From: Yui NARUSE <naruse@...>
Date: 2011-12-20T13:43:30+09:00
Subject: [ruby-dev:45011] [ruby-trunk - Bug #5768] TestRequire#test_race_exceptionで競合するケースがまだある


Issue #5768 has been updated by Yui NARUSE.


追いかけた結果、どうも lock に用いている rb_barrier_release/rb_barrier_destroy や rb_mutex_lock のマルチスレッド対応がいまいちだったようです。
前者は rb_mutex_unlock を外した直後から、待っていた他のスレッドが動き始めるのでもはや mutex->cond_waiting は古い情報となってしまう点、
後者は GVL_UNLOCK_BEGIN() した直後から、メインのスレッドが動いてしまう可能性があるのがダメですね。

diff --git a/test/ruby/test_require.rb b/test/ruby/test_require.rb
index 9186a6f..f1d8d12 100644
--- a/test/ruby/test_require.rb
+++ b/test/ruby/test_require.rb
@@ -350,9 +350,18 @@ class TestRequire < Test::Unit::TestCase
     path = tmp.path
     tmp.print <<-EOS
 TestRequire.scratch << :pre
-Thread.pass until t2 = TestRequire.scratch[1]
+TestRequire.scratch << Thread.current
+Thread.pass until t2 = TestRequire.scratch[2]
 Thread.pass until t2.stop?
-open(__FILE__, "w") {|f| f.puts "TestRequire.scratch << :post"}
+open(__FILE__, "w") do |f|
+  f.puts "t1, t2 = TestRequire.scratch[1, 2]"
+  f.puts "if Thread.current == t2"
+  f.puts "  TestRequire.scratch << :post"
+  f.puts "  until t1.stop?"
+  f.puts "    Thread.pass"
+  f.puts "  end"
+  f.puts "end"
+end
 raise "con1"
     EOS
     tmp.close
@@ -368,7 +377,6 @@ raise "con1"
         require(path)
       rescue RuntimeError
       end
-
       t1_res = require(path)
 
       Thread.pass until fin
@@ -376,7 +384,7 @@ raise "con1"
     end
 
     t2 = Thread.new do
-      Thread.pass until scratch[0]
+      Thread.pass until scratch[1]
       begin
         scratch << t2
         t2_res = require(path)
@@ -389,8 +397,8 @@ raise "con1"
     assert_nothing_raised(ThreadError, bug5754) {t1.join}
     assert_nothing_raised(ThreadError, bug5754) {t2.join}
 
-    assert_equal(true, (t1_res ^ t2_res), bug5754)
-    assert_equal([:pre, t2, :post, :t2, :t1], scratch, bug5754)
+    assert_equal(true, (t1_res ^ t2_res), bug5754 + " t1:#{t1_res} t2:#{t2_res}")
+    assert_equal([:pre, t1, t2, :post, :t2, :t1], scratch, bug5754)
   ensure
     tmp.close(true) if tmp
   end
diff --git a/thread.c b/thread.c
index ced10c2..c46653b 100644
--- a/thread.c
+++ b/thread.c
@@ -3409,7 +3409,6 @@ lock_func(rb_thread_t *th, rb_mutex_t *mutex, int timeout_ms)
     int interrupted = 0;
     int err = 0;
 
-    mutex->cond_waiting++;
     for (;;) {
 	if (!mutex->th) {
 	    mutex->th = th;
@@ -3438,7 +3437,6 @@ lock_func(rb_thread_t *th, rb_mutex_t *mutex, int timeout_ms)
 	    err = 0;
 	}
     }
-    mutex->cond_waiting--;
 
     return interrupted;
 }
@@ -3493,10 +3491,12 @@ rb_mutex_lock(VALUE self)
 	    if (vm_living_thread_num(th->vm) == th->vm->sleeper) {
 		timeout_ms = 100;
 	    }
+	    mutex->cond_waiting++;
 	    GVL_UNLOCK_BEGIN();
 	    interrupted = lock_func(th, mutex, timeout_ms);
 	    native_mutex_unlock(&mutex->lock);
 	    GVL_UNLOCK_END();
+	    mutex->cond_waiting--;
 
 	    reset_unblock_function(th, &oldubf);
 
@@ -3727,9 +3727,11 @@ rb_barrier_release(VALUE self)
 {
     VALUE mutex = GetBarrierPtr(self);
     rb_mutex_t *m;
-    rb_mutex_unlock(mutex);
+    int waiting;
     GetMutexPtr(mutex, m);
-    return m->cond_waiting > 0 ? Qtrue : Qfalse;
+    waiting = m->cond_waiting;
+    rb_mutex_unlock(mutex);
+    return waiting > 0 ? Qtrue : Qfalse;
 }
 
 /*
@@ -3740,10 +3742,12 @@ rb_barrier_destroy(VALUE self)
 {
     VALUE mutex = GetBarrierPtr(self);
     rb_mutex_t *m;
+    int waiting;
     DATA_PTR(self) = 0;
-    rb_mutex_unlock(mutex);
     GetMutexPtr(mutex, m);
-    return m->cond_waiting > 0 ? Qtrue : Qfalse;
+    waiting = m->cond_waiting;
+    rb_mutex_unlock(mutex);
+    return waiting > 0 ? Qtrue : Qfalse;
 }
 
 int
----------------------------------------
Bug #5768: TestRequire#test_race_exceptionで競合するケースがまだある
https://bugs.ruby-lang.org/issues/5768

Author: Yui NARUSE
Status: Assigned
Priority: Normal
Assignee: Nobuyoshi Nakada
Category: 
Target version: 
ruby -v: ruby 2.0.0dev (2011-12-16 trunk 34058) [x86_64-freebsd9.0]


まだrequireで競合するケースが残っています。
現在のテストだと確率的にしか起きませんが、以下の通り変更すると確実に起きるようになります。

diff --git a/test/ruby/test_require.rb b/test/ruby/test_require.rb
index 9186a6f..262a5ef 100644
--- a/test/ruby/test_require.rb
+++ b/test/ruby/test_require.rb
@@ -352,7 +352,7 @@ class TestRequire < Test::Unit::TestCase
 TestRequire.scratch << :pre
 Thread.pass until t2 = TestRequire.scratch[1]
 Thread.pass until t2.stop?
-open(__FILE__, "w") {|f| f.puts "TestRequire.scratch << :post"}
+open(__FILE__, "w") {|f| f.puts "TestRequire.scratch << :post"; f.puts "t1,t2=TestRequire.scratch[1, 2];if Thread.current == t2; Thread.pass until t1.stopped?; end"}
 raise "con1"
     EOS
     tmp.close
@@ -364,6 +364,7 @@ raise "con1"
     t2_res = nil
 
     t1 = Thread.new do
+      scratch << t1
       begin
         require(path)
       rescue RuntimeError
@@ -389,8 +390,8 @@ raise "con1"
     assert_nothing_raised(ThreadError, bug5754) {t1.join}
     assert_nothing_raised(ThreadError, bug5754) {t2.join}
 
-    assert_equal(true, (t1_res ^ t2_res), bug5754)
-    assert_equal([:pre, t2, :post, :t2, :t1], scratch, bug5754)
+    assert_equal(true, (t1_res ^ t2_res), bug5754 + " t1:#{t1_res} t2:#{t2_res}")
+    assert_equal([:pre, t1, t2, :post, :t2, :t1], scratch, bug5754)
   ensure
     tmp.close(true) if tmp
   end


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