Flock master startup.

masters/master-common-rules.mk

Index: masters/master-common-rules.mk
diff --git a/masters/master-common-rules.mk b/masters/master-common-rules.mk
index a8b72e654c4b338ef119c8dca7894b33327c6d67..62758e352b92564267e03dabd10aaf6c926c9a0f 100644
--- a/masters/master-common-rules.mk
+++ b/masters/master-common-rules.mk
@@ -25,6 +25,12 @@ INFRA_RUNPY = /opt/infra-python/run.py
 SHORT_HOSTNAME := $(shell hostname -s)
 CURRENT_DIR = $(shell pwd)
 
+# Where we expect flock to live.
+FLOCK = /usr/bin/flock
+
+# Per-master lockfile.
+LOCKFILE = master_start.lock
+
 printstep:
 ifndef NO_REVISION_AUDIT
 	@echo "**  `python -c 'import datetime; print datetime.datetime.utcnow().isoformat() + "Z"'`	make $(MAKECMDGOALS)" >> actions.log
@@ -63,15 +69,14 @@ ifndef NO_REVISION_AUDIT
    || echo 'Running send_monitoring_event failed, skipping sending events.' \
   ) 2>&1 | tee -a actions.log
 endif
-	# There is a race condition between startup and when twistd.pid is written.
-	# Anyone issuing a second `make start` before the twistd.pid is written will
-	# spawn two masters. This is hopefully unlikely, but a proper solution would
-	# be to use flock (not available on OSX). The critical section contains BOTH
-	# the twistd start and the wait for the twistd.pid.
-	@echo 'Now running Buildbot master.'
-	PYTHONPATH=$(PYTHONPATH) python $(SCRIPTS_DIR)/common/twistd --no_save -y buildbot.tac
-	@echo 'Waiting for creation of twistd.pid...'
-	while `test ! -f twistd.pid`; do sleep 1; done;
+ifneq ($(wildcard $(FLOCK)),)
+	PYTHONPATH=$(PYTHONPATH) SCRIPTS_DIR=$(SCRIPTS_DIR) $(FLOCK) -n $(LOCKFILE) $(TOPLEVEL_DIR)/masters/start_master.sh || ( \
+	echo "Failure to start master. Check to see if a master is running and" \
+	     "holding the lock on $(LOCKFILE)."; exit 1)
+else
+	PYTHONPATH=$(PYTHONPATH) SCRIPTS_DIR=$(SCRIPTS_DIR) $(TOPLEVEL_DIR)/masters/start_master.sh
+endif
+
 
 ifeq ($(BUILDBOT_PATH),$(BUILDBOT8_PATH))
 start-prof: bootstrap