StackThreads/MP: version 0.77 User's Guide

Chapter 4: Memory Management

It may sound strange to talk about memory management in this manual. Yes, you can call any memory allocation function, including the standard malloc, from StackThreads/MP programs. However, once you start using StackThreads/MP in any serious parallel programs, you will soon notice that the system's default "malloc" function becomes a severe bottleneck. More specifically, typical malloc functions (including ones in Solaris libc) simply serialize all malloc calls using a mutex. If many threads contend, they cause many thread context switches of the underlying workers. In my experience, calling mallocs within a parallel section almost always makes a significant (negative) effect on performance. There are many xxx-malloc libraries, but most of them similarly serialize all malloc calls or are simply MT-unsafe (sure?).

We therefore provide some recommended alternatives to malloc. We also provide a mechanism with which you can easily replace the underlying memory allocator without changing application sources. With this mechanism, you can switch between several memory allocators (including the system's malloc). In this way, you will know how important are they for performance of parallel programs and what I am saying is not just a threat :-)

There are two (orthogonal) alternatives to the default malloc. One is to replace malloc with SGC library, and the other is a region-based allocator built on top of an underlying malloc. They are orthogonal. You can use either of them or combine both. We describe them in the following sections and then describe a mechanism with which you can easily switch between different memory-management alternatives.