rzbdz / min-cgc

A simple and slow conservative garbage collector using mark and sweep with explicit linked list malloc implementation for C programing language. (for leaning garbage collection purpose). Could be modified to adapt xv6.

min-cgc

A simple and NOT-fast conservative garbage collector (merely a toy for learning basic garbage collection concepts) using mark-and-sweep for C programing language. Provide interface of malloc/free and garbage collection without side effect.

The cgc_malloc, cgc_free, cgc_realloc package is tested using CSAPP3e malloclab mdriver to test. The gc package is tested using some novice codes in the cgc.c source file.

algorithm:

• cgc_malloc() basically use ordinary segregated explicit free lists to manage heap memory allocated by calling sbrk() (might be switched to mmap() in the future).

• the gc algorithm is simple mark-and-sweep (STW), if possible, could be implemented in incremental way.

interfaces:

• int cgc_init() explicitly delegate memory management to min-cgc.

• int cgc(void) stop the world and do gc.

• void* cgc_malloc(size_t size) similar to malloc() in unix.

• void cgc_free(void *ptr) similar to free() in unix.

• void *realloc(void *ptr, size_t size)

performance

• The cgc_malloc, cgc_free, cgc_realloc test results using CSAPP3e mdriver in malloclab:

  trace	valid	util	ops	secs	Kops
  0	yes	98%	5694	0.000721	7902
  1	yes	94%	5848	0.000940	6221
  2	yes	96%	6648	0.001482	4486
  3	yes	95%	5380	0.001758	3060
  4	yes	94%	14400	0.000429	33535
  5	yes	94%	4800	0.000927	5180
  6	yes	93%	4800	0.000799	6008
  7	yes	94%	12000	0.001891	6348
  8	yes	81%	24000	0.002075	11567
  9	yes	99%	14401	0.000365	39433
  10	yes	99%	14401	0.000211	68348
  Total	pass	94%	112372	0.011597	9690

• The garbage collection performance:. (none, it's very slow)
• test cgc calls with gc most the time and free in test_many_objects(@see src code):

  throughput	util
  1106 Kops	88.3%

• test frequent cgc calls with test_many_objects(@see src code) keep 20,000 objects alive:

  throughput	util
  5 Kops	68.3%

naming style:

• functions are named in snake case e.g. cgc_init.
• structures are named in pascal case e.g. Header.
• malloc are using snake upper case e.g. SIZE.

git commit log prefix:

• feat
• fix
• docs
• style
• refactor
• test