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 <stddef.h>
+
+#include "mojo/public/system/macros.h"
+
+namespace mojo {
+
+// Allocations are 8-byte aligned and zero-filled.
+class Buffer {
+ public:
+  virtual ~Buffer() {}
+  virtual void* Allocate(size_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 ScratchBuffer : public Buffer {
+ public:
+  ScratchBuffer();
+  virtual ~ScratchBuffer();
+
+  virtual void* Allocate(size_t num_bytes) MOJO_OVERRIDE;
+
+ private:
+  enum { kMinSegmentSize = 512 };
+
+  struct Segment {
+    Segment* next;
+    char* cursor;
+    char* end;
+  };
+
+  void* AllocateInSegment(Segment* segment, size_t num_bytes);
+  void AddOverflowSegment(size_t delta);
+
+  char fixed_data_[kMinSegmentSize];
+  Segment fixed_;
+  Segment* overflow_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(ScratchBuffer);
+};
+
+// FixedBuffer provides a simple way to allocate objects within a fixed 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 FixedBuffer remains
+// valid.  The Leak method may be used to steal the underlying memory from the
+// FixedBuffer.
+//
+// Typical usage:
+//
+//   {
+//     FixedBuffer buf(8 + 8);
+//
+//     int* a = static_cast<int*>(buf->Allocate(sizeof(int)));
+//     *a = 2;
+//
+//     double* b = static_cast<double*>(buf->Allocate(sizeof(double)));
+//     *b = 3.14f;
+//
+//     void* data = buf.Leak();
+//     Process(data);
+//
+//     free(data);
+//   }
+//
+class FixedBuffer : public Buffer {
+ public:
+  explicit FixedBuffer(size_t size);
+  virtual ~FixedBuffer();
+
+  // 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(size_t num_bytes) MOJO_OVERRIDE;
+
+  size_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_;
+  size_t cursor_;
+  size_t size_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(FixedBuffer);
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_BINDINGS_LIB_BUFFER_H_