4 files changed, 43 insertions, 7 deletions
diff --git a/Functions/Calendar/calendar b/Functions/Calendar/calendar
index f6316eb18..b87a14628 100644
--- a/Functions/Calendar/calendar
+++ b/Functions/Calendar/calendar
@@ -253,13 +253,21 @@ if (( verbose )); then
   fi
 fi
 
+# start of subshell for OS file locking
+(
 # start of block for following always to clear up lockfiles.
+# Not needed but harmless if OS file locking is used.
 {
   if [[ -n $donefile ]]; then
     # Attempt to lock both $donefile and $calendar.
     # Don't lock $newfile; we've tried our best to make
     # the name unique.
-    calendar_lockfiles $calendar $donefile || return 1
+    if zmodload -F zsh/system b:zsystem && zsystem supports flock; then
+      zsystem flock $calendar
+      zsystem flock $donefile
+    else
+      calendar_lockfiles $calendar $donefile || exit 1
+    fi
   fi
 
   calendar_read $calendar
@@ -414,4 +422,5 @@ Old calendar left in $calendar.old." >&2
   (( ${#lockfiles} )) && rm -f $lockfiles
 }
 
-return $rstat
+exit $rstat
+)
diff --git a/Functions/Calendar/calendar_add b/Functions/Calendar/calendar_add
index 280e5f365..ac5caecd7 100644
--- a/Functions/Calendar/calendar_add
+++ b/Functions/Calendar/calendar_add
@@ -68,9 +68,18 @@ if [[ $addline = ${~uidpat} ]]; then
   my_uid=${(U)match[1]}
 fi
 
+# start of subshell for OS file locking
+(
 # start of block for following always to clear up lockfiles.
+# Not needed but harmless if OS file locking is used.
 {
-  (( nolock )) || calendar_lockfiles $calendar || return 1
+  if (( ! nolock )); then
+    if zmodload -F zsh/system b:zsystem && zsystem supports flock; then
+      zsystem flock $calendar
+    else
+      calendar_lockfiles $calendar || exit 1
+    fi
+  fi
 
   if [[ -f $calendar ]]; then
     calendar_read $calendar
@@ -158,4 +167,5 @@ Old calendar left in $calendar.old." >&2
   (( ${#lockfiles} )) && rm -f $lockfiles
 }
 
-return $rstat
+exit $rstat
+)
diff --git a/Functions/Calendar/calendar_edit b/Functions/Calendar/calendar_edit
index e31decb76..e3ac5c39b 100644
--- a/Functions/Calendar/calendar_edit
+++ b/Functions/Calendar/calendar_edit
@@ -10,12 +10,21 @@ done
 
 zstyle -s ':datetime:calendar:' calendar-file calendar || calendar=~/calendar
 
+# start of subshell for OS file locking
+(
+# start of block for following always to clear up lockfiles.
+# Not needed but harmless if OS file locking is used.
 {
-  calendar_lockfiles $calendar || return 1
+  if zmodload -F zsh/system b:zsystem && zsystem supports flock; then
+    zsystem flock $calendar
+  else
+    calendar_lockfiles $calendar || exit 1
+  fi
 
   eval $editor \$calendar
 } always {
   (( ${#lockfiles} )) && rm -f $lockfiles
 }
+)
 
 (( cal_running )) && calendar -s
diff --git a/Functions/Calendar/calendar_sort b/Functions/Calendar/calendar_sort
index 7d346efc1..4911e34a2 100644
--- a/Functions/Calendar/calendar_sort
+++ b/Functions/Calendar/calendar_sort
@@ -11,9 +11,16 @@ integer i
 # Read the calendar file from the calendar-file style
 zstyle -s ':datetime:calendar:' calendar-file calendar || calendar=~/calendar
 
-# Start block for "always" to handle lockfile
+# start of subshell for OS file locking
+(
+# start of block for following always to clear up lockfiles.
+# Not needed but harmless if OS file locking is used.
 {
-  calendar_lockfiles $calendar || return 1
+  if zmodload -F zsh/system b:zsystem && zsystem supports flock; then
+    zsystem flock $calendar
+  else
+    calendar_lockfiles $calendar || exit 1
+  fi
 
   new=$calendar.new.$$
   calendar_read $calendar
@@ -65,3 +72,4 @@ Old calendar left in $calendar.old"
 } always {
   (( ${#lockfiles} )) && rm -rf $lockfiles
 }
+)