C++ bindings

mojo/public/bindings/lib/buffer.h

+// Copyright 2013 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.
+
+#ifndef MOJO_PUBLIC_BINDINGS_LIB_BUFFER_H_
+#define MOJO_PUBLIC_BINDINGS_LIB_BUFFER_H_
+
+#include <stdint.h>
+
+#include "mojo/public/system/macros.h"
+
+namespace mojo {
+
+class Buffer {
+ public:
+  virtual ~Buffer() {}
+  virtual void* Allocate(uint32_t num_bytes) = 0;
+};
+
+// The following class is designed to be allocated on the stack.  If necessary,
+// it will failover to allocating objects on the heap.
+class StackBuffer : public Buffer {
+ public:
+  StackBuffer();
+  virtual ~StackBuffer();
+
+  virtual void* Allocate(uint32_t num_bytes) MOJO_OVERRIDE;
+
+ private:
+  static const uint32_t kMinSegmentSize = 512;
+
+  struct Segment {
+    Segment* next;
+    char* cursor;
+    char* end;
+  };
+
+  void* AllocateInSegment(Segment* segment, uint32_t num_bytes);
+  void AddOverflowSegment(uint32_t delta);
+
+  char fixed_data_[kMinSegmentSize];
+  Segment fixed_;
+  Segment* overflow_;
+
+  // Not implemented.
+  StackBuffer(const StackBuffer&);
+  void operator=(const StackBuffer&);
+};
+
+// ContiguousBuffer provides a simple way to allocate objects within a
+// contiguous chunk of memory. Objects are allocated by calling the |Allocate|
+// method, which extends the buffer accordingly. Objects allocated in this way
+// are not freed explicitly. Instead, they remain valid so long as the
+// ContiguousBuffer remains valid.  The Leak method may be used to steal the
+// underlying memory from the ContiguousBuffer.
+//
+// Typical usage:
+//
+//   {
+//     ContiguousBuffer buf;
+//
+//     int* a = static_cast<int*>(buf.Allocate(sizeof(int)));
+//     *a = 2;
+//
+//     double* b = static_cast<double*>(buf.Grow(sizeof(double)));
+//     *b = 3.14f;
+//
+//     void* data = buf.Leak();
+//     Process(data);
+//
+//     free(data);
+//   }
+//
+class ContiguousBuffer : public Buffer {
+ public:
+  ContiguousBuffer();
+  virtual ~ContiguousBuffer();
+
+  // Grows the buffer by |num_bytes| and returns a pointer to the start of the
+  // addition. The resulting address is 8-byte aligned, and the contents of the
+  // memory is zero-filled.
+  virtual void* Allocate(uint32_t num_bytes) MOJO_OVERRIDE;
+
+  uint32_t size() const { return size_; }
+
+  // Returns the internal memory owned by the Buffer to the caller. The Buffer
+  // relinquishes its pointer, effectively resetting the state of the Buffer
+  // and leaving the caller responsible for freeing the returned memory address
+  // when no longer needed.
+  void* Leak();
+
+ private:
+  char* ptr_;
+  uint32_t size_;
+  uint32_t capacity_;
+
+  // Not implemented.
+  ContiguousBuffer(const ContiguousBuffer&);
+  void operator=(const ContiguousBuffer&);
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_BINDINGS_LIB_BUFFER_H_