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// Copyright 2015 The Gemmlowp 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.
// allocator.h: a buffer allocator that allows avoiding most of the
// malloc/free overhead, by:
// 1. Requiring all N allocations to be reserved in advance, and
// then commited at once, turning N allocations into 1.
// 2. Being persistent, the allocated storage is reused across commits,
// and only reallocated as needed when the commit size gets larger.
//
// This is driven by Android-specific needs:
// 1. On Android, the default (Bionic) allocator tends to aggressively
// unmap pages, which means that malloc/free can be surprisingly expensive.
// 2. On Android, stack allocations with alloca() can't be as large as on
// desktop platforms.
//
// General usage:
// 1. Reserve blocks by calling Reserve(), which returns a Handle.
// 2. Call Commit() once.
// 3. Now it is possible to get pointers to allocated buffers by calling
// GetPointer().
// 4. Call Decommit() once.
// 5. The allocator is now reverted to its original state, except that
// it retained its allocated storage, so the next Commit() will be faster.
// The allocated storage is only freed when the Allocator object is
// destroyed.
#ifndef GEMMLOWP_INTERNAL_ALLOCATOR_H_
#define GEMMLOWP_INTERNAL_ALLOCATOR_H_
#include "common.h"
namespace gemmlowp {
enum class TypeId : std::uint8_t { Uint8, Int8, Uint16, Int16, Uint32, Int32 };
template <typename T>
struct GetTypeIdImpl {};
template <typename T>
inline TypeId GetTypeId() {
return GetTypeIdImpl<T>::Value;
}
template <typename T>
struct GetTypeIdImpl<const T> : GetTypeIdImpl<T> {};
#define GEMMLOWP_REGISTER_TYPEID(type_, id) \
template <> \
struct GetTypeIdImpl<type_> { \
static const TypeId Value = TypeId::id; \
};
GEMMLOWP_REGISTER_TYPEID(std::uint8_t, Uint8)
GEMMLOWP_REGISTER_TYPEID(std::int8_t, Int8)
GEMMLOWP_REGISTER_TYPEID(std::uint16_t, Uint16)
GEMMLOWP_REGISTER_TYPEID(std::int16_t, Int16)
GEMMLOWP_REGISTER_TYPEID(std::uint32_t, Uint32)
GEMMLOWP_REGISTER_TYPEID(std::int32_t, Int32)
class Allocator {
public:
Allocator()
: committed_(false),
storage_size_(0),
storage_(nullptr),
reserved_blocks_(0),
reserved_bytes_(0),
generation_(0) {}
~Allocator() {
assert(!committed_);
assert(!reserved_blocks_);
DeallocateStorage();
}
// Alignment of allocated blocks.
static constexpr std::size_t kAlignment = kDefaultCacheLineSize;
// This is all we need so far, and since the usage pattern is fixed,
// there is no point in allowing more until we need to.
static constexpr std::size_t kMaxBlocks = 5;
void Commit() {
assert(!committed_);
if (reserved_bytes_ > storage_size_) {
DeallocateStorage();
storage_size_ = RoundUpToPowerOfTwo(reserved_bytes_);
storage_ = aligned_alloc(kAlignment, storage_size_);
}
ReleaseBuildAssertion(!storage_size_ || storage_, "allocation failure");
committed_ = true;
}
void Decommit() {
assert(committed_);
committed_ = false;
generation_++;
reserved_blocks_ = 0;
reserved_bytes_ = 0;
}
// See generation_
typedef std::size_t generation_t;
// A handle on a reserved block. The user obtains
// one by calling Reserve() and, after committing,
// passes it to GetPointer().
class Handle {
std::uint8_t index_;
generation_t generation_;
TypeId type_;
friend class Allocator;
};
// Reserves a block sized for n elements of type T, and
// returns a handle to it. Must be called before committing.
template <typename T>
Handle Reserve(std::size_t n) {
assert(!committed_ && "can't reserve blocks while committed");
assert(reserved_blocks_ < kMaxBlocks &&
"didn't expect to allocate this many blocks");
const std::size_t bytes = RoundUp<kAlignment>(n * sizeof(T));
const std::size_t offset = reserved_bytes_;
const std::size_t index = reserved_blocks_;
reserved_blocks_offsets_[index] = offset;
Handle h;
h.index_ = index;
h.generation_ = generation_;
h.type_ = GetTypeId<T>();
reserved_blocks_++;
reserved_bytes_ += bytes;
return h;
}
// Returns the pointer to the allocated buffer for the given handle.
// Must be called after committing.
template <typename T>
T* GetPointer(const Handle& h) const {
assert(committed_ && "can't get block pointers unless committed");
assert(h.index_ < reserved_blocks_ &&
"bad handle, points to inexistant block");
assert(h.generation_ == generation_ &&
"handle from earlier generation, have decommitted since");
assert(h.type_ == GetTypeId<T>() && "type mismatch");
std::size_t offset = reserved_blocks_offsets_[h.index_];
std::uintptr_t addr = reinterpret_cast<std::uintptr_t>(storage_) + offset;
return reinterpret_cast<T*>(addr);
}
private:
void DeallocateStorage() {
assert(!committed_);
aligned_free(storage_);
storage_size_ = 0;
}
// Set to true by Commit() and to false by Decommit(). Initially false.
bool committed_;
// The actually allocated storage size and buffer pointer.
std::size_t storage_size_;
mutable void* storage_;
// The number of blocks that have been reserved by Reserve().
std::size_t reserved_blocks_;
// The number of bytes that have been reserved by Reserve().
std::size_t reserved_bytes_;
// The offsets of reserved blocks into the storage buffer.
std::size_t reserved_blocks_offsets_[kMaxBlocks];
// The 'generation' is incremented on Decommit() and allows catching
// bad GetPointer() calls still referring to a previous commit.
generation_t generation_;
};
} // namespace gemmlowp
#endif // GEMMLOWP_INTERNAL_ALLOCATOR_H_
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