[Bug #20708] Retry `open` on EINTR

Co-Authored-By: Martin Dorey <martin.dorey@hds.com>

io.c

@@ -6956,7 +6956,10 @@ sysopen_func(void *ptr)
 static inline int
 rb_sysopen_internal(struct sysopen_struct *data)
 {
-    int fd = IO_WITHOUT_GVL_INT(sysopen_func, data);
+    int fd;
+    do {
+        fd = IO_WITHOUT_GVL_INT(sysopen_func, data);
+    } while (fd < 0 && errno == EINTR);
     if (0 <= fd)
         rb_update_max_fd(fd);
     return fd;

test/ruby/test_io.rb

@@ -3876,8 +3876,10 @@ __END__
   end
 
   def test_open_fifo_does_not_block_other_threads
-    mkcdtmpdir {
+    mkcdtmpdir do
       File.mkfifo("fifo")
+    rescue NotImplementedError
+    else
       assert_separately([], <<-'EOS')
         t1 = Thread.new {
           open("fifo", "r") {|r|
@@ -3892,8 +3894,32 @@ __END__
         t1_value, _ = assert_join_threads([t1, t2])
         assert_equal("foo", t1_value)
       EOS
-    }
-  end if /mswin|mingw|bccwin|cygwin/ !~ RUBY_PLATFORM
+    end
+  end
+
+  def test_open_fifo_restart_at_signal_intterupt
+    mkcdtmpdir do
+      File.mkfifo("fifo")
+    rescue NotImplementedError
+    else
+      wait = EnvUtil.apply_timeout_scale(0.1)
+      data = "writing to fifo"
+
+      # Do not use assert_separately, because reading from stdin
+      # prevents to reproduce [Bug #20708]
+      assert_in_out_err(["-e", "#{<<~"begin;"}\n#{<<~'end;'}"], [], [data])
+      wait, data = #{wait}, #{data.dump}
+      ;
+      begin;
+        trap(:USR1) {}
+        Thread.new do
+          sleep wait; Process.kill(:USR1, $$)
+          sleep wait; File.write("fifo", data)
+        end
+        puts File.read("fifo")
+      end;
+    end
+  end if Signal.list[:USR1] # Pointless on platforms without signal
 
   def test_open_flag
     make_tempfile do |t|