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// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_MEMORY_UNSAFE_SHARED_MEMORY_POOL_H_
#define BASE_MEMORY_UNSAFE_SHARED_MEMORY_POOL_H_
#include <memory>
#include <utility>
#include <vector>
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/memory/ref_counted.h"
#include "base/memory/unsafe_shared_memory_region.h"
#include "base/synchronization/lock.h"
#include "base/types/pass_key.h"
namespace base {
// UnsafeSharedMemoryPool manages allocation and pooling of
// UnsafeSharedMemoryRegions. Using pool saves cost of repeated shared memory
// allocations. Up-to 32 regions would be pooled. It is thread-safe. May return
// bigger regions than requested. If a requested size is increased, all stored
// regions are purged. Regions are returned to the buffer on destruction of
// |SharedMemoryHandle| if they are of a correct size.
class BASE_EXPORT UnsafeSharedMemoryPool
: public RefCountedThreadSafe<UnsafeSharedMemoryPool> {
public:
// Used to store the allocation result.
// This class returns memory to the pool upon destruction.
class BASE_EXPORT Handle {
public:
Handle(PassKey<UnsafeSharedMemoryPool>,
UnsafeSharedMemoryRegion region,
WritableSharedMemoryMapping mapping,
scoped_refptr<UnsafeSharedMemoryPool> pool);
~Handle();
// Disallow copy and assign.
Handle(const Handle&) = delete;
Handle& operator=(const Handle&) = delete;
const UnsafeSharedMemoryRegion& GetRegion() const LIFETIME_BOUND;
WritableSharedMemoryMapping& GetMapping() LIFETIME_BOUND {
return const_cast<WritableSharedMemoryMapping&>(
std::as_const(*this).GetMapping());
}
const WritableSharedMemoryMapping& GetMapping() const LIFETIME_BOUND;
private:
UnsafeSharedMemoryRegion region_;
WritableSharedMemoryMapping mapping_;
scoped_refptr<UnsafeSharedMemoryPool> pool_;
};
UnsafeSharedMemoryPool();
// Disallow copy and assign.
UnsafeSharedMemoryPool(const UnsafeSharedMemoryPool&) = delete;
UnsafeSharedMemoryPool& operator=(const UnsafeSharedMemoryPool&) = delete;
// Allocates a region of the given |size| or reuses a previous allocation if
// possible.
std::unique_ptr<Handle> MaybeAllocateBuffer(size_t size);
// Shuts down the pool, freeing all currently unused allocations and freeing
// outstanding ones as they are returned.
void Shutdown();
private:
friend class RefCountedThreadSafe<UnsafeSharedMemoryPool>;
~UnsafeSharedMemoryPool();
void ReleaseBuffer(UnsafeSharedMemoryRegion region,
WritableSharedMemoryMapping mapping);
Lock lock_;
// All shared memory regions cached internally are guaranteed to be
// at least `region_size_` bytes in size.
size_t region_size_ GUARDED_BY(lock_) = 0u;
// Cached unused regions and their mappings.
std::vector<std::pair<UnsafeSharedMemoryRegion, WritableSharedMemoryMapping>>
regions_ GUARDED_BY(lock_);
bool is_shutdown_ GUARDED_BY(lock_) = false;
};
} // namespace base
#endif // BASE_MEMORY_UNSAFE_SHARED_MEMORY_POOL_H_
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