Add lib/bash/subshell.sh and use in pt-stalk to fix/improve subprocess waiting.

lib/bash/subshell.sh

@@ -0,0 +1,66 @@
+# This program is copyright 2013 Percona Ireland Ltd.
+# Feedback and improvements are welcome.
+#
+# THIS PROGRAM IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
+# WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+# MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation, version 2; OR the Perl Artistic License.  On UNIX and similar
+# systems, you can issue `man perlgpl' or `man perlartistic' to read these
+# licenses.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program; if not, write to the Free Software Foundation, Inc., 59 Temple
+# Place, Suite 330, Boston, MA  02111-1307  USA.
+# ###########################################################################
+# subshell package
+# ###########################################################################
+
+# Package: subshell
+
+set -u
+
+wait_for_subshells() {
+   local max_wait=$1
+   if [ "$(jobs)" ]; then
+      log "Waiting up to $max_wait seconds for subprocesses to finish..."
+      local slept=0
+      while [ -n "$(jobs)" ]; do
+         local subprocess_still_running=""
+         for pid in $(jobs -p); do
+            if kill -0 $pid >/dev/null 2>&1; then
+               subprocess_still_running=1
+            fi
+         done
+         if [ "$subprocess_still_running" ]; then
+            sleep 1
+            slept=$((slept + 1))
+            [ $slept -ge $max_wait ] && break
+         else
+            break
+         fi
+      done
+   fi
+}
+
+kill_all_subshells() {
+   if [ "$(jobs)" ]; then
+      for pid in $(jobs -p); do
+         if kill -0 $pid >/dev/null 2>&1; then
+            # This isn't an warning (we don't want exit status 1) because
+            # the system may be running slowly so it's just "natural" that
+            # a collector may get stuck or run really slowly.
+            log "Killing subprocess $pid"
+            kill $pid >/dev/null 2>&1
+         fi
+      done
+   else
+      log "All subprocesses have finished"
+   fi
+}
+
+# ###########################################################################
+# End subshell package
+# ###########################################################################