Add a memory arena for the audio pipeline

1 files changed, 85 insertions, 0 deletions

diff --git a/src/memory/include/arena.hpp b/src/memory/include/arena.hpp
new file mode 100644
index 00000000..26d49d27
--- /dev/null
+++ b/src/memory/include/arena.hpp
@@ -0,0 +1,85 @@
+#pragma once
+
+#include <cstdint>
+#include <optional>
+#include <utility>
+
+#include "freertos/FreeRTOS.h"
+#include "freertos/queue.h"
+#include "span.hpp"
+#include "sys/_stdint.h"
+
+namespace memory {
+
+class Arena;
+
+/*
+ * A pointer to data that has been given out by an Arena, plus extra accounting
+ * information so that it can be returned properly.
+ */
+struct ArenaPtr {
+  Arena* owner;
+  std::byte* start;
+  std::size_t size;
+  // A convenience for keeping track of the subset of the block that has had
+  // data placed within it.
+  std::size_t used_size;
+};
+
+/*
+ * A basic memory arena. This class mediates access to fixed-size blocks of
+ * memory within a larger contiguous block. This is faster than re-allocating
+ * smaller blocks every time they're needed, and lets us easily limit the
+ * maximum size of the memory used.
+ *
+ * A single arena instance is safe to be used concurrently by multiple tasks,
+ * however there is no built in synchronisation of the underlying memory.
+ */
+class Arena {
+ public:
+  Arena(std::size_t block_size, std::size_t num_blocks, uint32_t alloc_flags);
+  ~Arena();
+
+  /*
+   * Attempts to receive an allocation from this arena. Returns absent if
+   * there are no blocks left.
+   */
+  auto Acquire() -> std::optional<ArenaPtr>;
+
+  /* Returns a previously allocated block to this arena. */
+  auto Return(ArenaPtr) -> void;
+
+  /* Returns the number of blocks that are currently free. */
+  auto BlocksFree() -> std::size_t;
+
+  Arena(const Arena&) = delete;
+  Arena& operator=(const Arena&) = delete;
+
+ private:
+  std::size_t block_size_;
+  // The large memory allocation that is divided into blocks.
+  std::byte* pool_;
+  // A FreeRTOS queue containing the blocks that are currently unused.
+  QueueHandle_t free_blocks_;
+};
+
+/*
+ * Wrapper around an ArenaPtr that handles acquiring and returning the block
+ * through RAII.
+ */
+class ArenaRef {
+ public:
+  static auto Acquire(Arena* a) -> std::optional<ArenaRef>;
+  explicit ArenaRef(ArenaPtr ptr);
+  ~ArenaRef();
+
+  auto Release() -> ArenaPtr;
+
+  ArenaRef(ArenaRef&&);
+  ArenaRef(const ArenaRef&) = delete;
+  Arena& operator=(const Arena&) = delete;
+
+  ArenaPtr ptr;
+};
+
+}  // namespace memory