EventLoop.child_watch_add: dynamic IO watch

The IO watch is dynamically registered and unregistered as needed,
since we don't want to consider it as a valid source of events when
there are no child listeners. It's important to distinguish when there
are no valid sources of IO events, in order to avoid an endless poll
call if there's no timeout. This fixes possbible endless poll calls
since commit 1979a6cdfcd8c6bae4565982d82d862be07ba5be.

diff --git a/pym/portage/util/_eventloop/EventLoop.py b/pym/portage/util/_eventloop/EventLoop.py
index e38134258c3c9d6dc988b76a53bd2d5ed050842a..7f171fb8c77310b8232601d181143a1d1636a981 100644 (file)
--- a/pym/portage/util/_eventloop/EventLoop.py
+++ b/pym/portage/util/_eventloop/EventLoop.py
@@ -57,6 +57,7 @@ class EventLoop(object):
                self._child_handlers = {}
                self._sigchld_read = None
                self._sigchld_write = None
+               self._sigchld_src_id = None
                self._pid = os.getpid()
 
        def _poll(self, timeout=None):
@@ -246,19 +247,26 @@ class EventLoop(object):
                source_id = self._event_handler_id
                self._child_handlers[source_id] = self._child_callback_class(
                        callback=callback, data=data, pid=pid, source_id=source_id)
+
                if self._sigchld_read is None:
-                       self._sigchld_init()
+                       self._sigchld_read, self._sigchld_write = os.pipe()
+                       fcntl.fcntl(self._sigchld_read, fcntl.F_SETFL,
+                               fcntl.fcntl(self._sigchld_read, fcntl.F_GETFL) | os.O_NONBLOCK)
+
+               # The IO watch is dynamically registered and unregistered as
+               # needed, since we don't want to consider it as a valid source
+               # of events when there are no child listeners. It's important
+               # to distinguish when there are no valid sources of IO events,
+               # in order to avoid an endless poll call if there's no timeout.
+               if self._sigchld_src_id is None:
+                       self._sigchld_src_id = self.io_add_watch(
+                               self._sigchld_read, self.IO_IN, self._sigchld_io_cb)
+                       signal.signal(signal.SIGCHLD, self._sigchld_sig_cb)
+
                # poll now, in case the SIGCHLD has already arrived
                self._poll_child_processes()
                return source_id
 
-       def _sigchld_init(self):
-               self._sigchld_read, self._sigchld_write = os.pipe()
-               fcntl.fcntl(self._sigchld_read, fcntl.F_SETFL,
-                       fcntl.fcntl(self._sigchld_read, fcntl.F_GETFL) | os.O_NONBLOCK)
-               self.io_add_watch(self._sigchld_read, self.IO_IN, self._sigchld_io_cb)
-               signal.signal(signal.SIGCHLD, self._sigchld_sig_cb)
-
        def _sigchld_sig_cb(self, signum, frame):
                # If this signal handler was not installed by the
                # current process then the signal doesn't belong to
@@ -292,14 +300,14 @@ class EventLoop(object):
                                if e.errno != errno.ECHILD:
                                        raise
                                del e
-                               self._child_handlers.pop(x.source_id, None)
+                               self.source_remove(x.source_id)
                        else:
                                # With waitpid and WNOHANG, only check the
                                # first element of the tuple since the second
                                # element may vary (bug #337465).
                                if wait_retval[0] != 0:
                                        calls += 1
-                                       self._child_handlers.pop(x.source_id, None)
+                                       self.source_remove(x.source_id)
                                        x.callback(x.pid, wait_retval[1], x.data)
 
                return bool(calls)
@@ -429,6 +437,10 @@ class EventLoop(object):
                """
                x = self._child_handlers.pop(reg_id, None)
                if x is not None:
+                       if not self._child_handlers:
+                               signal.signal(signal.SIGCHLD, signal.SIG_DFL)
+                               self.source_remove(self._sigchld_src_id)
+                               self._sigchld_src_id = None
                        return True
                idle_callback = self._idle_callbacks.pop(reg_id, None)
                if idle_callback is not None: