rescan: abort current scan if a new one is scheduled

It is possible to queue up a rescans by adding or removing
session items quickly. There is no use in running them all, I think. We
can abort and just run the last one.

Change-Id: Ie7df601d0ea5aada64aa65a09824fcb89e15ee81

src/scripts/linking/rescan.lua

@@ -17,6 +17,8 @@ log = Log.open_topic ("s-linking")
 handles = {}
 handles.rescan_enabled = true
 handles.timeout_source = nil
+handles.rescan_active = false
+handles.rescan_abort_current = false
 
 function checkFilter (si, om, handle_nonstreams)
   -- always handle filters if handle_nonstreams is true, even if it is disabled
@@ -163,6 +165,12 @@ function handleLinkables (source)
   local om = source:call ("get-object-manager", "session-item")
 
   for si in om:iterate { type = "SiLinkable" } do
+    -- Check if we should abort this rescan
+    if handles.rescan_abort_current then
+      handles.rescan_abort_current = false
+      return
+    end
+
     if not checkLinkable (si, om) then
       goto skip_linkable
     end
@@ -195,6 +203,8 @@ SimpleEventHook {
     local source = event:get_source ()
     local om = source:call ("get-object-manager", "session-item")
 
+    handles.rescan_active = true
+
     log:info ("rescanning...")
 
     -- always unlink all filters that are smart and disabled
@@ -212,6 +222,8 @@ SimpleEventHook {
     end
 
     handleLinkables (source)
+
+    handles.rescan_active = false
   end
 }:register ()
 
@@ -244,7 +256,13 @@ SimpleEventHook {
   execute = function (event)
     if handles.rescan_enabled then
       local source = event:get_source ()
+
+      if handles.rescan_active then
+        handles.rescan_abort_current = true
+      end
+
       source:call ("schedule-rescan", "linking")
+      handles.rescan_active = true
     end
   end
 }:register ()