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Boehm garbage collector

Boehm–Demers–Weiser Garbage Collector
Written in C and C++
Type garbage collector
License similar to X11 (free software)

In computer science, the Boehm–Demers–Weiser garbage collector, often simply known as Boehm GC, is a conservative garbage collector for C and C++.[1]

Boehm GC is free software distributed under a permissive free software licence similar to the X11 license.


  • Design 1
  • Operation 2
  • Uses and ports 3
  • References 4
  • External links 5


The developer describes the operation of the collector as follows:

Boehm GC can also run in leak detection mode[2] in which memory management is still done manually, but the Boehm GC can check if it is done properly. In this way a programmer can find memory leaks and double deallocations.

Boehm GC is also distributed with a C string handling library called cords. This is similar to ropes in C++ (strings are trees of small arrays, and they never change), but instead of using reference counting for proper deallocation, it relies on garbage collection to free objects. Cords are good at handling very large texts, modifications to them in the middle, slicing, concatenating, and keeping history of changes (undo/redo functionality).


The garbage collector works with most unmodified C programs, simply by replacing malloc() with GC_MALLOC() calls, replacing realloc() with GC_REALLOC() calls, and removing free() calls.[1] The code piece below shows how one can use Boehm instead of traditional malloc and free in C.[3]


int main(void)
    int i;

    for (i = 0; i < 10000000; ++i)
        int **p = (int**)GC_MALLOC(sizeof(int *));
        int *q = (int*)GC_MALLOC_ATOMIC(sizeof(int));

        assert(*p == 0);
        *p = (int*)GC_REALLOC(q, 2 * sizeof(int));
        if (i % 100000 == 0)
            printf("Heap size = %zu\n", GC_get_heap_size());

    return 0;

Uses and ports

The Boehm GC is used by many projects that are implemented in C or C++ like Inkscape, as well as by runtime environments for a number of other languages, including the GNU Compiler for Java runtime environment, the Portable.NET project, Embeddable Common Lisp, GNU Guile, the Mono implementation of the Microsoft .NET platform (also using precise compacting GC since version 2.8), and libgc-d (a binding to libgc for the D programming language, used primarily in the MCI). It supports numerous operating systems, including many Unix variants (such as Mac OS X) and Microsoft Windows, and provides a number of advanced features including incremental collection, parallel collection and a variety of finalizer semantics.


  1. ^ a b Koranne, Sandeep (2011), Handbook of Open Source Tools, Springer, pp. 151–154,  
  2. ^ Using the Garbage Collector as Leak Detector
  3. ^ Using the Garbage Collector: A simple example

External links

  • Homepage
  • Boehm garbage collector on
  • Git repo for BoehmGC development
  • Transparent Programmer-Directed Garbage Collection for C++, Hans-J. Boehm and Michael Spertus
  • Using the C/C++ Garbage Collection Library
  • Dr. Dobbs The Boehm Collector for C and C++, Gene Michael Stover, March 01, 2003
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