enter_chroot: speed up entering by backgrounding locale generation

Half of the current time is spent on calling locale-gen even when there is
nothing to be done (all locales already generated).  Throw it into the bg
to unblock the main thread.

BUG=None
TEST=`cros_sdk` still works
TEST=`LANG=et_EE.UTF-8 cros_sdk` generates the new locale in the background

Change-Id: Ibe9a07bec60a59cab1cf4230358f7f8ff5b21c2e
Reviewed-on: https://gerrit.chromium.org/gerrit/58041
Reviewed-by: David James <davidjames@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>

sdk_lib/enter_chroot.sh

@@ -197,6 +197,38 @@ promote_api_keys() {
   fi
 }
 
+generate_locales() {
+  # Make sure user's requested locales are available
+  # http://crosbug.com/19139
+  # And make sure en_US{,.UTF-8} are always available as
+  # that what buildbot forces internally
+  local l locales gen_locales=()
+
+  locales=$(printf '%s\n' en_US en_US.UTF-8 ${LANG} \
+    $LC_{ADDRESS,ALL,COLLATE,CTYPE,IDENTIFICATION,MEASUREMENT,MESSAGES} \
+    $LC_{MONETARY,NAME,NUMERIC,PAPER,TELEPHONE,TIME} | \
+    sort -u | sed '/^C$/d')
+  for l in ${locales}; do
+    if [[ ${l} == *.* ]]; then
+      enc=${l#*.}
+    else
+      enc="ISO-8859-1"
+    fi
+    case $(echo ${enc//-} | tr '[:upper:]' '[:lower:]') in
+    utf8) enc="UTF-8";;
+    esac
+    gen_locales+=("${l} ${enc}")
+  done
+  if [[ ${#gen_locales[@]} -gt 0 ]] ; then
+    # Force LC_ALL=C to workaround slow string parsing in bash
+    # with long multibyte strings.  Newer setups have this fixed,
+    # but locale-gen doesn't need to be run in any locale in the
+    # first place, so just go with C to keep it fast.
+    chroot "${FLAGS_chroot}" env LC_ALL=C locale-gen -q -u \
+      -G "$(printf '%s\n' "${gen_locales[@]}")"
+  fi
+}
+
 setup_env() {
   (
     flock 200
@@ -221,6 +253,9 @@ setup_env() {
       fi
     fi
 
+    # Do this early as it's slow and only needs basic mounts (above).
+    generate_locales &
+
     setup_mount "${FLAGS_trunk}" "--rbind" "${CHROOT_TRUNK_DIR}"
 
     debug "Setting up referenced repositories if required."
@@ -402,35 +437,6 @@ setup_env() {
     done
     promote_api_keys
 
-    # Make sure user's requested locales are available
-    # http://crosbug.com/19139
-    # And make sure en_US{,.UTF-8} are always available as
-    # that what buildbot forces internally
-    locales=$(printf '%s\n' en_US en_US.UTF-8 ${LANG} \
-      $LC_{ADDRESS,ALL,COLLATE,CTYPE,IDENTIFICATION,MEASUREMENT,MESSAGES} \
-      $LC_{MONETARY,NAME,NUMERIC,PAPER,TELEPHONE,TIME} | \
-      sort -u | sed '/^C$/d')
-    gen_locales=()
-    for l in ${locales}; do
-      if [[ ${l} == *.* ]]; then
-        enc=${l#*.}
-      else
-        enc="ISO-8859-1"
-      fi
-      case $(echo ${enc//-} | tr '[:upper:]' '[:lower:]') in
-        utf8) enc="UTF-8";;
-      esac
-      gen_locales=("${gen_locales[@]}" "${l} ${enc}")
-    done
-    if [[ ${#gen_locales[@]} -gt 0 ]] ; then
-      # Force LC_ALL=C to workaround slow string parsing in bash
-      # with long multibyte strings.  Newer setups have this fixed,
-      # but locale-gen doesn't need to be run in any locale in the
-      # first place, so just go with C to keep it fast.
-      chroot "$FLAGS_chroot" env LC_ALL=C locale-gen -q -u \
-        -G "$(printf '%s\n' "${gen_locales[@]}")"
-    fi
-
     # Fix permissions on shared memory to allow non-root users access to POSIX
     # semaphores.
     chmod -R 777 "${FLAGS_chroot}/dev/shm"