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Learn more about: How to: Use Alloc and Free to Improve Memory Performance |
How to: Use Alloc and Free to Improve Memory Performance |
11/04/2016 |
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e1fab9e8-a97d-4104-bead-e95958db79f9 |
This document shows how to use the concurrency::Alloc and concurrency::Free functions to improve memory performance. It compares the time that is required to reverse the elements of an array in parallel for three different types that each specify the new and delete operators.
The Alloc and Free functions are most useful when multiple threads frequently call both Alloc and Free. The runtime holds a separate memory cache for each thread; therefore, the runtime manages memory without the use of locks or memory barriers.
The following example shows three types that each specify the new and delete operators. The new_delete class uses the global new and delete operators, the malloc_free class uses the C Runtime malloc and free functions, and the Alloc_Free class uses the Concurrency Runtime Alloc and Free functions.
[!code-cppconcrt-allocators#1]
The following example shows the swap and reverse_array functions. The swap function exchanges the contents of the array at the specified indices. It allocates memory from the heap for the temporary variable. The reverse_array function creates a large array and computes the time that is required to reverse that array several times in parallel.
[!code-cppconcrt-allocators#2]
The following example shows the wmain function, which computes the time that is required for the reverse_array function to act on the new_delete, malloc_free, and Alloc_Free types, each of which uses a different memory allocation scheme.
[!code-cppconcrt-allocators#3]
The complete example follows.
[!code-cppconcrt-allocators#4]
This example produces the following sample output for a computer that has four processors.
Took 2031 ms with new/delete.
Took 1672 ms with malloc/free.
Took 656 ms with Alloc/Free.
In this example, the type that uses the Alloc and Free functions provides the best memory performance because the Alloc and Free functions are optimized for frequently allocating and freeing blocks of memory from multiple threads.
Copy the example code and paste it in a Visual Studio project, or paste it in a file that is named allocators.cpp and then run the following command in a Visual Studio Command Prompt window.
cl.exe /EHsc allocators.cpp