Cause make start to wait for master start.

masters/master-common-rules.mk

 # -*- makefile -*-
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This should be included by a makefile which lives in a buildmaster/buildslave
 # directory (next to the buildbot.tac file). That including makefile *must*
 # define MASTERPATH.
 
 # The 'start' and 'stop' targets start and stop the buildbot master.
@@ skipping 45 matching lines @@
         $(GCLIENT) diff >> actions.log || true
         @($(INFRA_RUNPY) infra.tools.send_monitoring_event \
                    --service-event-revinfo=$(CURRENT_DIR)/revinfo.log \
                    --service-event-type=START \
                    --event-mon-run-type=prod \
                    --event-mon-service-name \
                    buildbot/master/$(MASTERPATH) \
    || echo 'Running send_monitoring_event failed, skipping sending events.' \
   ) 2>&1 | tee -a actions.log
 endif
+        # There is a race condition between startup and when twistd.pid is written.
+        # Anyone issuing a second `make start` before the twistd.pid is written will
+        # spawn two masters. This is hopefully unlikely, but a proper solution would
+        # be to use flock (not available on OSX). The critical section contains BOTH
+        # the twistd start and the wait for the twistd.pid.
         @echo 'Now running Buildbot master.'
         PYTHONPATH=$(PYTHONPATH) python $(SCRIPTS_DIR)/common/twistd --no_save -y buildbot.tac
+        @echo 'Waiting for creation of twistd.pid...'
+        while `test ! -f twistd.pid`; do sleep 1; done;

[dsansome, 2016/03/18 00:01:57]

What if twistd.pid is never created?  Does master manager have its own timeout?

 
 ifeq ($(BUILDBOT_PATH),$(BUILDBOT8_PATH))
 start-prof: bootstrap
 else
 start-prof:
 endif
         TWISTD_PROFILE=1 PYTHONPATH=$(PYTHONPATH) python $(SCRIPTS_DIR)/common/twistd --no_save -y buildbot.tac
 
 stop: notify printstep
 ifndef NO_REVISION_AUDIT
@@ skipping 26 matching lines @@
 
 last-restart:
         @if `test -f twistd.pid`; then stat -c %y `readlink -f twistd.pid` | \
             cut -d "." -f1; fi;
         @ls -t -1 twistd.log* | while read f; do tac $$f | grep -m 1 \
             "Creating BuildMaster"; done | head -n 1
 
 wait:
         while `test -f twistd.pid`; do sleep 1; done;
 
+waitforstart:
+        while `test ! -f twistd.pid`; do sleep 1; done;
+
 restart: notify stop wait start log
 
 restart-prof: stop wait start-prof log
 
 # This target is only known to work on 0.8.x masters.
 upgrade: printstep
         @[ -e '.dbconfig' ] || [ -e 'state.sqlite' ] || \
         PYTHONPATH=$(PYTHONPATH) python buildbot upgrade-master .
 
 # This target is only known to be useful on 0.8.x masters.
 bootstrap: printstep
         @[ -e '.dbconfig' ] || [ -e 'state.sqlite' ] || \
         PYTHONPATH=$(PYTHONPATH) python $(SCRIPTS_DIR)/tools/state_create.py \
         --restore --db='state.sqlite' --txt '../state-template.txt'
 
 setup:
         @echo export PYTHONPATH=$(PYTHONPATH)