gc: make generational mode of Boehm-GC available (#9514)

cmd/v/help/build-c.txt

@@ -71,10 +71,16 @@ see also `v help build`.
       more performant without autofree.
       
    -gc <mode>
-      Use and link an optional garbage collector. 
-      Only `-gc boehm` and `-gc boehm_leak` are supported currently.
-      You need to install a `libgc-dev` package first, or install it manually
-      from source: 
+      Use and link an optional garbage collector. Only tThe Boehm–Demers–Weiser
+      garbage collector is supported currently with the following sub-options:
+
+      `-gc boehm` ........ selects the default mode for the architecture
+      `-gc boehm_full` ... full garbage collection mode
+      `-gc boehm_incr` ... incremental/generational garbage collection mode
+      `-gc boehm_leak` ... leak detection mode
+
+      You need to install a `libgc-dev` package first, or install it manually from:
+
           https://github.com/ivmai/bdwgc
           
       Note, `-gc boehm` is complementary to -autofree. The Boehm garbage

vlib/v/gen/c/cgen.v

@@ -423,7 +423,7 @@ pub fn (mut g Gen) init() {
 		}
 		g.comptime_defines.writeln('')
 	}
-	if g.pref.gc_mode in [.boehm, .boehm_leak] {
+	if g.pref.gc_mode in [.boehm_full, .boehm_incr, .boehm, .boehm_leak] {
 		g.comptime_defines.writeln('#define _VGCBOEHM (1)')
 	}
 	if g.pref.is_debug || 'debug' in g.pref.compile_defines {

vlib/v/gen/c/cmain.v

@@ -67,12 +67,15 @@ fn (mut g Gen) gen_c_main_function_header() {
 
 fn (mut g Gen) gen_c_main_header() {
 	g.gen_c_main_function_header()
-	if g.pref.gc_mode in [.boehm, .boehm_leak] {
+	if g.pref.gc_mode in [.boehm_full, .boehm_incr, .boehm, .boehm_leak] {
 		g.writeln('#if defined(_VGCBOEHM)')
 		if g.pref.gc_mode == .boehm_leak {
 			g.writeln('\tGC_set_find_leak(1);')
 		}
 		g.writeln('\tGC_INIT();')
+		if g.pref.gc_mode == .boehm_incr {
+			g.writeln('\tGC_enable_incremental();')
+		}
 		g.writeln('#endif')
 	}
 	g.writeln('\t_vinit(___argc, (voidptr)___argv);')
@@ -158,12 +161,15 @@ pub fn (mut g Gen) gen_c_main_for_tests() {
 	main_fn_start_pos := g.out.len
 	g.writeln('')
 	g.gen_c_main_function_header()
-	if g.pref.gc_mode in [.boehm, .boehm_leak] {
+	if g.pref.gc_mode in [.boehm_full, .boehm_incr, .boehm, .boehm_leak] {
 		g.writeln('#if defined(_VGCBOEHM)')
 		if g.pref.gc_mode == .boehm_leak {
 			g.writeln('\tGC_set_find_leak(1);')
 		}
 		g.writeln('\tGC_INIT();')
+		if g.pref.gc_mode == .boehm_incr {
+			g.writeln('\tGC_enable_incremental();')
+		}
 		g.writeln('#endif')
 	}
 	g.writeln('\t_vinit(___argc, (voidptr)___argv);')

vlib/v/pref/pref.v

@@ -19,8 +19,10 @@ pub enum BuildMode {
 
 pub enum GarbageCollectionMode {
 	no_gc
-	boehm
-	boehm_leak
+	boehm_full // full garbage collection mode
+	boehm_incr // incremental garbage colletion mode
+	boehm // default Boehm-GC mode for architecture
+	boehm_leak // leak detection mode (makes `gc_check_leaks()` work)
 }
 
 pub enum OutputMode {
@@ -159,7 +161,7 @@ pub mut:
 	build_options       []string // list of options, that should be passed down to `build-module`, if needed for -usecache
 	cache_manager       vcache.CacheManager
 	is_help             bool // -h, -help or --help was passed
-	gc_mode             GarbageCollectionMode = .no_gc // .no_gc, .boehm, .boehm_leak
+	gc_mode             GarbageCollectionMode = .no_gc // .no_gc, .boehm, .boehm_leak, ...
 	// checker settings:
 	checker_match_exhaustive_cutoff_limit int = 10
 }
@@ -227,6 +229,16 @@ pub fn parse_args(known_external_commands []string, args []string) (&Preferences
 					'' {
 						res.gc_mode = .no_gc
 					}
+					'boehm_full' {
+						res.gc_mode = .boehm_full
+						parse_define(mut res, 'gcboehm')
+						parse_define(mut res, 'gcboehm_full')
+					}
+					'boehm_incr' {
+						res.gc_mode = .boehm_incr
+						parse_define(mut res, 'gcboehm')
+						parse_define(mut res, 'gcboehm_incr')
+					}
 					'boehm' {
 						res.gc_mode = .boehm
 						parse_define(mut res, 'gcboehm')
@@ -237,7 +249,7 @@ pub fn parse_args(known_external_commands []string, args []string) (&Preferences
 						parse_define(mut res, 'gcboehm_leak')
 					}
 					else {
-						eprintln('unknown garbage collection mode, only `-gc boehm` and `-gc boehm_leak` are supported')
+						eprintln('unknown garbage collection mode, only `-gc boehm`, `-gc boehm_incr`, `-gc boehm_full` and `-gc boehm_leak` are supported')
 						exit(1)
 					}
 				}

vlib/v/tests/bench/gcboehm/GC_bench.plt

@@ -0,0 +1,9 @@
+#!/usr/bin/gnuplot -persist
+set title "Boehm-GC: Full vs. Incremental/Generational Mode" 
+set xlabel "Interval #" 
+set ylabel "Pause Time [ms]" 
+set terminal pdfcairo  transparent enhanced fontscale 0.5 size 5.00in, 3.00in 
+set output "GC_bench.pdf"
+plot "boehm_full.txt" title "full GC" w i, "boehm_incr.txt" title "incr/generational GC" w i
+set output
+#    EOF

vlib/v/tests/bench/gcboehm/GC_bench.v

@@ -0,0 +1,46 @@
+import time
+import rand
+import math
+
+struct MemObj {
+mut:
+	nxt []&MemObj
+}
+
+const (
+	log2n = 10
+	n     = 1 << log2n
+	n4    = f64(u64(1) << (4 * log2n))
+)
+
+fn waste_mem() {
+	mut objs := MemObj{
+		nxt: []&MemObj{len: n}
+	}
+	for {
+		sz := rand.int_in_range(10, 100000)
+		mut new_obj := &MemObj{
+			nxt: []&MemObj{len: sz}
+		}
+		sz2 := rand.int_in_range(10, 100000)
+		new_obj2 := &MemObj{
+			nxt: []&MemObj{len: sz2}
+		}
+		idx2 := rand.int_in_range(0, sz / 2)
+		new_obj.nxt[idx2] = new_obj2
+		// non-equally distributed random index
+		idx := int(math.sqrt(math.sqrt(rand.f64n(n4))))
+		objs.nxt[idx] = new_obj
+	}
+}
+
+fn main() {
+	go waste_mem()
+	mut last := time.sys_mono_now()
+	for _ in 0 .. 10_000_000 {
+		now := time.sys_mono_now()
+		interval := now - last
+		println(f64(interval) / f64(time.millisecond))
+		last = now
+	}
+}

vlib/v/tests/bench/gcboehm/Makefile

@@ -0,0 +1,26 @@
+.PHONY: all
+
+all: GC_bench.pdf
+
+GC_bench.pdf: boehm_full.txt boehm_incr.txt
+	gnuplot GC_bench.plt
+	@echo "$@ created"
+
+boehm_full.txt: GC_bench_full
+	sync
+	sleep 1
+	./$< > $@
+
+boehm_incr.txt: GC_bench_incr
+	sync
+	sleep 1
+	./$< > $@
+
+GC_bench_full: GC_bench.v
+	v -prod -gc boehm_full -o $@ $<
+
+GC_bench_incr: GC_bench.v
+	v -prod -gc boehm_incr -o $@ $<
+
+clean:
+	rm -f boehm_full.txt boehm_incr.txt GC_bench.pdf GC_bench_full GC_bench_incr