src: add allocation utils to env

Add a RAII utility for managing blocks of memory that have been allocated with the `ArrayBuffer::Allocator` for a given `Isolate`.
nodejs · addaleax · Feb 19, 2019 · Feb 18, 2019 · Feb 19, 2019 · Feb 18, 2019
commit 41e81b1d063ba8fbe446701a96c839cfb122d0e1
diff --git a/src/env-inl.h b/src/env-inl.h
@@ -715,6 +715,105 @@ inline IsolateData* Environment::isolate_data() const {
   return isolate_data_;
 }
 
+inline char* Environment::AllocateUnchecked(size_t size) {
+  return static_cast<char*>(
+      isolate_data()->allocator()->AllocateUninitialized(size));
+}
+
+inline char* Environment::Allocate(size_t size) {
+  char* ret = AllocateUnchecked(size);
+  CHECK_NE(ret, nullptr);
+  return ret;
+}
+
+inline void Environment::Free(char* data, size_t size) {
+  if (data != nullptr)
+    isolate_data()->allocator()->Free(data, size);
+}
+
+inline AllocatedBuffer Environment::AllocateManaged(size_t size, bool checked) {
+  char* data = checked ? Allocate(size) : AllocateUnchecked(size);
+  if (data == nullptr) size = 0;
+  return AllocatedBuffer(this, uv_buf_init(data, size));
+}
+
+inline AllocatedBuffer::AllocatedBuffer(Environment* env, uv_buf_t buf)
+    : env_(env), buffer_(buf) {}
+
+inline void AllocatedBuffer::Resize(size_t len) {
+  char* new_data = env_->Reallocate(buffer_.base, buffer_.len, len);
+  CHECK_IMPLIES(len > 0, new_data != nullptr);
+  buffer_.base = new_data;
+  buffer_.len = len;
+}
+
+inline uv_buf_t AllocatedBuffer::release() {
+  uv_buf_t ret = buffer_;
+  buffer_ = uv_buf_init(nullptr, 0);
+  return ret;
+}
+
+inline char* AllocatedBuffer::data() {
+  return buffer_.base;
+}
+
+inline const char* AllocatedBuffer::data() const {
+  return buffer_.base;
+}
+
+inline size_t AllocatedBuffer::size() const {
+  return buffer_.len;
+}
+
+inline AllocatedBuffer::AllocatedBuffer(Environment* env)
+    : env_(env), buffer_(uv_buf_init(nullptr, 0)) {}
+
+inline AllocatedBuffer::AllocatedBuffer(AllocatedBuffer&& other)
+    : AllocatedBuffer() {
+  *this = std::move(other);
+}
+
+inline AllocatedBuffer& AllocatedBuffer::operator=(AllocatedBuffer&& other) {
+  clear();
+  env_ = other.env_;
+  buffer_ = other.release();
+  return *this;
+}
+
+inline AllocatedBuffer::~AllocatedBuffer() {
+  clear();
+}
+
+inline void AllocatedBuffer::clear() {
+  uv_buf_t buf = release();
+  env_->Free(buf.base, buf.len);
+}
+
+// It's a bit awkward to define this Buffer::New() overload here, but it
+// avoids a circular dependency with node_internals.h.
+namespace Buffer {
+v8::MaybeLocal<v8::Object> New(Environment* env,
+                               char* data,
+                               size_t length,
+                               bool uses_malloc);
+}
+
+inline v8::MaybeLocal<v8::Object> AllocatedBuffer::ToBuffer() {
+  CHECK_NOT_NULL(env_);
+  v8::MaybeLocal<v8::Object> obj = Buffer::New(env_, data(), size(), false);
+  if (!obj.IsEmpty()) release();
+  return obj;
+}
+
+inline v8::Local<v8::ArrayBuffer> AllocatedBuffer::ToArrayBuffer() {
+  CHECK_NOT_NULL(env_);
+  uv_buf_t buf = release();
+  return v8::ArrayBuffer::New(env_->isolate(),
+                              buf.base,
+                              buf.len,
+                              v8::ArrayBufferCreationMode::kInternalized);
+}
+
 inline void Environment::ThrowError(const char* errmsg) {
   ThrowError(v8::Exception::Error, errmsg);
 }

diff --git a/src/env.cc b/src/env.cc
@@ -22,6 +22,7 @@ namespace node {
 
 using errors::TryCatchScope;
 using v8::Boolean;
+using v8::ArrayBuffer;
 using v8::Context;
 using v8::EmbedderGraph;
 using v8::External;
@@ -905,6 +906,23 @@ void Environment::BuildEmbedderGraph(Isolate* isolate,
   });
 }
 
+char* Environment::Reallocate(char* data, size_t old_size, size_t size) {
+  // If we know that the allocator is our ArrayBufferAllocator, we can let
+  // if reallocate directly.
+  if (isolate_data()->uses_node_allocator()) {
+    return static_cast<char*>(
+        isolate_data()->node_allocator()->Reallocate(data, old_size, size));
+  }
+  // Generic allocators do not provide a reallocation method; we need to
+  // allocate a new chunk of memory and copy the data over.
+  char* new_data = AllocateUnchecked(size);
+  if (new_data == nullptr) return nullptr;
+  memcpy(new_data, data, std::min(size, old_size));
+  if (size > old_size)
+    memset(new_data + old_size, 0, size - old_size);
+  Free(data, old_size);
+  return new_data;
+}
 
 // Not really any better place than env.cc at this moment.
 void BaseObject::DeleteMe(void* data) {

diff --git a/src/env.h b/src/env.h
@@ -476,6 +476,36 @@ enum class DebugCategory {
   CATEGORY_COUNT
 };
 
+// A unique-pointer-ish object that is compatible with the JS engine's
+// ArrayBuffer::Allocator.
+struct AllocatedBuffer {
+ public:
+  explicit inline AllocatedBuffer(Environment* env = nullptr);
+  inline AllocatedBuffer(Environment* env, uv_buf_t buf);
+  inline ~AllocatedBuffer();
+  inline void Resize(size_t len);
+
+  inline uv_buf_t release();
+  inline char* data();
+  inline const char* data() const;
+  inline size_t size() const;
+  inline void clear();
+
+  inline v8::MaybeLocal<v8::Object> ToBuffer();
+  inline v8::Local<v8::ArrayBuffer> ToArrayBuffer();
+
+  inline AllocatedBuffer(AllocatedBuffer&& other);
+  inline AllocatedBuffer& operator=(AllocatedBuffer&& other);
+  AllocatedBuffer(const AllocatedBuffer& other) = delete;
+  AllocatedBuffer& operator=(const AllocatedBuffer& other) = delete;
+
+ private:
+  Environment* env_;
+  uv_buf_t buffer_;
+
+  friend class Environment;
+};
+
 class Environment {
  public:
   class AsyncHooks {
@@ -697,6 +727,15 @@ class Environment {
 
   inline IsolateData* isolate_data() const;
 
+  // Utilites that allocate memory using the Isolate's ArrayBuffer::Allocator.
+  // In particular, using AllocateManaged() will provide a RAII-style object
+  // with easy conversion to `Buffer` and `ArrayBuffer` objects.
+  inline AllocatedBuffer AllocateManaged(size_t size, bool checked = true);
+  inline char* Allocate(size_t size);
+  inline char* AllocateUnchecked(size_t size);
+  char* Reallocate(char* data, size_t old_size, size_t size);
+  inline void Free(char* data, size_t size);
+
   inline bool printed_error() const;
   inline void set_printed_error(bool value);