Index: openacs-4/packages/acs-tcl/tcl/request-processor-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/request-processor-procs.tcl,v
diff -u -N -r1.153.2.16 -r1.153.2.17
--- openacs-4/packages/acs-tcl/tcl/request-processor-procs.tcl	26 Dec 2019 14:43:50 -0000	1.153.2.16
+++ openacs-4/packages/acs-tcl/tcl/request-processor-procs.tcl	18 May 2020 21:13:20 -0000	1.153.2.17
@@ -1866,9 +1866,9 @@
     Maps a hostname to the corresponding sub-directory.
 
 } {
-    set key ::acs::root_of_host($host)
-    if {[info exists $key]} {return [set $key]}
-    set $key [acs::root_of_host_noncached $host]
+    return [acs::per_thread_cache eval -key acs-tcl:root_of_host($host) {
+        acs::root_of_host_noncached $host
+    }]
 }