Add ProcessMonitor class

docs/index.rst

@@ -8,19 +8,19 @@ Python Execution Contexts
 Introduction
 ------------
 
-``econtext`` is a library for building distributed self-replicating programs in
+``econtext`` is a library for writing distributed self-replicating programs in
 Python.
 
 There is no requirement for installing packages, copying files around, writing
-shell snippets, upfront configuration, or providing any secondary link to the
+shell snippets, upfront configuration, or providing any secondary link to a
 remote machine aside from an SSH connection. Due to its origins for use in
 managing potentially damaged infrastructure, the **remote machine need not even
 have free disk space or a writeable filesystem**.
 
 It is not intended as a generic RPC framework; the goal is to provide a robust
-and efficient low-level API on which tools like `Salt`_ or `Ansible`_ can be
-built, and while the API is quite friendly and similar in scope to `Fabric`_,
-ultimately it should not be used directly by consumer software.
+and efficient low-level API on which tools like `Salt`_, `Ansible`_, or
+`Fabric`_ can be built, and while the API is quite friendly and comparable to
+`Fabric`_, ultimately it is not intended for direct use by consumer software.
 
 .. _Salt: https://docs.saltstack.com/en/latest/
 .. _Ansible: http://docs.ansible.com/
@@ -43,10 +43,10 @@ with exotic connection methods such as WMI, `telnet`, or console-over-IPMI.
 
 .. warning::
 
-    econtext is alpha-quality software. If intend to you use it, you should be
-    aware how little real world testing it has received, the total absence of
-    any tests, and the nightmare-level difficulty of debugging hangs in a tree
-    of processes running identical code straddling multiple thread and machine
+    This is alpha-quality code. If you intend to use it, be aware of how little
+    real world testing it has received, the total absence of any systematic
+    tests, and the nightmare-level difficulty of debugging hangs in a tree of
+    processes running identical code straddling multiple thread and machine
     boundaries! ``router.enable_debug()`` is your friend.
 
     If you think you have a use for this software, please `drop me an e-mail`_

docs/internals.rst

@@ -50,6 +50,8 @@ ExternalContext Class
 econtext.master
 ===============
 
+.. autoclass:: econtext.master.ProcessMonitor
+
 
 Helper Functions
 ----------------

econtext/master.py

@@ -14,6 +14,7 @@ import os
 import pkgutil
 import re
 import select
+import signal
 import socket
 import sys
 import textwrap
@@ -612,3 +613,28 @@ class Router(econtext.core.Router):
 
         self._context_by_id[context.context_id] = context
         return context
+
+
+class ProcessMonitor(object):
+    def __init__(self):
+        # pid -> callback()
+        self.callback_by_pid = {}
+        signal.signal(signal.SIGCHLD, self._on_sigchld)
+
+    def _on_sigchld(self, _signum, _frame):
+        for pid, callback in self.callback_by_pid.items():
+            pid, status = os.waitpid(pid, os.WNOHANG)
+            if pid:
+                callback(status)
+                del self.callback_by_pid[pid]
+
+    def add(self, pid, callback):
+        self.callback_by_pid[pid] = callback
+
+    _instance = None
+
+    @classmethod
+    def instance(cls):
+        if cls._instance is None:
+            cls._instance = cls()
+        return cls._instance