c++ - OpenCL get_global_id probably return -

i have suspiciton of multiple calls of opencl kernel same get_global_id(0) return value.

calling host:

err = commandqueue.enqueuendrangekernel(my_kernel, cl::nullrange, cl::ndrange(1024), cl::ndrange(256), null, null); 

and kernel:

typedef struct { float x, y; } point3;  __kernel void update_position (     __global point3* pts,     __global point3* speed,     const unsigned int count,     const float t) {      unsigned long = get_global_id(0);     if (i < count) {          pts[i].x += speed[i].x * t;         pts[i].y += speed[i].y * t;     } } 

what want update every item of 1024 pts once , once. problem running program multiple times various non-valid results. guess get_global_id(0) not return unique number between 0 , 1023 (inclusive) body of kernel executed more once.

unfortunatelly official web api of khronos being down , haven't found suitable answer/solution.

should use other function determine core/thread code runs on? or ndranges called wrong?

thanks :)