Boehm garbage collector

Hans Boehm describes the operation of the collector as follows:

{{Quotation|The collector uses a mark-sweep algorithm. It provides incremental and generational collection under operating systems which provide the right kind of virtual memory support. (Currently this includes SunOS[45], IRIX, OSF/1, Linux, and Windows, with varying restrictions.) It allows finalization code to be invoked when an object is collected. It can take advantage of type information to locate pointers if such information is provided, but it is usually used without such information.|http://www.hboehm.info/gc/#details}}

Boehm GC can also run in leak detection mode[http://www.hboehm.info/gc/leak.html Using the Garbage Collector as Leak Detector] 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++ (trees of constant small arrays), 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 {{tt|malloc()}} with {{tt|GC_MALLOC()}} calls, replacing {{tt|realloc()}} with {{tt|GC_REALLOC()}} calls, and removing {{tt|free()}} calls. The code piece below shows how one can use Boehm instead of traditional malloc and free in C.[http://www.hboehm.info/gc/simple_example.html Using the Garbage Collector: A simple example]

1. include
2. include
3. include

int main(void)

{

int i;

const int size = 10000000;

GC_INIT();

for (i = 0; i < size; ++i)

{

int **p = GC_MALLOC(sizeof *p);

int *q = GC_MALLOC_ATOMIC(sizeof *q);

assert(*p == 0);

*p = GC_REALLOC(q, 2 * sizeof *p);

if (i == size-1)

printf("Heap size = %zu\n", GC_get_heap_size());

}

return 0;

}

For completeness, Boehm supports explicit deallocation via {{tt|GC_FREE()}}.{{cite web |title=Garbage Collector Interface |url=https://www.hboehm.info/gc/gcinterface.html |website=www.hboehm.info}} All the substitution can be done using preprocessor macros.

The Boehm GC is used by many projects[https://github.com/ivmai/bdwgc/wiki/Known-clients Known BDWGC uses] that are implemented in C or C++ like Inkscape, as well as by runtime environments for a number of other languages, including Crystal, the Codon high performance python compiler,{{cite web | url=https://github.com/exaloop/codon | title=Exaloop/Codon | website=GitHub }} 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), GNUstep optionally, and libgc-d[https://github.com/lycus/libgc-d 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 macOS) and Microsoft Windows, and provides a number of advanced features including incremental collection, parallel collection and a variety of finalizer semantics.

{{Reflist|refs=

{{Citation

| last1 = Koranne

| first1 = Sandeep

| title = Handbook of Open Source Tools

| publisher = Springer

| pages = 151–154

| year = 2011

| bibcode = 2011hoos.book.....K

| isbn = 978-1441977199

| url = https://books.google.com/books?id=ukXrNh2g6fQC&pg=PA151

| postscript= .

}}

}}

{{Portal|Free and open-source software}}

• {{Official website}}
• {{SourceForge|bdwgc}}
• {{GitHub|ivmai/bdwgc/|Git repo for BoehmGC development}}
• [http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2310.pdf Transparent Programmer-Directed Garbage Collection for C++, Hans-J. Boehm and Michael Spertus]
• [http://www.drdobbs.com/the-boehm-collector-for-c-and-c/184401632 Dr. Dobbs The Boehm Collector for C and C++, Gene Michael Stover, March 01, 2003]

{{Memory management}}

Category:Automatic memory management

Category:C++ libraries

Category:C (programming language) libraries

Category:Memory management software