QuicAlarms are now allocated out of an arena in QuicConnection

net/quic/quic_one_block_arena.h

Index: net/quic/quic_one_block_arena.h
diff --git a/net/quic/quic_one_block_arena.h b/net/quic/quic_one_block_arena.h
new file mode 100644
index 0000000000000000000000000000000000000000..b4d65e2fe8f9ecf95838ce929a412973d6d4cbd0
--- /dev/null
+++ b/net/quic/quic_one_block_arena.h
@@ -0,0 +1,81 @@
+// 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.
+  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 (!FLAGS_quic_enable_arena_allocation) {
+    return QuicArenaScopedPtr<T>(new T(std::forward<Args>(args)...));
+  }
+  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_