From ad77048a396bcf78633abd15aa4ade9cb4bed8a9 Mon Sep 17 00:00:00 2001
From: Ramana Kumar <ramana@member.fsf.org>
Date: Thu, 9 Nov 2017 09:07:17 +1100
Subject: [PATCH] Add helper utility for acquiring the lock

For running commands alongside the server without interfering with its
operation.
---
 flock.sml | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 flock.sml

diff --git a/flock.sml b/flock.sml
new file mode 100644
index 0000000..ff2f606
--- /dev/null
+++ b/flock.sml
@@ -0,0 +1,27 @@
+(*
+  Acquire the lock that is used by the server to run a command without
+  interfering with the server
+*)
+use "regressionLib.sml";
+open regressionLib
+open Posix.Process
+fun main () =
+  let
+    val args = CommandLine.arguments ()
+    val () = assert (not (List.null args)) ["usage: ./flock cmd args ..."]
+    val fd = acquire_lock ()
+  in
+    case fork() of
+      NONE => execp (List.hd args, args)
+    | SOME pid =>
+      let
+        val (pid',status) = wait ()
+        val () = assert (pid=pid') ["wrong child"]
+        val () = Posix.IO.close fd
+      in
+        case status of
+          W_EXITED => ()
+        | W_EXITSTATUS w => exit w
+        | _ => exit (Word8.fromInt 126)
+      end
+  end