Introduce socket shutdown into connection type, used if a fork is active (#11376)

Introduce socket `shutdown()` into connection type, and use it
on normal socket if a fork is active. This allows us to close
client connections when there are child processes sharing the
file descriptors.

Fixes #10077. The reason is that since the `fork()` child is holding
the file descriptors, the `close` in `unlinkClient -> connClose`
isn't sufficient. The client will not realize that the connection is
disconnected until the child process ends.

Let's try to be conservative and only use shutdown when the fork is active.

1 files changed, 38 insertions, 0 deletions

diff --git a/tests/unit/introspection.tcl b/tests/unit/introspection.tcl
index 73f1649a7..25e46d6ab 100644
--- a/tests/unit/introspection.tcl
+++ b/tests/unit/introspection.tcl
@@ -54,6 +54,44 @@ start_server {tags {"introspection"}} {
         # After killing `me`, the first ping will throw an error
         assert_error "*I/O error*" {r ping}
         assert_equal "PONG" [r ping]
+
+        $rd1 close
+        $rd2 close
+        $rd3 close
+        $rd4 close
+    }
+
+    test "CLIENT KILL close the client connection during bgsave" {
+        # Start a slow bgsave, trigger an active fork.
+        r flushall
+        r set k v
+        r config set rdb-key-save-delay 10000000
+        r bgsave
+        wait_for_condition 1000 10 {
+            [s rdb_bgsave_in_progress] eq 1
+        } else {
+            fail "bgsave did not start in time"
+        }
+
+        # Kill (close) the connection
+        r client kill skipme no
+
+        # In the past, client connections needed to wait for bgsave
+        # to end before actually closing, now they are closed immediately.
+        assert_error "*I/O error*" {r ping} ;# get the error very quickly
+        assert_equal "PONG" [r ping]
+
+        # Make sure the bgsave is still in progress
+        assert_equal [s rdb_bgsave_in_progress] 1
+
+        # Stop the child before we proceed to the next test
+        r config set rdb-key-save-delay 0
+        r flushall
+        wait_for_condition 1000 10 {
+            [s rdb_bgsave_in_progress] eq 0
+        } else {
+            fail "bgsave did not stop in time"
+        }
     }
 
     test {MONITOR can log executed commands} {