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// Copyright 2019 The TCMalloc 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.
#ifndef TCMALLOC_PAGE_HEAP_ALLOCATOR_H_
#define TCMALLOC_PAGE_HEAP_ALLOCATOR_H_
#include <stddef.h>
#include "absl/base/attributes.h"
#include "absl/base/optimization.h"
#include "absl/base/thread_annotations.h"
#include "tcmalloc/arena.h"
#include "tcmalloc/common.h"
#include "tcmalloc/internal/logging.h"
GOOGLE_MALLOC_SECTION_BEGIN
namespace tcmalloc {
namespace tcmalloc_internal {
struct AllocatorStats {
// Number of allocated but unfreed objects
size_t in_use;
// Number of objects created (both free and allocated)
size_t total;
};
// Simple allocator for objects of a specified type. External locking
// is required before accessing one of these objects.
template <class T>
class PageHeapAllocator {
public:
constexpr PageHeapAllocator()
: arena_(nullptr), free_list_(nullptr), stats_{0, 0} {}
// We use an explicit Init function because these variables are statically
// allocated and their constructors might not have run by the time some
// other static variable tries to allocate memory.
void Init(Arena* arena) ABSL_EXCLUSIVE_LOCKS_REQUIRED(pageheap_lock) {
arena_ = arena;
// Reserve some space at the beginning to avoid fragmentation.
Delete(New());
}
ABSL_ATTRIBUTE_RETURNS_NONNULL T* New()
ABSL_EXCLUSIVE_LOCKS_REQUIRED(pageheap_lock) {
// Consult free list
T* result = free_list_;
stats_.in_use++;
if (ABSL_PREDICT_FALSE(result == nullptr)) {
stats_.total++;
return reinterpret_cast<T*>(arena_->Alloc(sizeof(T)));
}
free_list_ = *(reinterpret_cast<T**>(free_list_));
return result;
}
void Delete(T* p) ABSL_ATTRIBUTE_NONNULL()
ABSL_EXCLUSIVE_LOCKS_REQUIRED(pageheap_lock) {
*(reinterpret_cast<void**>(p)) = free_list_;
free_list_ = p;
stats_.in_use--;
}
AllocatorStats stats() const ABSL_EXCLUSIVE_LOCKS_REQUIRED(pageheap_lock) {
return stats_;
}
private:
// Arena from which to allocate memory
Arena* arena_;
// Free list of already carved objects
T* free_list_ ABSL_GUARDED_BY(pageheap_lock);
AllocatorStats stats_ ABSL_GUARDED_BY(pageheap_lock);
};
} // namespace tcmalloc_internal
} // namespace tcmalloc
GOOGLE_MALLOC_SECTION_END
#endif // TCMALLOC_PAGE_HEAP_ALLOCATOR_H_
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