Disable GCCollector in multiprocess mode (#324)

* Add Pytest cache and Coverage HTML report dirs to gitignore
* Disable the GC collector in multiprocess mode

Works around #322

Signed-off-by: Aarni Koskela <akx@iki.fi>

Author: akx

.gitignore

@@ -6,3 +6,5 @@ dist
 .coverage.*
 .coverage
 .tox
+.*cache
+htmlcov

prometheus_client/gc_collector.py

@@ -3,13 +3,20 @@
 from __future__ import unicode_literals
 
 import gc
+import os
 import time
 
 from . import core
 
 class GCCollector(object):
     """Collector for Garbage collection statistics."""
     def __init__(self, registry=core.REGISTRY, gc=gc):
+        # To work around the deadlock issue described in
+        # https://github.com/prometheus/client_python/issues/322,
+        # the GC collector is always disabled in multiprocess mode.
+        if 'prometheus_multiproc_dir' in os.environ:
+            return
+
         if not hasattr(gc, 'callbacks'):
             return