Built motion from commit 6a09e18b.|2.6.11

[motion2.git] / legacy-libs / grpc / deps / grpc / src / core / lib / gprpp / arena.h

diff --git a/legacy-libs/grpc/deps/grpc/src/core/lib/gprpp/arena.h b/legacy-libs/grpc/deps/grpc/src/core/lib/gprpp/arena.h
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+/*
+ *
+ * Copyright 2017 gRPC 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
+ *
+ *     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.
+ *
+ */
+
+// \file Arena based allocator
+// Allows very fast allocation of memory, but that memory cannot be freed until
+// the arena as a whole is freed
+// Tracks the total memory allocated against it, so that future arenas can
+// pre-allocate the right amount of memory
+
+#ifndef GRPC_CORE_LIB_GPRPP_ARENA_H
+#define GRPC_CORE_LIB_GPRPP_ARENA_H
+
+#include <grpc/support/port_platform.h>
+
+#include <new>
+#include <utility>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/sync.h>
+
+#include "src/core/lib/gpr/alloc.h"
+#include "src/core/lib/gpr/spinlock.h"
+#include "src/core/lib/gprpp/atomic.h"
+#include "src/core/lib/gprpp/pair.h"
+
+#include <stddef.h>
+
+namespace grpc_core {
+
+class Arena {
+ public:
+  // Create an arena, with \a initial_size bytes in the first allocated buffer.
+  static Arena* Create(size_t initial_size);
+
+  // Create an arena, with \a initial_size bytes in the first allocated buffer,
+  // and return both a void pointer to the returned arena and a void* with the
+  // first allocation.
+  static Pair<Arena*, void*> CreateWithAlloc(size_t initial_size,
+                                             size_t alloc_size);
+
+  // Destroy an arena, returning the total number of bytes allocated.
+  size_t Destroy();
+  // Allocate \a size bytes from the arena.
+  void* Alloc(size_t size) {
+    static constexpr size_t base_size =
+        GPR_ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(Arena));
+    size = GPR_ROUND_UP_TO_ALIGNMENT_SIZE(size);
+    size_t begin = total_used_.FetchAdd(size, MemoryOrder::RELAXED);
+    if (begin + size <= initial_zone_size_) {
+      return reinterpret_cast<char*>(this) + base_size + begin;
+    } else {
+      return AllocZone(size);
+    }
+  }
+
+  // TODO(roth): We currently assume that all callers need alignment of 16
+  // bytes, which may be wrong in some cases. When we have time, we should
+  // change this to instead use the alignment of the type being allocated by
+  // this method.
+  template <typename T, typename... Args>
+  T* New(Args&&... args) {
+    T* t = static_cast<T*>(Alloc(sizeof(T)));
+    new (t) T(std::forward<Args>(args)...);
+    return t;
+  }
+
+ private:
+  struct Zone {
+    Zone* prev;
+  };
+
+  // Initialize an arena.
+  // Parameters:
+  //   initial_size: The initial size of the whole arena in bytes. These bytes
+  //   are contained within 'zone 0'. If the arena user ends up requiring more
+  //   memory than the arena contains in zone 0, subsequent zones are allocated
+  //   on demand and maintained in a tail-linked list.
+  //
+  //   initial_alloc: Optionally, construct the arena as though a call to
+  //   Alloc() had already been made for initial_alloc bytes. This provides a
+  //   quick optimization (avoiding an atomic fetch-add) for the common case
+  //   where we wish to create an arena and then perform an immediate
+  //   allocation.
+  explicit Arena(size_t initial_size, size_t initial_alloc = 0)
+      : total_used_(initial_alloc), initial_zone_size_(initial_size) {}
+
+  ~Arena();
+
+  void* AllocZone(size_t size);
+
+  // Keep track of the total used size. We use this in our call sizing
+  // hysteresis.
+  Atomic<size_t> total_used_;
+  size_t initial_zone_size_;
+  gpr_spinlock arena_growth_spinlock_ = GPR_SPINLOCK_STATIC_INITIALIZER;
+  // If the initial arena allocation wasn't enough, we allocate additional zones
+  // in a reverse linked list. Each additional zone consists of (1) a pointer to
+  // the zone added before this zone (null if this is the first additional zone)
+  // and (2) the allocated memory. The arena itself maintains a pointer to the
+  // last zone; the zone list is reverse-walked during arena destruction only.
+  Zone* last_zone_ = nullptr;
+};
+
+}  // namespace grpc_core
+
+#endif /* GRPC_CORE_LIB_GPRPP_ARENA_H */