handle KeyboardInterrupts in pipeline.py

beets/util/pipeline.py

@@ -22,7 +22,13 @@ BUBBLE constant from any stage coroutine except the last.
 
 In the parallel case, the implementation transparently handles thread
 shutdown when the processing is complete and when a stage raises an
-exception.
+exception. KeyboardInterrupts (^C) are also handled.
+
+When running a parallel pipeline, it is also possible to use
+multiple coroutines for the same pipeline stage; this lets you speed
+up a bottleneck stage by dividing its work among multiple threads.
+To do so, pass an iterable of coroutines to the Pipeline constructor
+in place of any single coroutine.
 """
 from __future__ import with_statement # for Python 2.5
 import Queue
@@ -271,13 +277,24 @@ class Pipeline(object):
             thread.start()
         
         # Wait for termination. The final thread lasts the longest.
-        threads[-1].join()
+        try:
+            # Using a timeout allows us to receive KeyboardInterrupt
+            # exceptions during the join().
+            while threads[-1].isAlive():
+                threads[-1].join(1)
+
+        except:
+            # Stop all the threads immediately.
+            for thread in threads:
+                thread.abort()
+            raise
         
-        # Make completely sure that all the threads have finished
-        # before we return. They should already be either finished,
-        # in normal operation, or aborted, in case of an exception.
-        for thread in threads[:-1]:
-            thread.join()
+        finally:
+            # Make completely sure that all the threads have finished
+            # before we return. They should already be either finished,
+            # in normal operation, or aborted, in case of an exception.
+            for thread in threads[:-1]:
+                thread.join()
 
         for thread in threads:
             exc_info = thread.exc_info