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-rwxr-xr-xhyper/process/spawn103
1 files changed, 103 insertions, 0 deletions
diff --git a/hyper/process/spawn b/hyper/process/spawn
new file mode 100755
index 00000000..65e94d86
--- /dev/null
+++ b/hyper/process/spawn
@@ -0,0 +1,103 @@
+#! /bin/sh
+#
+# [sh -x] spawn [command [argument ...]]
+#
+# export id to create&destroy or reuse the working directory //proc/$id/.
+# this feature is for debug only and marked as deprecated, so don't rely
+# on it too hard.
+#
+spawn() {
+ set -euf
+
+ # establish working subdirectory in //proc. we're mking only
+ # transient dirs, i.e. if we mkdir, then we also defer rmdir.
+ if test -n "${id-}"; then
+ : "using id=$id from env"
+ wd=$pd/$id
+ if ! test -d $wd; then
+ : "make transient $wd/"
+ mkdir $wd
+ defer rmdir $wd
+ elif ! test `ls $wd | wc -l` = 0; then
+ : "$wd/ is not empty!"
+ exit 23
+ else
+ : "reuse existing $wd/"
+ fi
+ else
+ id=`cd $pd && mktemp -d XXXXXXXXXXXXXXXX`
+ wd=$pd/$id
+ defer rmdir $wd
+ : "made transient $wd/"
+ fi
+
+ # change to //proc working directory
+ cwd="$PWD"
+ cd $wd
+ defer cd $cwd
+
+ # create named pipes for the child process's stdio
+ mkfifo 0 1 2
+ defer rm 0 1 2
+
+ # spawn child process
+ ( : "in $PWD/ spawn ${*:-nothing}"
+ set +x # disable debug output so we don't clobber 2
+ exec 0>&- 1>&- 2>&- 0<>0 1<>1 2<>2
+ cd "$cwd"
+ exec "$@") &
+ pid=$!
+
+ # setup a trap to kill the child process if this (parent) process dies
+ defer kill $pid
+
+ # store misc. info.
+ ln -snf $cwd cwd
+ echo $id >id
+ echo $$ >ppid
+ echo $pid >pid
+ defer rm cwd id pid ppid
+
+ # wait for the child process's
+ set +e
+ wait $pid
+ code=$?
+ set -e
+
+ # the child is already dead
+ cancel kill $pid
+
+ # return the same way wait did
+ (exit $code)
+}
+
+#
+# defer [command [argument ...]]
+#
+# Defer execution of a command. Deferred commands are executed in LIFO
+# order immediately before the script terminates. See (golang's defer
+# statement for more information how this should work).
+#
+defer() {
+ defer="$*${defer+
+$defer}"
+}
+
+#
+# cancel [command [argument ...]]
+#
+# Cancel a deferred command. The arguments have to match exactly a
+# prior defer call or else chaos and mayhem shall haunt thee and shi-
+#
+cancel() {
+ defer="`echo "$defer" | grep -Fxv "$*"`"
+}
+
+# setup //proc directory
+pd=/tmp/krebs/proc
+mkdir -p $pd
+test -w $pd
+
+# setup deferred execution and spawn command
+trap 'eval "${defer-}"; defer=' EXIT INT TERM
+spawn "$@"