::CordBuffer::CreateWithDefaultLimit(2000)); +} + +TEST_P(CordTest, AppendSmallBuffer) { + absl::Cord cord; + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(3); + ASSERT_THAT(buffer.capacity(), ::testing::Le(15)); + memcpy(buffer.data(), "Abc", 3); + buffer.SetLength(3); + cord.Append(std::move(buffer)); + EXPECT_EQ(buffer.length(), 0); // NOLINT + EXPECT_GT(buffer.capacity(), 0); // NOLINT + + buffer = absl::CordBuffer::CreateWithDefaultLimit(3); + memcpy(buffer.data(), "defgh", 5); + buffer.SetLength(5); + cord.Append(std::move(buffer)); + EXPECT_EQ(buffer.length(), 0); // NOLINT + EXPECT_GT(buffer.capacity(), 0); // NOLINT + + EXPECT_THAT(cord.Chunks(), ::testing::ElementsAre("Abcdefgh")); +} + +TEST_P(CordTest, AppendAndPrependBufferArePrecise) { + // Create a cord large enough to force 40KB flats. + std::string test_data(absl::cord_internal::kMaxFlatLength * 10, 'x'); + absl::Cord cord1(test_data); + absl::Cord cord2(test_data); + const size_t size1 = cord1.EstimatedMemoryUsage(); + const size_t size2 = cord2.EstimatedMemoryUsage(); + + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(3); + memcpy(buffer.data(), "Abc", 3); + buffer.SetLength(3); + cord1.Append(std::move(buffer)); + + buffer = absl::CordBuffer::CreateWithDefaultLimit(3); + memcpy(buffer.data(), "Abc", 3); + buffer.SetLength(3); + cord2.Prepend(std::move(buffer)); + +#ifndef NDEBUG + // Allow 32 bytes new CordRepFlat, and 128 bytes for 'glue nodes' + constexpr size_t kMaxDelta = 128 + 32; +#else + // Allow 256 bytes extra for 'allocation debug overhead' + constexpr size_t kMaxDelta = 128 + 32 + 256; +#endif + + EXPECT_LE(cord1.EstimatedMemoryUsage() - size1, kMaxDelta); + EXPECT_LE(cord2.EstimatedMemoryUsage() - size2, kMaxDelta); + + EXPECT_EQ(cord1, absl::StrCat(test_data, "Abc")); + EXPECT_EQ(cord2, absl::StrCat("Abc", test_data)); +} + +TEST_P(CordTest, PrependSmallBuffer) { + absl::Cord cord; + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(3); + ASSERT_THAT(buffer.capacity(), ::testing::Le(15)); + memcpy(buffer.data(), "Abc", 3); + buffer.SetLength(3); + cord.Prepend(std::move(buffer)); + EXPECT_EQ(buffer.length(), 0); // NOLINT + EXPECT_GT(buffer.capacity(), 0); // NOLINT + + buffer = absl::CordBuffer::CreateWithDefaultLimit(3); + memcpy(buffer.data(), "defgh", 5); + buffer.SetLength(5); + cord.Prepend(std::move(buffer)); + EXPECT_EQ(buffer.length(), 0); // NOLINT + EXPECT_GT(buffer.capacity(), 0); // NOLINT + + EXPECT_THAT(cord.Chunks(), ::testing::ElementsAre("defghAbc")); +} + +TEST_P(CordTest, AppendLargeBuffer) { + absl::Cord cord; + + std::string s1(700, '1'); + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(s1.size()); + memcpy(buffer.data(), s1.data(), s1.size()); + buffer.SetLength(s1.size()); + cord.Append(std::move(buffer)); + EXPECT_EQ(buffer.length(), 0); // NOLINT + EXPECT_GT(buffer.capacity(), 0); // NOLINT + + std::string s2(1000, '2'); + buffer = absl::CordBuffer::CreateWithDefaultLimit(s2.size()); + memcpy(buffer.data(), s2.data(), s2.size()); + buffer.SetLength(s2.size()); + cord.Append(std::move(buffer)); + EXPECT_EQ(buffer.length(), 0); // NOLINT + EXPECT_GT(buffer.capacity(), 0); // NOLINT + + EXPECT_THAT(cord.Chunks(), ::testing::ElementsAre(s1, s2)); +} + +TEST_P(CordTest, PrependLargeBuffer) { + absl::Cord cord; + + std::string s1(700, '1'); + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(s1.size()); + memcpy(buffer.data(), s1.data(), s1.size()); + buffer.SetLength(s1.size()); + cord.Prepend(std::move(buffer)); + EXPECT_EQ(buffer.length(), 0); // NOLINT + EXPECT_GT(buffer.capacity(), 0); // NOLINT + + std::string s2(1000, '2'); + buffer = absl::CordBuffer::CreateWithDefaultLimit(s2.size()); + memcpy(buffer.data(), s2.data(), s2.size()); + buffer.SetLength(s2.size()); + cord.Prepend(std::move(buffer)); + EXPECT_EQ(buffer.length(), 0); // NOLINT + EXPECT_GT(buffer.capacity(), 0); // NOLINT + + EXPECT_THAT(cord.Chunks(), ::testing::ElementsAre(s2, s1)); +} + +TEST_P(CordTest, GetAppendBufferOnEmptyCord) { + absl::Cord cord; + absl::CordBuffer buffer = cord.GetAppendBuffer(1000); + EXPECT_GE(buffer.capacity(), 1000); + EXPECT_EQ(buffer.length(), 0); +} + +TEST_P(CordTest, GetAppendBufferOnInlinedCord) { + static constexpr int kInlinedSize = sizeof(absl::CordBuffer) - 1; + for (int size : {6, kInlinedSize - 3, kInlinedSize - 2, 1000}) { + absl::Cord cord("Abc"); + absl::CordBuffer buffer = cord.GetAppendBuffer(size, 1); + EXPECT_GE(buffer.capacity(), 3 + size); + EXPECT_EQ(buffer.length(), 3); + EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), "Abc"); + EXPECT_TRUE(cord.empty()); + } +} + +TEST_P(CordTest, GetAppendBufferOnInlinedCordWithCapacityCloseToMax) { + // Cover the use case where we have a non empty inlined cord with some size + // 'n', and ask for something like 'uint64_max - k', assuming internal logic + // could overflow on 'uint64_max - k + size', and return a valid, but + // inefficiently smaller buffer if it would provide is the max allowed size. + for (size_t dist_from_max = 0; dist_from_max <= 4; ++dist_from_max) { + absl::Cord cord("Abc"); + size_t size = std::numeric_limits<size_t>::max() - dist_from_max; + absl::CordBuffer buffer = cord.GetAppendBuffer(size, 1); + EXPECT_EQ(buffer.capacity(), absl::CordBuffer::kDefaultLimit); + EXPECT_EQ(buffer.length(), 3); + EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), "Abc"); + EXPECT_TRUE(cord.empty()); + } +} + +TEST_P(CordTest, GetAppendBufferOnFlat) { + // Create a cord with a single flat and extra capacity + absl::Cord cord; + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500); + buffer.SetLength(3); + memcpy(buffer.data(), "Abc", 3); + cord.Append(std::move(buffer)); + + buffer = cord.GetAppendBuffer(6); + EXPECT_GE(buffer.capacity(), 500); + EXPECT_EQ(buffer.length(), 3); + EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), "Abc"); + EXPECT_TRUE(cord.empty()); +} + +TEST_P(CordTest, GetAppendBufferOnFlatWithoutMinCapacity) { + // Create a cord with a single flat and extra capacity + absl::Cord cord; + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500); + buffer.SetLength(30); + memset(buffer.data(), 'x', 30); + cord.Append(std::move(buffer)); + + buffer = cord.GetAppendBuffer(1000, 900); + EXPECT_GE(buffer.capacity(), 1000); + EXPECT_EQ(buffer.length(), 0); + EXPECT_EQ(cord, std::string(30, 'x')); +} + +TEST_P(CordTest, GetAppendBufferOnTree) { + RandomEngine rng; + for (int num_flats : {2, 3, 100}) { + // Create a cord with `num_flats` flats and extra capacity + absl::Cord cord; + std::string prefix; + std::string last; + for (int i = 0; i < num_flats - 1; ++i) { + prefix += last; + last = RandomLowercaseString(&rng, 10); + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500); + buffer.SetLength(10); + memcpy(buffer.data(), last.data(), 10); + cord.Append(std::move(buffer)); + } + absl::CordBuffer buffer = cord.GetAppendBuffer(6); + EXPECT_GE(buffer.capacity(), 500); + EXPECT_EQ(buffer.length(), 10); + EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), last); + EXPECT_EQ(cord, prefix); + } +} + +TEST_P(CordTest, GetAppendBufferOnTreeWithoutMinCapacity) { + absl::Cord cord; + for (int i = 0; i < 2; ++i) { + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500); + buffer.SetLength(3); + memcpy(buffer.data(), i ? "def" : "Abc", 3); + cord.Append(std::move(buffer)); + } + absl::CordBuffer buffer = cord.GetAppendBuffer(1000, 900); + EXPECT_GE(buffer.capacity(), 1000); + EXPECT_EQ(buffer.length(), 0); + EXPECT_EQ(cord, "Abcdef"); +} + +TEST_P(CordTest, GetAppendBufferOnSubstring) { + // Create a large cord with a single flat and some extra capacity + absl::Cord cord; + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500); + buffer.SetLength(450); + memset(buffer.data(), 'x', 450); + cord.Append(std::move(buffer)); + cord.RemovePrefix(1); + + // Deny on substring + buffer = cord.GetAppendBuffer(6); + EXPECT_EQ(buffer.length(), 0); + EXPECT_EQ(cord, std::string(449, 'x')); +} + +TEST_P(CordTest, GetAppendBufferOnSharedCord) { + // Create a shared cord with a single flat and extra capacity + absl::Cord cord; + absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500); + buffer.SetLength(3); + memcpy(buffer.data(), "Abc", 3); + cord.Append(std::move(buffer)); + absl::Cord shared_cord = cord; + + // Deny on flat + buffer = cord.GetAppendBuffer(6); + EXPECT_EQ(buffer.length(), 0); + EXPECT_EQ(cord, "Abc"); + + buffer = absl::CordBuffer::CreateWithDefaultLimit(500); + buffer.SetLength(3); + memcpy(buffer.data(), "def", 3); + cord.Append(std::move(buffer)); + shared_cord = cord; + + // Deny on tree + buffer = cord.GetAppendBuffer(6); + EXPECT_EQ(buffer.length(), 0); + EXPECT_EQ(cord, "Abcdef"); +} + TEST_P(CordTest, TryFlatEmpty) { absl::Cord c; EXPECT_EQ(c.TryFlat(), ""); |