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A Custom Block Allocator for Speeding Up VC++ STL

, 30 Oct 2006 CPOL
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A block allocator for use with STL containers that greatly improves speed in programs doing massive data insertions and extractions.


block_allocator is a custom STL allocator for use with STL as implemented in Microsoft VC++. Rather than doing allocations on a per-node basis, block_allocator allocates memory in fixed sized chunks, and delivers portions of these chunks as requested. Typical speed improvements of 40% have been obtained with respect to the default allocator. The size of the chunks, set by the user, should not be too little (reduced speed improvements) nor too large (memory wasted). Experiment and see what sizes fit best to your application.

block_allocator can substitute for the default allocator in the following containers:

  • list,
  • set,
  • multiset,
  • map,
  • multimap,
and WON'T work with other containers such as vector or queue. Note however that vector and queue already perform allocation in chunks. The usage of block_allocator is fairly simple, for instance:
// block allocated list of ints with chunks of 1024 elements
std::list<int,block_allocator<int,1024> > l;
Normal containers and block allocated containers can coexist without problems.

Compatibility mode with MSVC++ 6.0/7.0

Due to limitations of the standard library provided with these compilers, the mode of usage explained above does not work here. To circumvent this problem one must proceed as follows: For each of the containers supported, there's an associated block allocated container derived from it thru use of block_allocator. You have to define an activating macro for each container to be defined prior to the inclusion of blockallocator.h:

  • list -> block_allocated_list (macro DEFINE_BLOCK_ALLOCATED_LIST),
  • set -> block_allocated_set (macro DEFINE_BLOCK_ALLOCATED_SET),
  • multiset -> block_allocated_multiset (macro DEFINE_BLOCK_ALLOCATED_MULTISET),
  • map -> block_allocated_map (macro DEFINE_BLOCK_ALLOCATED_MAP),
  • multimap -> block_allocated_multimap (macro DEFINE_BLOCK_ALLOCATED_MULTIMAP),

To use block allocation based STL in your application, define the corresponding activating macro, include blockallocator.h and then change your declarations as follows:

  • list<type> -> block_allocated_list<type,chunk_size>
  • set<key> -> block_allocated_set<key,chunk_size>
  • multiset<key> -> block_allocated_multiset<key,chunk_size>
  • map<key,type> -> block_allocated_map<key,type,chunk_size>
  • multimap<key,type> -> block_allocated_multimap<key,type,chunk_size>

where chunk_size is the size of the chunks. You can enter too the other optional template parameters (see MSVC++ STL docs for more info).

The MSVC++ 6.0/7.0 compatibility mode can also be used in MSVC++ 7.1, so you need not modify your block_allocator-related code when porting legacy code to 7.1.

Multithreading issues

Each block allocated container instance uses its own block_allocator, so no multithreading problems should arise as long as your program conveniently protects their containers for concurrent access (or if no two threads access the same container instance). This is the same scenario posed by regular STL classes (remember operations on containers are not guarded by CRITICAL_SECTIONs or anything similar), so the moral of it all is: If your program was multithread safe without block_allocator, it'll continue to be with it.

Version history

  • 29th Feb, 2000 - 1.1
    • Initial release in CodeProject.
  • 22nd Mar, 2001 - 1.2
    • Included definitions for operator== and operator!=. The lack of these caused linking errors when invoking list::swap() and similar methods. The funny thing about it is that no one ever reported this seemingly important bug, so either swap() is not that much used or not that many people use block_allocator!
  • 25th Oct, 2006 - 1.3
    • block_allocator now works with MSVC++ 7.1 and 8.0. Thanks to James May for helping with testing this new version of the code.
  • 30th Oct, 2006 - 1.4
    • Fixed some typedefs incorrectly made private in block_allocated_list, block_allocated_set, etc.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


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Comments and Discussions

Questioncould it work well with vc2008?? Pin
doityth77717-Sep-11 6:03
memberdoityth77717-Sep-11 6:03 
AnswerRe: could it work well with vc2008?? Pin
Joaquín M López Muñoz18-Sep-11 20:55
memberJoaquín M López Muñoz18-Sep-11 20:55 
QuestionIs it possible for a custom memory allocator to affect the Windows API MapViewOfFile? [modified] Pin
Member 80890191-Aug-11 2:51
memberMember 80890191-Aug-11 2:51 
AnswerRe: Is it possible for a custom memory allocator to affect the Windows API MapViewOfFile? Pin
Joaquín M López Muñoz1-Aug-11 19:48
memberJoaquín M López Muñoz1-Aug-11 19:48 
QuestionRe: Is it possible for a custom memory allocator to affect the Windows API MapViewOfFile? Pin
Member 80890194-Aug-11 20:31
memberMember 80890194-Aug-11 20:31 
Questionblock_allocated_list::sort() 2x slower than a standard stl::list()? Pin
Pet12326-May-08 20:33
memberPet12326-May-08 20:33 
AnswerRe: block_allocated_list::sort() 2x slower than a standard stl::list()? Pin
Joaquín M López Muñoz27-May-08 22:45
memberJoaquín M López Muñoz27-May-08 22:45 
GeneralLow Fragmentation Heap Pin
Paul Sanders (AlpineSoft)26-Oct-07 8:00
memberPaul Sanders (AlpineSoft)26-Oct-07 8:00 
GeneralFree Heap block 347970 modified at 348394 after it was freed Pin
Nyarlatotep19-Dec-06 7:33
memberNyarlatotep19-Dec-06 7:33 
I have used your block allocator with maps under a VC6 project inside two cdialogs (which are both childs of a Control bar and where i can switch from one to the other by a tab control)

in the first cdialog there are these definitions:

typedef block_allocated_map<long, long, 20> LONG2LONG;


in the other one:

typedef block_allocated_map<long, long, 20> LONG2LONG;


when the application is closed I receive the user breakpoint in the subject.

Commenting out the "LONG2LONG m_mapSrcAO;" definition in the first dialog solve the problem.
No one of the maps are modified (inserting or deleting entries). Only if I define the m_mapSrcAO member variable, I obtain the error.
GeneralRe: Free Heap block 347970 modified at 348394 after it was freed Pin
Nyarlatotep19-Dec-06 7:46
memberNyarlatotep19-Dec-06 7:46 

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