Use Util.with_mutex/Util.with_mutex0 to avoid unbalanced locking

TODO

@@ -1,5 +0,0 @@
-Running the server and test3_latency, and then starting and
-interrupting test1_latency repeatedly, the server eventually corrupts
-itself and will no longer let test1_latency bind and receive
-messages. Sometimes test3_latency stops too.
-  [TENTATIVE FIX: see try/with in write_sexp in relay.ml]

log.ml

@@ -3,10 +3,12 @@ open Sexp
 let mtx = Mutex.create ()
 let write_to_log label body =
   Mutex.lock mtx;
-  print_string label;
-  print_string ": ";
-  output_sexp_human stdout body;
-  print_newline ();
+  (try
+    print_string label;
+    print_string ": ";
+    output_sexp_human stdout body;
+    print_newline ()
+  with _ -> ());
   Mutex.unlock mtx
 
 let hook = ref write_to_log

relay.ml

@@ -42,9 +42,7 @@ let flush_output mtx flush_control cout =
     match Event.poll (Event.receive flush_control) with
     | Some () -> ()
     | None ->
-	Mutex.lock mtx;
-	let ok = try flush cout; true with _ -> false in
-	Mutex.unlock mtx;
+	let ok = Util.with_mutex0 mtx (fun () -> try flush cout; true with _ -> false) in
 	if ok then (Thread.delay 0.1; loop ()) else ()
   in loop ()
 
@@ -59,11 +57,7 @@ let relay_main peername cin cout =
 			Str "", Str "",
 			Str "", Str ""));
   let mtx = Mutex.create () in
-  let write_sexp s =
-    Mutex.lock mtx;
-    (try output_sexp cout s with Sys_error _ -> ()); (* TODO: try removing this *)
-    Mutex.unlock mtx
-  in
+  let write_sexp = Util.with_mutex mtx (output_sexp cout) in
   let flush_control = Event.new_channel () in
   ignore (Util.create_thread (endpoint_name peername ^ " flush") None
 	    (flush_output mtx flush_control) cout);

util.ml

@@ -15,3 +15,15 @@ let create_thread name cleanup main initarg =
       | None -> ())
   in
   Thread.create guarded_main initarg
+
+let with_mutex m f arg =
+  Mutex.lock m;
+  try
+    let result = f arg in
+    Mutex.unlock m;
+    result
+  with e ->
+    Mutex.unlock m;
+    raise e
+
+let with_mutex0 m thunk = with_mutex m thunk ()