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// Copyright (c) 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// An arena that consists of a single inlined block of |ArenaSize|. Useful to
// avoid repeated calls to malloc/new and to improve memory locality. DCHECK's
// if an allocation out of the arena ever fails in debug builds; falls back to
// heap allocation in release builds.
#ifndef NET_QUIC_QUIC_ONE_BLOCK_ARENA_H_
#define NET_QUIC_QUIC_ONE_BLOCK_ARENA_H_
#include "net/quic/quic_arena_scoped_ptr.h"
#include "net/quic/quic_flags.h"
#include "net/quic/quic_utils.h"
#define PREDICT_FALSE(x) x
namespace net {
template <uint32_t ArenaSize>
class QuicOneBlockArena {
static const uint32_t kMaxAlign = 8;
public:
QuicOneBlockArena();
// Instantiates an object of type |T| with |args|. |args| are perfectly
// forwarded to |T|'s constructor. The returned pointer's lifetime is
// controlled by QuicArenaScopedPtr.
template <typename T, typename... Args>
QuicArenaScopedPtr<T> New(Args&&... args);
private:
// Returns the size of |T| aligned up to |kMaxAlign|.
template <typename T>
static inline uint32_t AlignedSize() {
return ((sizeof(T) + (kMaxAlign - 1)) / kMaxAlign) * kMaxAlign;
}
// Actual storage.
// Subtle/annoying: the value '8' must be coded explicitly into the alignment
// declaration for MSVC.
QUIC_ALIGNED(8) char storage_[ArenaSize];
// Current offset into the storage.
uint32_t offset_;
DISALLOW_COPY_AND_ASSIGN(QuicOneBlockArena);
};
template <uint32_t ArenaSize>
QuicOneBlockArena<ArenaSize>::QuicOneBlockArena() : offset_(0) {}
template <uint32_t ArenaSize>
template <typename T, typename... Args>
QuicArenaScopedPtr<T> QuicOneBlockArena<ArenaSize>::New(Args&&... args) {
DCHECK_LT(AlignedSize<T>(), ArenaSize)
<< "Object is too large for the arena.";
static_assert(QUIC_ALIGN_OF(T) > 1,
"Objects added to the arena must be at least 2B aligned.");
if (PREDICT_FALSE(offset_ > ArenaSize - AlignedSize<T>())) {
LOG(DFATAL) << "Ran out of space in QuicOneBlockArena at " << this
<< ", max size was " << ArenaSize << ", failing request was "
<< AlignedSize<T>() << ", end of arena was " << offset_;
return QuicArenaScopedPtr<T>(new T(std::forward<Args>(args)...));
}
void* buf = &storage_[offset_];
new (buf) T(std::forward<Args>(args)...);
offset_ += AlignedSize<T>();
return QuicArenaScopedPtr<T>(buf,
QuicArenaScopedPtr<T>::ConstructFrom::kArena);
}
} // namespace net
#endif // NET_QUIC_QUIC_ONE_BLOCK_ARENA_H_