# cudaFlow Algorithms » Single Task

tf::cudaFlow provides a template method, tf::cudaFlow::single_task, for creating a task to run the given callable using a single kernel thread.

## Include the Header

You need to include the header file, `taskflow/cuda/algorithm/for_each.hpp`, for creating a single-threaded task.

    #include <taskflow/cuda/algorithm/for_each.hpp>

## Run a Task with a Single Thread

You can create a task to run a kernel function just once, i.e., using one GPU thread. This is handy when you want to set up a single or a few global variables that do not need multiple threads and will be used by multiple kernels afterwards. The following example creates a single-task kernel that sets a device variable to `1`.

    int* gpu_variable;
    cudaMalloc(&gpu_variable, sizeof(int));

    tf::cudaFlow cf;
    cf.single_task([gpu_variable] __device__ () {
      *gpu_Variable = 1;
    });

    tf::cudaStream stream;
    cf.run(stream);
    stream.synchronize();

Since the callable runs on GPU, it must be declared with a `__device__` specifier.

## Miscellaneous Items

The single-task algorithm is also available in tf::cudaFlowCapturer::single_task.

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