Allocators: allow zero size, return None

doc/tools.rst

@@ -54,6 +54,11 @@ not complicated::
 
         Allocate a :class:`pyopencl.Buffer` of the given *size*.
 
+        .. versionchanged :: 2020.2
+
+            The allocator will succeed even for allocations of size zero,
+            returning *None*.
+
 .. class:: ImmediateAllocator(queue, mem_flags=pyopencl.mem_flags.READ_WRITE)
 
     *mem_flags* takes its values from :class:`pyopencl.mem_flags` and corresponds
@@ -68,6 +73,11 @@ not complicated::
 
         Allocate a :class:`pyopencl.Buffer` of the given *size*.
 
+        .. versionchanged :: 2020.2
+
+            The allocator will succeed even for allocations of size zero,
+            returning *None*.
+
 .. class:: MemoryPool(allocator[, leading_bits_in_bin_id])
 
     A memory pool for OpenCL device memory. *allocator* must be an instance of

src/wrap_mempool.cpp

@@ -104,6 +104,9 @@ namespace
 
       pointer_type allocate(size_type s)
       {
+        if (s == 0)
+          return nullptr;
+
         return pyopencl::create_buffer(m_context->data(), m_flags, s, 0);
       }
   };
@@ -137,6 +140,9 @@ namespace
 
       pointer_type allocate(size_type s)
       {
+        if (s == 0)
+          return nullptr;
+
         pointer_type ptr =  pyopencl::create_buffer(
             m_context->data(), m_flags, s, 0);