test/ruby/test_thread.rb (test_fork_while_parent_locked): rewrite to avoid OOM

Instead of using a torture test, trigger the condition for the old
segfault in [Bug #15383] exactly.

[ruby-core:90676] [Bug #15430]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66508 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_thread.rb

@@ -1241,44 +1241,23 @@ q.pop
 
   def test_fork_while_parent_locked
     skip 'needs fork' unless Process.respond_to?(:fork)
-    require 'tempfile'
     m = Thread::Mutex.new
-    failures = 0
+    nr = 1
-    run = true
+    thrs = []
-    errs = ''
-    nr = 25 # reduce if more SIGKILL in tests
-    tmps = nr.times.map { Tempfile.new('Bug.15430.diagnosis') }
-    thrs = nr.times.map do |_i|
-      Thread.new(_i) do |i|
-        t = tmps[i]
-        t.sync = true
-        while run
-          pid = fork do
-            STDERR.reopen(t.path)
-            tmps.each(&:close)
-            m.synchronize {}
-          end
-          m.synchronize {}
-          _, st = Process.waitpid2(pid)
-          unless st.success?
     m.synchronize do
-              failures += 1
+      thrs = nr.times.map { Thread.new { m.synchronize {} } }
-              if errs.empty?
+      thrs.each { Thread.pass }
-                errs = st.inspect << t.read
+      pid = fork do
-                t.rewind
+        m.locked? or exit!(2)
+        thrs = nr.times.map { Thread.new { m.synchronize {} } }
+        m.unlock
+        thrs.each { |t| t.join(1) == t or exit!(1) }
+        exit!(0)
       end
+      _, st = Process.waitpid2(pid)
+      assert_predicate st, :success?, '[ruby-core:90312] [Bug #15383]'
     end
-          end
+    thrs.each { |t| assert_same t, t.join(1) }
-        end
-      end
-    end
-    sleep 0.5
-    run = false
-    thrs.each(&:join)
-    assert_empty errs, "lower `nr' if SIGKILL because of RLIMIT_NPROC limit"
-    assert_equal 0, failures, '[ruby-core:90312] [Bug #15383]'
-  ensure
-    tmps&.each(&:close!)
   end
 
   def test_fork_while_mutex_locked_by_forker