21639: Don't try to madvise zero length blocks

Arvados-DCO-1.1-Signed-off-by: Peter Amstutz <peter.amstutz@curii.com>

diff --git a/sdk/python/arvados/diskcache.py b/sdk/python/arvados/diskcache.py
index 3749298210c3b87a5b2b89ec90d53f469c65a92f..2d85c1126623af9974ce892a79dcb5fc5472ce69 100644 (file)
--- a/sdk/python/arvados/diskcache.py
+++ b/sdk/python/arvados/diskcache.py
@@ -32,7 +32,7 @@ class DiskCacheSlot(object):
 
     def get(self):
         self.ready.wait()
-        if self.content is not None:
+        if self.content is not None and len(self.content) > 0:
             self.content.madvise(mmap.MADV_WILLNEED)
         return self.content