cuda - error: class "cooperative_groups::__v1::thread_block" has no member "is_valid"

Question

We are trying to use some of the cooperative groups features in CUDA to write a small application. We are using Tesla V100 card with CUDA 11.0. But on using is_valid() method in thread_block the below error is observed:

error: class "cooperative_groups::__v1::thread_block" has no member "is_valid"

In the CUDA provided sample simpleCooperativeGroups.cu, in the kernel cgkernel() when the is_valid method is used, this error can be seen. The code snippet from the modified sample looks as below.

__global__ void cgkernel(){


// threadBlockGroup includes all threads in the block
thread_block threadBlockGroup = this_thread_block();
int threadBlockGroupSize=threadBlockGroup.size();

// workspace array in shared memory required for reduction
extern __shared__ int workspace[];

int input, output, expectedOutput;

// input to reduction, for each thread, is its' rank in the group
input=threadBlockGroup.thread_rank();

// expected output from analytical formula (n-1)(n)/2
// (noting that indexing starts at 0 rather than 1)
expectedOutput=(threadBlockGroupSize-1)*threadBlockGroupSize/2;

// perform reduction
output=sumReduction(threadBlockGroup, workspace, input);

bool valid = threadBlockGroup.is_valid();
.
.
.
}

Any suggestions to resolve this would be of great help.

question from:https://stackoverflow.com/questions/65939029/error-class-cooperative-groups-v1thread-block-has-no-member-is-valid

Answer 1

studying cooperative_groups.h, it appears that the only cg classes for which is_valid() method is provided are grid_group and multi_grid_group.

Therefore at this time, these are the only groups for which the method is available, you should not attempt to use that method with other group types; I think the best assumption is that other group types are always considered valid.

I suspect the logic here is that grid and multi-grid groups have proper launch configuration and platform requirements; they can be invalid. The other group types cannot be invalid (at least in those respects) to create on any supported platform or launch configuration. I don't intend that as a bulletproof statement under any possible interpretation, but a general guide or reasoning.