uWSGI postfork hooks (#207)

* Add uWSGI postfork hook support

* Immediate reset on fork and hook cleanup

* More refinements: add thread disabled warning

Author: pglombardo

instana/__init__.py

@@ -53,6 +53,7 @@ def boot_agent():
 
     import instana.singletons
 
+    # Instrumentation
     if "INSTANA_DISABLE_AUTO_INSTR" not in os.environ:
         # Import & initialize instrumentation
         if sys.version_info >= (3, 5, 3):
@@ -81,6 +82,8 @@ def boot_agent():
         from .instrumentation import urllib3
         from .instrumentation.django import middleware
 
+    # Hooks
+    from .hooks import hook_uwsgi
 
 if "INSTANA_MAGIC" in os.environ:
     pkg_resources.working_set.add_entry("/tmp/instana/python")

instana/agent.py

@@ -154,7 +154,7 @@ def announce(self, discovery):
         """
         try:
             url = self.__discovery_url()
-            logger.debug("making announce request to %s", url)
+            # logger.debug("making announce request to %s", url)
             response = None
             response = self.client.put(url,
                                        data=to_json(discovery),

instana/fsm.py

@@ -90,12 +90,8 @@ def reset(self):
 
         :return: void
         """
-        logger.debug("State machine being reset.  Will schedule new announce cycle 6 seconds from now.")
-
-        self.timer = t.Timer(6, self.fsm.lookup)
-        self.timer.daemon = True
-        self.timer.name = self.THREAD_NAME
-        self.timer.start()
+        logger.debug("State machine being reset.  Will start a new announce cycle.")
+        self.fsm.lookup()
 
     def lookup_agent_host(self, e):
         self.agent.should_threads_shutdown.clear()

instana/hooks/__init__.py

@@ -0,0 +1,38 @@
+"""
+The uwsgi and uwsgidecorators packages are added automatically to the Python environment
+when running under uWSGI.  Here we attempt to detect the presence of these packages and
+then use the appropriate hooks.
+"""
+from __future__ import absolute_import
+
+from ..log import logger
+from ..singletons import agent
+
+try:
+    import uwsgi
+    logger.debug("uWSGI options: %s", uwsgi.opt)
+
+    opt_master = uwsgi.opt.get('master', False)
+    opt_lazy_apps = uwsgi.opt.get('lazy-apps', False)
+
+    if uwsgi.opt.get('enable-threads', False) is False:
+        logger.warn("Required: uWSGI threads are not enabled.  " +
+                    "Please enable by using the uWSGI --enable-threads option.")
+
+    if opt_master and opt_lazy_apps is False:
+        # --master is supplied in uWSGI options (otherwise uwsgidecorators package won't be available)
+        # When --lazy-apps is True, this postfork hook isn't needed
+        import uwsgidecorators
+
+        @uwsgidecorators.postfork
+        def uwsgi_handle_fork():
+            """ This is our uWSGI hook to detect and act when worker processes are forked off. """
+            logger.debug("Handling uWSGI fork...")
+            agent.handle_fork()
+
+        logger.debug("Applied uWSGI hooks")
+    else:
+        logger.debug("uWSGI --master=%s --lazy-apps=%s: postfork hooks not applied", opt_master, opt_lazy_apps)
+except ImportError as e:
+    logger.debug('uwsgi hooks: decorators not available: %s', e)
+    pass