From 8e4d2c2f64a7a40faaf2a8e7bd73247d744ba9fb Mon Sep 17 00:00:00 2001
From: Andreas Kloeckner <inform@tiker.net>
Date: Sun, 21 Jun 2020 00:23:14 -0500
Subject: [PATCH] Adapt to no events being available for zero-size array
 allocations

---
 boxtree/tree_build.py | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/boxtree/tree_build.py b/boxtree/tree_build.py
index 8f652aa..38c69b7 100644
--- a/boxtree/tree_build.py
+++ b/boxtree/tree_build.py
@@ -220,7 +220,16 @@ class TreeBuilder(object):
 
         def zeros(shape, dtype):
             result = cl.array.zeros(queue, shape, dtype, allocator=allocator)
-            event, = result.events
+            if result.events:
+                event, = result.events
+            else:
+                from numbers import Number
+                if isinstance(shape, Number):
+                    shape = (shape,)
+                from pytools import product
+                assert product(shape) == 0
+                event = cl.enqueue_marker(queue)
+
             return result, event
 
         knl_info = self.get_kernel_info(dimensions, coord_dtype,
-- 
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