posix: fix PosixPollSerial with timeout=None and add cancel support

fixes pyserial#265

Author: zsquareplusc

serial/serialposix.py

@@ -733,21 +733,28 @@ def read(self, size=1):
         if not self.is_open:
             raise portNotOpenError
         read = bytearray()
+        timeout = Timeout(self._timeout)
         poll = select.poll()
         poll.register(self.fd, select.POLLIN | select.POLLERR | select.POLLHUP | select.POLLNVAL)
+        poll.register(self.pipe_abort_read_r, select.POLLIN | select.POLLERR | select.POLLHUP | select.POLLNVAL)
         if size > 0:
             while len(read) < size:
                 # print "\tread(): size",size, "have", len(read)    #debug
                 # wait until device becomes ready to read (or something fails)
-                for fd, event in poll.poll(self._timeout * 1000):
+                for fd, event in poll.poll(None if timeout.is_infinite else (timeout.time_left() * 1000)):
+                    if fd == self.pipe_abort_read_r:
+                        break
                     if event & (select.POLLERR | select.POLLHUP | select.POLLNVAL):
                         raise SerialException('device reports error (poll)')
                     #  we don't care if it is select.POLLIN or timeout, that's
                     #  handled below
+                if fd == self.pipe_abort_read_r:
+                    os.read(self.pipe_abort_read_r, 1000)
+                    break
                 buf = os.read(self.fd, size - len(read))
                 read.extend(buf)
-                if ((self._timeout is not None and self._timeout >= 0) or
-                        (self._inter_byte_timeout is not None and self._inter_byte_timeout > 0)) and not buf:
+                if timeout.expired() \
+                        or (self._inter_byte_timeout is not None and self._inter_byte_timeout > 0) and not buf:
                     break   # early abort on timeout
         return bytes(read)