[enh] Add a non-blocking stream reader class to helpers

moulinette/helpers.py

@@ -1,2 +1,55 @@
 # -*- coding: utf-8 -*-
 
+from threading import Thread
+from Queue import Queue, Empty
+
+class NonBlockingStreamReader:
+    """A non-blocking stream reader
+
+    Open a separate thread which reads lines from the stream whenever data
+    becomes available and stores the data in a queue.
+
+    Based on: http://eyalarubas.com/python-subproc-nonblock.html
+
+    Keyword arguments:
+        - stream -- The stream to read from
+
+    """
+    def __init__(self, stream):
+        self._s = stream
+        self._q = Queue()
+
+        def _populateQueue(stream, queue):
+            """Collect lines from the stream and put them in the queue"""
+            while True:
+                line = stream.readline()
+                if line:
+                    queue.put(line)
+                else:
+                    break
+
+        self._t = Thread(target=_populateQueue, args=(self._s, self._q))
+        self._t.daemon = True
+        # Start collecting lines from the stream
+        self._t.start()
+
+    def readline(self, block=False, timeout=None):
+        """Read line from the stream
+
+        Attempt to pull from the queue the data and return it. If no data is
+        available or timeout has expired, it returns None.
+
+        Keyword arguments:
+            - block -- If True, block if necessary until data is available
+            - timeout -- The number of seconds to block
+
+        """
+        try:
+            return self._q.get(block=timeout is not None,
+                    timeout=timeout)
+        except Empty:
+            return None
+
+    def close(self):
+        """Close the stream"""
+        self._s.close()