From: Paul Hänsch <paul@plutz.net>
Date: Sun, 15 Jul 2018 12:07:22 +0000 (+0200)
Subject: locking functions
X-Git-Url: https://git.plutz.net/?a=commitdiff_plain;h=aa4821bae04b2022828cbbb725874db96ca249fd;p=clickslide

locking functions
---

diff --git a/storage.sh b/storage.sh
index bf8b7b9..d4fbca3 100755
--- a/storage.sh
+++ b/storage.sh
@@ -17,57 +17,63 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with CGIlite.  If not, see <http://www.gnu.org/licenses/>. 
 
-# ksh and zsh workaround
-case "${0##*/}" in
-  zsh) setopt -o OCTAL_ZEROES 2>&- ;; # zsh, mostly ignored by other shells
-  ksh) set -o posix ;;                # ksh, will crash most other shells
-esac
+LOCK(){
+  lock="${1}.lock"
+  timeout="${2-20}"
+  if [ \! -w "${lock%/*}" ] || [ -e "$lock" -a \! -d "$lock" ]; then
+    printf 'Impossible to get lock: %s\n' "$lock" >&2
+    return 1
+  fi
 
-STORE(){
-  # Store fields from a HTTP GET or POST string in a file
-  # usage: STORE "${QUERY_STRING}"
-  #    or: STORE "$(head -n $HTTP_CONTENT_LENGTH)"
-  # backslashes and newline characters will be escaped in field values,
-  # the escape symbol is a backslash
-  # hexadecimal character descriptions (%00 - %FF) will be expanded
-  # the + character will be converted to [space]
-  # one line in the output corresponds to exactly one field, so you can
-  # use grep to filter which fields of a query should be stored
-  printf "$(
-  printf '%s' "$@" \
-  | sed -r ':X; $bY; N; bX; :Y;
-            s;\+; ;g; s;(\\|5[Cc]);\\\\\\\\;g; s;(\n|%0[Aa]);\\\\n;g; s;(^|&)([^=]+)=;\1\2:;g; s;&;\n;g;
-            s;^\n+;;; s;$;\\n;; s;\n+;\n;g;
-            # Hexadecimal { %00 - %FF } will be transformed to octal { \000 - \377 } for posix printf
-            s;%[0123].;&\\0;g; s;%[4567].;&\\1;g; s;%[89AB].;&\\2;g; s;%[CDEF].;&\\3;g;
-            s;%[048C][0-7]\\.;&0;g; s;%[048C][89A-F]\\.;&1;g; s;%[159D][0-7]\\.;&2;g; s;%[159D][89A-F]\\.;&3;g;
-            s;%[26AE][0-7]\\.;&4;g; s;%[26AE][89A-F]\\.;&5;g; s;%[37BF][0-7]\\.;&6;g; s;%[37BF][89A-F]\\.;&7;g;
-            s;%.[08](\\..);\10;g; s;%.[19](\\..);\11;g; s;%.[2A](\\..);\12;g; s;%.[3B](\\..);\13;g;
-            s;%.[4C](\\..);\14;g; s;%.[5D](\\..);\15;g; s;%.[6E](\\..);\16;g; s;%.[7F](\\..);\17;g;
-           ' 
-  )"
+  while ! mkdir "$lock"; do
+    block="$(cat "$lock/pid" || printf 1)"
+    if ! { ps -eo pid |grep -qwF "$block"; }; then
+      printf 'Overriding stale lock: %s\n' "$lock" >&2
+      break
+    fi
+    if [ $timeout -le 0 ]; then
+      printf 'Timeout while trying to get lock: %s\n' "$lock" >&2
+      return 1
+    fi
+    timeout=$((timeout - 1))
+    sleep 1
+  done
+  printf '%i\n' $$ >"${lock}/pid"
+  return 1
 }
 
-LOAD(){
-  # read a file written by STORE and assign all fields to variables
-  # usage: eval "$(LOAD <file)"
-  #
-  # fields will be assigned to shell variables of the same name, but with the following constraints:
-  # * small letters will be converted to capitals
-  # * all non-alphanumeric characters will be converted to underscore (_)
-  # * an underscore will be prepended
-  # as a consequence variable names are guaranteed to match the regex /_[A-Z0-9_]+/
-  #
-  # field values may contain any character, proper escaping for safe use in eval is taken care of
-  # Your shell may or may not purge certain binary characters from variable values during processing
+RELEASE(){
+  lock="${1}.lock"
+  if [ "$(cat "$lock/pid")" = "$$" ]; then
+    rm "$lock/pid"
+    if ! rmdir "$lock"; then
+      printf 'Cannot remove tainted lock: %s\n' "$lock" >&2
+      printf '%i\n' $$ >"${lock}/pid"
+      return 1
+    fi
+  else
+    printf 'Refusing to release foreign lock: %s\n' "$lock" >&2
+    return 1
+  fi
+}
+
+STRING(){
+  printf %s "$*" |sed -r '
+    :X; $!{N;bX;}
+    s;\\;\\\\;g;
+    s;\n;\\n;g;
+    s;\t;\\t;g;
+    s;\r;\\r;g;
+  '
+}
 
-  sed -r 'h; s;^[^:]+:;;
-          s;'\'';'\''\\'\'\'';g;
-          s;^.*$;'\''&'\'';;
-          s;\\n;\n;g;
-          x; s;^([^:]+):.*$;\1;
-          y;abcdefghijklmnopqrstuvwxyz;ABCDEFGHIJKLMNOPQRSTUVWXYZ;
-          s;[^A-Z0-9_];_;g; s;^.*$;_&=;;
-          G; s;^([A-Z0-9_]+=)\n;\1;;
-         '
+UNSTRING(){
+  printf %s "$*" |sed -r '
+    :X
+    s;((^|[^\\])(\\\\)*)\\n;\1\n;g;
+    s;((^|[^\\])(\\\\)*)\\t;\1\t;g;
+    s;((^|[^\\])(\\\\)*)\\r;\1\r;g;
+    tX;
+    s;\\\\;\\;g;
+  '
 }