ansible: stash PID files in CWD if requested for debugging.

ansible_mitogen/process.py

@@ -94,6 +94,24 @@ def getenv_int(key, default=0):
         return default
 
 
+def save_pid(name):
+    """
+    When debugging and profiling, it is very annoying to poke through the
+    process list to discover the currently running Ansible and MuxProcess IDs,
+    especially when trying to catch an issue during early startup. So here, if
+    a magic environment variable set, stash them in hidden files in the CWD::
+
+        alias muxpid="cat .ansible-mux.pid"
+        alias anspid="cat .ansible-controller.pid"
+
+        gdb -p $(muxpid)
+        perf top -p $(anspid)
+    """
+    if os.environ.get('MITOGEN_SAVE_PIDS'):
+        with open('.ansible-%s.pid' % (name,), 'w') as fp:
+            fp.write(str(os.getpid()))
+
+
 class MuxProcess(object):
     """
     Implement a subprocess forked from the Ansible top-level, as a safe place
@@ -173,11 +191,13 @@ class MuxProcess(object):
         if _init_logging:
             ansible_mitogen.logging.setup()
         if cls.child_pid:
+            save_pid('controller')
             ansible_mitogen.affinity.policy.assign_controller()
             cls.child_sock.close()
             cls.child_sock = None
             mitogen.core.io_op(cls.worker_sock.recv, 1)
         else:
+            save_pid('mux')
             ansible_mitogen.affinity.policy.assign_muxprocess()
             cls.worker_sock.close()
             cls.worker_sock = None