Using Thrust Functions with raw pointers: Controlling the allocation of memory

Question

I have a question regarding the thrust library when using CUDA. I am using a thrust function, i.e. exclusive_scan, and I want to use raw pointers. I am using raw (device) pointers because I want to have full control of when the memory is allocated and deallocated.

After the function call, I will hand over the pointer to another data structure and then free the memory in either the destructor of this data structure, or in the next function call, when I recompute my (device) pointers. I came across for example this problem here now, which recommends to wrap the data structure in a device_vector. But then I run into the problem that the memory is freed once my device_vector goes out of scope, which I do not want. Having the device pointer globally is also not an option, since I am hacking code, i.e. it is used as a buffer and I would have to rewrite a lot if I wanted to do something like that.

Does anyone have a good workaround regarding this? The only chance I do see right now is to rewrite the thrust-function on my own, only using raw device-pointers.

EDIT: I misread, I can wrap it in a device_ptr instead of a device_vector. Asking further though, how could I solve this if there wasn't the option of using a device_ptr?

The question you linked to recommends wrapping in a device_ptr, not a device_vector. — talonmies
– talonmies, Commented Dec 10, 2019 at 10:34
Ah, you are right. I did oversee that detail, thank you. That leaves me with the question still however how I could do my memory management if I would not have this option. Should I open a new question for this? — RBaumgar
– RBaumgar, Commented Dec 10, 2019 at 10:53

Johan · Accepted Answer · 2019-12-11 11:57:46Z

4

There is no problem using plain pointers in thrust methods.

For data on the device do:

....
struct DoSomething {
    __device__ int operator()(int item) { return 1; }
};

int* IntData;
cudaMalloc(&IntData, sizeof(int) * count);
auto dev_data = device_pointer_cast(IntData);
thrust::generate(dev_data, dev_data + count, DoSomething());
thrust::sort(dev_data, dev_data + count);
....
cudaFree(IntData);

For data on the host use plain malloc/free and raw_pointer_cast instead of device_pointer_cast. See: thrust: Memory management

answered Dec 11, 2019 at 11:57

Johan

77.4k28 gold badges204 silver badges346 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

talonmies Over a year ago

Technically that isn't using plain pointers. Plain pointer support would involve the dispatch policy versions of the thrust APIs

Collectives™ on Stack Overflow

Using Thrust Functions with raw pointers: Controlling the allocation of memory

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related