fix domain pool: block signals in background threads

close #35

src/dpool/moonpool_dpool.ml

@@ -96,6 +96,11 @@ let domains_ : (worker_state option * Domain_.t option) Lock.t array =
      in a tight loop), and if nothing happens it tries to stop to free resources.
 *)
 let work_ idx (st : worker_state) : unit =
+  Thread.sigmask SIG_BLOCK
+    [
+      Sys.sigpipe; Sys.sigbus; Sys.sigterm; Sys.sigint; Sys.sigusr1; Sys.sigusr2;
+    ]
+  |> ignore;
   let main_loop () =
     let continue = ref true in
     while !continue do