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Bug #10431

Updated by nobu (Nobuyoshi Nakada) almost 5 years ago

GC_ENABLE_LAZY_SWEEP=0と設定してrubyをビルドし,以下のコードを
実行した場合,GC時にオブジェクトが解放されていないように見えます.

~~~
$ ../configure CFLAGS="-DGC_ENABLE_LAZY_SWEEP=0" && make miniruby
$ cat bug2.rb
GC.disable
10000.times { Object.new }
total_freed_objects1 = GC.stat[:total_freed_objects]
GC.enable
GC.start(full_mark: true, immediate_sweep: true)
total_freed_objects2 = GC.stat[:total_freed_objects]
puts "freed object : #{total_freed_objects2 - total_freed_objects1}"

$ ./miniruby -v
ruby 2.2.0dev (2014-10-26 trunk 48073) [x86_64-darwin14]
$ ./miniruby bug2.rb
freed object : 0

~~~

また,rubyのコンパイルフラグをGC_ENABLE_LAZY_SWEEP=0,
RGENGC_CHECK_MODE=1と設定した上でビルドし,以下のコードを実行すると
assertで落ちます.

~~~
$ ./miniruby -e '10000.times { Object.new }'
Assertion failed: (objspace->flags.stat == gc_stat_none), function gc_start, file ../gc.c, line 5802.
[1] 91336 abort ./miniruby -e '10000.times { Object.new }'
~~~

sweepフェーズにてGC_ENABLE_LAZY_SWEEP!=1の時のみsweepが実行されるのが
原因のようですので,これを修正するパッチを作りました.

~~~diff ~~~
diff --git a/gc.c b/gc.c
index a27cc01..979e2e0 100644
--- a/gc.c
+++ b/gc.c
@@ -3314,9 +3314,8 @@ static void
gc_sweep_rest(rb_objspace_t *objspace)
{
rb_heap_t *heap = heap_eden; /* lazy sweep only for eden */
-
- if (is_lazy_sweeping(heap)) {
- while (is_lazy_sweeping(heap)) {
+ if ((heap)->sweep_pages != NULL) {
+ while ((heap)->sweep_pages != NULL) {
gc_sweep_step(objspace, heap);
}
}
~~~

English:

When I tried to compile ruby with GC_ENABLE_LAZY_SWEEP=0,
Ruby does not sweep objects immediatly.

~~~
$ ../configure CFLAGS="-DGC_ENABLE_LAZY_SWEEP=0" && make miniruby
$ cat bug2.rb
GC.disable
10000.times { Object.new }
total_freed_objects1 = GC.stat[:total_freed_objects]
GC.enable
GC.start(full_mark: true, immediate_sweep: true)
total_freed_objects2 = GC.stat[:total_freed_objects]
puts "freed object : #{total_freed_objects2 - total_freed_objects1}"

$ ./miniruby -v
ruby 2.2.0dev (2014-10-26 trunk 48073) [x86_64-darwin14]
$ ./miniruby bug2.rb
freed object : 0
~~~

In addition, when I set GC_ENABLE_LAZY_SWEEP=0 and RGENGC_CHECK_MODE=1
ruby gives me assertion error like this:

~~~
$ ./miniruby -e '10000.times { Object.new }'
Assertion failed: (objspace->flags.stat == gc_stat_none), function gc_start, file ../gc.c, line 5802.
[1] 91336 abort ./miniruby -e '10000.times { Object.new }'
~~~

The following patch fix this problem.

~~~diff ~~~
diff --git a/gc.c b/gc.c
index a27cc01..979e2e0 100644
--- a/gc.c
+++ b/gc.c
@@ -3314,9 +3314,8 @@ static void
gc_sweep_rest(rb_objspace_t *objspace)
{
rb_heap_t *heap = heap_eden; /* lazy sweep only for eden */
-
- if (is_lazy_sweeping(heap)) {
- while (is_lazy_sweeping(heap)) {
+ if ((heap)->sweep_pages != NULL) {
+ while ((heap)->sweep_pages != NULL) {
gc_sweep_step(objspace, heap);
}
}

~~~

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