test/ruby/test_io.rb (test_select_leak): speedup and reduce memory use

We can reuse the sub-thread and exception with Thread#raise to
reproduce the old memory leak with less overhead.  This allows
us to to run more iterations and improve reliability of the
actual test, particularly on platforms without USE_THREAD_CACHE.

For glibc and jemalloc, also limit arena count to avoid
inadvertant growth.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64187 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_io.rb

@@ -3804,18 +3804,33 @@ __END__
 
   def test_select_leak
     skip 'MJIT uses too much memory' if RubyVM::MJIT.enabled?
-    assert_no_memory_leak([], <<-"end;", <<-"end;", rss: true, timeout: 60)
+    # avoid malloc arena explosion from glibc and jemalloc:
+    env = {
+      'MALLOC_ARENA_MAX' => '1',
+      'MALLOC_ARENA_TEST' => '1',
+      'MALLOC_CONF' => 'narenas:1',
+    }
+    assert_no_memory_leak([env], <<-"end;", <<-"end;", rss: true, timeout: 60)
       r, w = IO.pipe
       rset = [r]
       wset = [w]
+      exc = StandardError.new(-"select used to leak on exception")
+      exc.set_backtrace([])
       Thread.new { IO.select(rset, wset, nil, 0) }.join
     end;
-      20_000.times do
-        th = Thread.new { IO.select(rset, wset) }
-        Thread.pass until th.stop?
-        th.kill
-        th.join
+      th = Thread.new do
+        begin
+          IO.select(rset, wset)
+        rescue => e
+          retry
+        end while true
       end
+      50_000.times do
+        Thread.pass until th.stop?
+        th.raise(exc)
+      end
+      th.kill
+      th.join
     end;
   end
 end