Add Process and Signals support

Signed-off-by: Jan Lindemann <jan@janware.com>

tools/python/jwutils/Process.py

@@ -0,0 +1,68 @@
+from abc import ABC, abstractmethod
+from enum import Enum, Flag, auto
+
+def _sigchld_handler(signum, process):
+    if not signum == signal.SIGCHLD:
+        return
+    Process.propagate_signal(signum)
+
+class Process(ABC): # export
+
+    __processes                   = []
+
+    class State(Enum):
+        Running                   = auto()
+        Shutdown                  = auto()
+        Done                      = auto()
+
+    class Flags(Flag):
+        FailOnExitWithoutShutdown = auto()
+
+    def __init__(self):
+        self.__state = Running
+        self.__flags = Flags.FailOnExitWithoutShutdown
+        if len(self.__processes) == 0:
+            self._signals().add_handler(signals.SIGCHLD, _sigchld_handler)
+        self.__processes.add(self)
+
+    @classmethod
+    def propagate_signal(cls, signum):
+        for p in cls.__processes:
+            p.__signal(signum)
+
+    def signal(self, signum):
+        if signum == signals.SIGCHLD:
+            self.exited()
+
+    @abstractmethod
+    def _pid(self):
+        pass
+
+    @classmethod
+    @abstractmethod
+    def signals(cls):
+        pass
+
+    # to be reimplemented
+    def _request_shutdown(self):
+        pass
+
+    # to be reimplemented
+    def name(self):
+        return str(self._pid())
+
+    def request_shutdown(self):
+        if not self.__state == Shutdown:
+            self.__state = Shutdown
+            self._request_shutdown()
+
+    def exited(self):
+        if self.__state == Process.State.Running:
+            slog(ERR, 'process "{}" exited unexpectedly'.format(process.name()))
+            if __flags & Process.Flags.FailOnExitWithoutShutdown:
+                slog(ERR, 'exiting')
+                exit(1)
+        self.__state = Process.State.Done
+        self.__processes.erase(self)
+        if len(self.__processes) == 0:
+            self._signals().remove_handler(signals.SIGCHLD) # FIXME: broken logic