Writing PID file whenever Flamenco-Worker is running.

Added optional creation and removal of a PID file. This only happens when
the `pid` configuration option is given, pointing to the location of the
PID file.

This is an attempt to prevent the sysv script from starting Flamenco-Worker
when it is already running (i.e. after two "service flamenco-worker start"
commands).

CHANGELOG.md

@@ -4,6 +4,12 @@ This file logs the changes that are actually interesting to users (new features,
 changed functionality, fixed bugs).
 
 
+## Version 2.0.3 (under development)
+
+- Added optional creation and removal of a PID file. This only happens when the `pid`
+  configuration option is given, pointing to the location of the PID file.
+
+
 ## Version 2.0.2 (released 2017-04-07)
 
 - Added support for task types. Workers only get tasks of the types they support.

README.md

@@ -36,6 +36,11 @@ config files.
 - `job_types`: Space-separated list of job types this worker may execute.
 - `task_update_queue_db`: filename of the SQLite3 database holding the queue of task
   updates to be sent to the Master.
+- `pid`: Location of the PID file that'll be created when Flamenco-Worker is running,
+  and removed on startup. It'll contain the process ID. This is required when using the
+  SysV service script. When not present (or with empty value), the PID file will neither
+  be created nor removed.
+
 These configuration keys are also required, but are created automatically upon startup
 when they don't exist yet:
 

flamenco-worker.cfg

 [flamenco-worker]
+# Uncomment to create a PID file at the configured location.
+# pid = /var/run/flamenco-worker/flamenco-worker.pid
 manager_url = http://localhost:8083/
 task_types = sleep blender-render file-management
 task_update_queue_db = flamenco-worker.db

flamenco_worker/cli.py

@@ -4,10 +4,36 @@ import argparse
 import asyncio
 import logging
 import logging.config
+import pathlib
 
 import requests
 
 
+def create_pidfile(path: pathlib.Path):
+    """Creates a PID file in the given location.
+
+    Als uses the atexit module to remove the PID file once the process is terminated.
+    """
+
+    import atexit
+    import os
+
+    def remove_pidfile():
+        if path.exists():
+            path.unlink()
+
+    atexit.register(remove_pidfile)
+
+    log = logging.getLogger(__name__)
+    pid = os.getpid()
+
+    if path.exists():
+        log.info('Overwriting PID file %s with our PID %i', path, pid)
+    else:
+        log.info('Creating PID file %s with our PID %i', path, pid)
+    path.write_text(str(pid), encoding='ascii')
+
+
 def main():
     parser = argparse.ArgumentParser()
     parser.add_argument('-c', '--config',
@@ -25,6 +51,13 @@ def main():
     log = logging.getLogger(__name__)
     log.debug('Starting')
 
+    # Create the PID file, if the location is configured.
+    pidfile = confparser.value('pid')
+    if pidfile:
+        create_pidfile(pathlib.Path(pidfile))
+    else:
+        log.info("Not creating PID file because the configuration has no value for the 'pid' key.")
+
     # Patch AsyncIO
     from . import patch_asyncio
     patch_asyncio.patch_asyncio()

flamenco_worker/config.py

@@ -14,6 +14,7 @@ CONFIG_SECTION = 'flamenco-worker'
 
 DEFAULT_CONFIG = {
     'flamenco-worker': collections.OrderedDict([
+        ('pid', ''),  # Optional location of the PID-file
         ('manager_url', 'http://flamenco-manager/'),
         ('task_types', 'unknown sleep blender-render'),
         ('task_update_queue_db', 'flamenco-worker.db'),

system-integration/sysv/flamenco-worker

@@ -21,7 +21,7 @@ DESC="Flamenco Worker"
 NAME=flamenco-worker
 DAEMON=$FLAMENCO_WORKER
 SCRIPTNAME=/etc/init.d/$NAME
-PIDFILE=/var/run/$NAME.pid
+PIDFILE=/home/guest/local-flamenco-worker/$NAME.pid
 USER=guest
 GROUP=guest
 
@@ -38,7 +38,7 @@ do_start()
 {
     sudo -u $USER mkdir -p /home/guest/local-flamenco-worker
     start-stop-daemon --start --quiet --pidfile $PIDFILE --name $NAME \
-        --exec $DAEMON --chuid $USER:$GROUP --chdir $WORK_DIR --make-pidfile --background
+        --exec $DAEMON --chuid $USER:$GROUP --chdir $WORK_DIR --background
     return "$?"
 }