Add FacetGuard

src/syndicate/actors.nim

@@ -685,3 +685,23 @@ proc run* =
       except CatchableError as err:
         stderr.writeLine "ioqueue continuation threw an error"
         raise err
+
+type FacetGuard* = object
+  facet: Facet
+
+proc initGuard*(f: Facet): FacetGuard =
+  result.facet = f
+  inc result.facet.inertCheckPreventers
+
+proc disarm*(g: var FacetGuard) =
+  if not g.facet.isNil:
+    assert g.facet.inertCheckPreventers > 0
+    dec g.facet.inertCheckPreventers
+    g.facet = nil
+
+proc `=destroy`*(g: var FacetGuard) =
+  disarm(g)
+
+proc `=copy`*(dst: var FacetGuard, src: FacetGuard) =
+  dst.facet = src.facet
+  inc dst.facet.inertCheckPreventers