Fix init race condition

zoe-scheduler.py

@@ -40,7 +40,8 @@ def main():
 
     tm = PeriodicTaskManager()
 
-    zoe_sched.init_tasks(tm)
+    barrier = zoe_sched.init_tasks(tm)
+    barrier.wait()  # wait for all tasks to be ready and running
 
     ipc_server.start_thread()
 

zoe_scheduler/periodic_tasks.py

@@ -13,18 +13,22 @@ class PeriodicTaskManager:
         self.terminate = Event()
         self.terminate.clear()
 
-    def add_task(self, name, func, delay):
-        th = Thread(name=name, target=self._generic_task, args=(name, delay, func))
+    def add_task(self, name, func, delay, ready_barrier):
+        th = Thread(name=name, target=self._generic_task, args=(name, delay, func, ready_barrier))
         th.daemon = True
         th.start()
 
-    def _generic_task(self, name, delay, func):
+    def _generic_task(self, name, delay, func, ready_barrier):
         log.info("Task {} started".format(name))
+        init_done = False
         while True:
             try:
                 func()
             except:
                 log.exception("Task {} raised an exception".format(name))
+            if not init_done:
+                init_done = True
+                ready_barrier.wait()
             stop = self.terminate.wait(delay)
             if stop:
                 break

zoe_scheduler/scheduler.py

 import logging
+from threading import Barrier
 import time
 
 from zoe_scheduler.platform import PlatformManager
@@ -73,10 +74,12 @@ class ZoeScheduler:
         self.platform_status = PlatformStatus(self)
         self.scheduler_policy = SimpleSchedulerPolicy(self.platform_status)
 
-    def init_tasks(self, tm: PeriodicTaskManager):
-        tm.add_task("platform status updater", self.platform_status.update, zoeconf.interval_status_refresh)
-        tm.add_task("proxy access timestamp updater", pm.update_proxy_access_timestamps, zoeconf.interval_proxy_update_accesses)
-        tm.add_task("execution health checker", self.platform.check_executions_health, zoeconf.interval_check_health)
+    def init_tasks(self, tm: PeriodicTaskManager) -> Barrier:
+        barrier = Barrier(4)  # number of tasks + main thread
+        tm.add_task("platform status updater", self.platform_status.update, zoeconf.interval_status_refresh, barrier)
+        tm.add_task("proxy access timestamp updater", pm.update_proxy_access_timestamps, zoeconf.interval_proxy_update_accesses, barrier)
+        tm.add_task("execution health checker", self.platform.check_executions_health, zoeconf.interval_check_health, barrier)
+        return barrier
 
     def incoming(self, execution: ExecutionState) -> bool:
         if not self.scheduler_policy.admission_control(execution.application.required_resources):

zoe_web/api/__init__.py

@@ -5,7 +5,6 @@ from flask import Blueprint, jsonify, request, session, abort, send_file
 
 from zoe_client import ZoeClient
 from common.configuration import ipcconf
-from common.exceptions import ApplicationStillRunning
 
 api_bp = Blueprint('api', __name__)
 
@@ -70,9 +69,7 @@ def application_delete(app_id):
     client = ZoeClient(ipcconf['server'], ipcconf['port'])
     _api_check_user(client)
 
-    try:
-        client.application_remove(app_id)
-    except ApplicationStillRunning:
+    if client.application_remove(app_id, False):
         return jsonify(status="error", msg="The application has active executions and cannot be deleted")
     else:
         return jsonify(status="ok")

zoe_web/web/start.py

@@ -4,7 +4,7 @@ from zoe_client import ZoeClient
 from common.configuration import ipcconf
 from zoe_web.web import web_bp
 import zoe_web.utils as web_utils
-from common.state.execution import Execution
+from zoe_client.entities import Execution
 
 
 @web_bp.route('/')