IPC pickling optimization for render passes.

base/pickle.h

 // Copyright (c) 2012 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 BASE_PICKLE_H__
 #define BASE_PICKLE_H__
 
 #include <string>
 
 #include "base/base_export.h"
@@ skipping 255 matching lines @@
   // with BeginWriteData), the Pickle can
   // be 'trimmed' if the amount of data required is less than originally
   // requested.  For example, you may have created a buffer with 10K of data,
   // but decided to only fill 10 bytes of that data.  Use this function
   // to trim the buffer so that we don't send 9990 bytes of unused data.
   // You cannot increase the size of the variable buffer; only shrink it.
   // This function assumes that the length of the variable buffer has
   // not been changed.
   void TrimWriteData(int length);
 
+  // Reserves space for upcoming writes when multiple writes will be made and
+  // their sizes are computed in advance. It can be significantly faster to call
+  // Reserve() before calling WriteFoo() multiple times.
+  void Reserve(size_t size);

[Tom Sepez, 2013/10/24 17:48:06]

Is |size| the additional amount of space to reserve, or the total space to
reserve?  I'd name the parameter |additional_capacity| or |new_capacity|
accordingly to match Resize() below.

[danakj, 2013/10/24 17:51:38]

Additional space, I will rename it to additional_capacity.

+
   // Payload follows after allocation of Header (header size is customizable).
   struct Header {
     uint32 payload_size;  // Specifies the size of the payload.
   };
 
   // Returns the header, cast to a user-specified type T.  The type T must be a
   // subclass of Header and its size must correspond to the header_size passed
   // to the Pickle constructor.
   template <class T>
   T* headerT() {
@@ skipping 35 matching lines @@
   // to pad out for the next write.
   char* BeginWrite(size_t length);
 
   // Completes the write operation by padding the data with NULL bytes until it
   // is padded. Should be paired with BeginWrite, but it does not necessarily
   // have to be called after the data is written.
   void EndWrite(char* dest, int length);
 
   // Resize the capacity, note that the input value should include the size of
   // the header: new_capacity = sizeof(Header) + desired_payload_capacity.
-  // A realloc() failure will cause a Resize failure... and caller should check
-  // the return result for true (i.e., successful resizing).
-  bool Resize(size_t new_capacity);
+  void Resize(size_t new_capacity);
 
   // Aligns 'i' by rounding it up to the next multiple of 'alignment'
   static size_t AlignInt(size_t i, int alignment) {
     return i + (alignment - (i % alignment)) % alignment;
   }
 
   // Find the end of the pickled data that starts at range_start.  Returns NULL
   // if the entire Pickle is not found in the given data range.
   static const char* FindNext(size_t header_size,
                               const char* range_start,
@@ skipping 10 matching lines @@
   // Allocation size of payload (or -1 if allocation is const).
   size_t capacity_;
   size_t variable_buffer_offset_;  // IF non-zero, then offset to a buffer.
 
   FRIEND_TEST_ALL_PREFIXES(PickleTest, Resize);
   FRIEND_TEST_ALL_PREFIXES(PickleTest, FindNext);
   FRIEND_TEST_ALL_PREFIXES(PickleTest, FindNextWithIncompleteHeader);
 };
 
 #endif  // BASE_PICKLE_H__