Bug #10431: Can't sweep garbage object immediatly when GC_ENABLE_LAZY_SWEEP=0

• Status: Closed
• Assignee: -
• Target version: 2.2.0
• ruby -v: ruby 2.2.0dev (2014-10-26 trunk 48073) [x86_64-darwin14]
• Backport: 2.0.0: DONTNEED, 2.1: DONTNEED

[imasahiro (Masahiro Ide)]

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 --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 --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);
        }
     }

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

r41510でis_lazy_sweeping()を使うようになり、その後r47444でis_lazy_sweeping()が変更されたときの見落としのようです。

[nobu (Nobuyoshi Nakada)]

• Backport changed from 2.0.0: UNKNOWN, 2.1: UNKNOWN to 2.0.0: DONTNEED, 2.1: DONTNEED

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

Applied in changeset r48150.

---

gc.c: fix no lazy sweep mode

• gc.c (gc_sweep_rest): sweep rest pages regardless of whether
  lazy sweep is enabled or not. based on the patch by Masahiro
  Ide at [ruby-dev:48706]. [Bug #10431]