C API: Resources

Each computer system will have a number of distinct places in which the system will allow you to allocate memory. In Umpire’s world, these are memory resources. A memory resource can correspond to a hardware resource, but can also be used to identify memory with a particular characteristic, like “pinned” memory in a GPU system.

When you configure Umpire, it will create umpire::resource::MemoryResource s according to what is available on the system you are building for. For each resource, Umpire will create a default umpire_allocator that you can use. In the previous example, we were actually using an umpire_allocator created for the memory resource corresponding to the CPU memory.

The easiest way to identify resources is by name. The “HOST” resource is always available. In a system configured with NVIDIA GPUs, we also have resources that represent global GPU memory (“DEVICE”), unified memory that can be accessed by the CPU or GPU (“UM”) and host memory that can be accessed by the GPU (“PINNED”);

Umpire will create an umpire_allocator for each of these resources, and you can get them using the same umpire_resourcemanager_get_allocator_by_name call you saw in the previous example:

Note that every allocator supports the same calls, no matter which resource it is for, this means we can run the same code for all the resources available in the system:

As you can see, we can call this function with any valid resource name:

In the next example, we will learn how to move data between resources using operations.