Unify service stop sequence

We still had some variations in how services stop.  Finger, merger,
and scheduler all used signal.pause in a while loop which is
incompatible with stopping via the command socket (since we would
always restart the pause).  Sending these components a stop or
graceful signal would cause them to wait forever.

Instead of using signal.pause, use the thread.join methods within
a while loop, and if we encounter a KeyboardInterrupt (C-c) during
the join, call our exit handler and retry the join loop.

This maintains the intent of the signal.pause loop (which is to
make C-c exit cleanly) while also being compatible with an internal
stop issued via the command socket.

The stop sequence is now unified across all components.  The executor
has an additional complication in that it forks a process to handle
streaming.  To keep a C-c shutdown clean, we also handle a keyboard
interrupt in the child process and use it to indicate the start of
a shutdown.  In the main executor process, we now close the socket
which is used to keep the child running and then wait for the child
to exit before the main process exits (so that the child doesn't
keep running and emit a log line after the parent returns control
to the terminal).

Change-Id: I216b76d6aaf7ebd01fa8cca843f03fd7a3eea16d

zuul/cmd/executor.py

@@ -67,12 +67,16 @@ class Executor(zuul.cmd.ZuulDaemonApp):
 
             # Keep running until the parent dies:
             pipe_read = os.fdopen(pipe_read)
-            pipe_read.read()
+            try:
+                pipe_read.read()
+            except KeyboardInterrupt:
+                pass
             self.log.info("Stopping log streamer")
             streamer.stop()
             os._exit(0)
         else:
             os.close(pipe_read)
+            self.log_streamer_pipe = pipe_write
             self.log_streamer_pid = child_pid
 
     def run(self):
@@ -113,7 +117,16 @@ class Executor(zuul.cmd.ZuulDaemonApp):
         if self.args.nodaemon:
             signal.signal(signal.SIGTERM, self.exit_handler)
 
-        self.executor.join()
+        while True:
+            try:
+                self.executor.join()
+                break
+            except KeyboardInterrupt:
+                print("Ctrl + C: asking executor to exit nicely...\n")
+                self.exit_handler(signal.SIGINT, None)
+
+        os.close(self.log_streamer_pipe)
+        os.waitpid(self.log_streamer_pid, 0)
 
 
 def main():

zuul/cmd/fingergw.py

@@ -38,6 +38,10 @@ class FingerGatewayApp(zuul.cmd.ZuulDaemonApp):
         self.addSubCommands(parser, fingergw.COMMANDS)
         return parser
 
+    def exit_handler(self, signum, frame):
+        if self.gateway:
+            self.gateway.stop()
+
     def run(self):
         '''
         Main entry point for the FingerGatewayApp.
@@ -59,28 +63,18 @@ class FingerGatewayApp(zuul.cmd.ZuulDaemonApp):
             self.getPidFile(),
         )
 
-        self.log.info('Starting Zuul finger gateway app')
         self.gateway.start()
 
         if self.args.nodaemon:
-            # NOTE(Shrews): When running in non-daemon mode, although sending
-            # the 'stop' command via the command socket will shutdown the
-            # gateway, it's still necessary to Ctrl+C to stop the app.
-            while True:
-                try:
-                    signal.pause()
-                except KeyboardInterrupt:
-                    print("Ctrl + C: asking gateway to exit nicely...\n")
-                    self.stop()
-                    break
-        else:
-            self.gateway.wait()
+            signal.signal(signal.SIGTERM, self.exit_handler)
 
-        self.log.info('Stopped Zuul finger gateway app')
-
-    def stop(self):
-        if self.gateway:
-            self.gateway.stop()
+        while True:
+            try:
+                self.gateway.join()
+                break
+            except KeyboardInterrupt:
+                print("Ctrl + C: asking gateway to exit nicely...\n")
+                self.exit_handler(signal.SIGINT, None)
 
 
 def main():

zuul/cmd/merger.py

@@ -49,19 +49,15 @@ class Merger(zuul.cmd.ZuulDaemonApp):
 
         if self.args.nodaemon:
             signal.signal(signal.SIGTERM, self.exit_handler)
-            while True:
-                try:
-                    signal.pause()
-                except KeyboardInterrupt:
-                    print("Ctrl + C: asking merger to exit nicely...\n")
-                    self.exit_handler(signal.SIGINT, None)
-        else:
-            self.merger.join()
+
+        while True:
+            try:
+                self.merger.join()
+                break
+            except KeyboardInterrupt:
+                print("Ctrl + C: asking merger to exit nicely...\n")
+                self.exit_handler(signal.SIGINT, None)
 
 
 def main():
     Merger().main()
-
-
-if __name__ == "__main__":
-    main()

zuul/cmd/scheduler.py

@@ -109,14 +109,14 @@ class Scheduler(zuul.cmd.ZuulDaemonApp):
 
         if self.args.nodaemon:
             signal.signal(signal.SIGTERM, self.exit_handler)
-            while True:
-                try:
-                    signal.pause()
-                except KeyboardInterrupt:
-                    print("Ctrl + C: asking scheduler to exit nicely...\n")
-                    self.exit_handler(signal.SIGINT, None)
-        else:
-            self.sched.join()
+
+        while True:
+            try:
+                self.sched.join()
+                break
+            except KeyboardInterrupt:
+                print("Ctrl + C: asking scheduler to exit nicely...\n")
+                self.exit_handler(signal.SIGINT, None)
 
 
 def main():

zuul/lib/fingergw.py

@@ -217,6 +217,7 @@ class FingerGateway(object):
             raise
 
     def start(self):
+        self.log.info("Starting finger gateway")
         kwargs = dict(
             user=self.user,
             pid_file=self.pid_file,
@@ -260,6 +261,7 @@ class FingerGateway(object):
         self.log.info("Finger gateway is started")
 
     def stop(self):
+        self.log.info("Stopping finger gateway")
         self.component_info.state = self.component_info.STOPPED
 
         if self.server:
@@ -283,7 +285,7 @@ class FingerGateway(object):
 
         self.log.info("Finger gateway is stopped")
 
-    def wait(self):
+    def join(self):
         '''
         Wait on the gateway to shutdown.
         '''