Check for permission errors in queues and defer queue initialization until use. Fixes #1897.

headphones/logger.py

@@ -24,6 +24,7 @@ import headphones
 import threading
 import traceback
 import logging
+import errno
 import sys
 import os
 
@@ -35,8 +36,8 @@ MAX_FILES = 5
 # Headphones logger
 logger = logging.getLogger("headphones")
 
-# Global queue of multiprocessing logging
-queue = multiprocessing.Queue()
+# Global queue for multiprocessing logging
+queue = None
 
 class LogListHandler(logging.Handler):
     """
@@ -56,13 +57,33 @@ def listener():
     To be used in a with statement in the main process, for multiprocessing.
     """
 
-    queue_listener = QueueListener(queue, *logger.handlers)
+    global queue
 
-    try:
-        queue_listener.start()
+    # Initialize queue if not already done
+    if queue is None:
+        try:
+            queue = multiprocessing.Queue()
+        except IOError as e:
+            queue = False
+
+            # Some machines don't have access to /dev/shm. See
+            # http://stackoverflow.com/questions/2009278 for more information.
+            if e.errno == errno.EACCES:
+                logger.warning("Multiprocess logging disabled, because "
+                    "current user cannot map shared memory. You won't see any" \
+                    "logging generated by the worker processed.")
+
+    # Multiprocess logging may be disabled.
+    if not queue:
         yield
-    finally:
-        queue_listener.stop()
+    else:
+        queue_listener = QueueListener(queue, *logger.handlers)
+
+        try:
+            queue_listener.start()
+            yield
+        finally:
+            queue_listener.stop()
 
 def initMultiprocessing():
     """
@@ -71,6 +92,11 @@ def initMultiprocessing():
     completely.
     """
 
+    # Multiprocess logging may be disabled.
+    if not queue:
+        return
+
+    # Remove all handlers and add the Queue handler as the only one.
     for handler in logger.handlers[:]:
         logger.removeHandler(handler)