[BUG] Not all global static references are __attribute__((visibility(default)))

[wence-]

Describe the bug

In #826, it was noted that the std::map in per_device_resource.hpp is a global static reference returned from an inline function. This causes issues with the RMM-default visibility(hidden) attribute of functions in the RMM headers, since although when compiling within a single library, the linker will uniquify the references to the function, when RMM is included in two separate libraries, this does not occur.

As a consequence, with visibility(hidden), the static reference will be unique per library, but differ across libraries.

#833 fixed this for the particular case of rmm::mr::detail::get_map, by making that function RMM_EXPORT.

However, there are other static references returned from inline functions in that file that were not exported. These should also be RMM_EXPORT.

In particular rmm::mr::detail::map_lock returns a static reference to a mutex that protects accesses to the per-device-resource map. However, since it is visibility(hidden), we actually don't have a single map lock, and so we are actually not protecting concurrent access to the per-device-resource map from different libraries.

An example, printing the address of the map lock:

index a56a784a..d5afafe4 100644
--- a/include/rmm/mr/device/per_device_resource.hpp
+++ b/include/rmm/mr/device/per_device_resource.hpp
@@ -108,6 +108,7 @@ inline device_memory_resource* initial_resource()
 inline std::mutex& map_lock()
 {
   static std::mutex map_lock;
+  std::cout << "Map lock " << &map_lock << std::endl; 
   return map_lock;
 }

We see, when cudf is compiled and used from cudf python (the python bindings build a separate library that includes RMM):

import cudf
s = cudf.Series([1])

prints

Map lock 0x7355ec744e20
Map lock 0x7355bc40c400