Function hipGraphGetRootNodes 

pub unsafe extern "C" fn hipGraphGetRootNodes(
    graph: hipGraph_t,
    pRootNodes: *mut hipGraphNode_t,
    pNumRootNodes: *mut usize,
) -> hipError_t

@brief Returns a graph’s root nodes.

@param [in] graph - Instance of the graph to get the nodes from. @param [out] pRootNodes - Pointer to return the graph’s root nodes. @param [out] pNumRootNodes - Returns the number of graph’s root nodes. @returns #hipSuccess, #hipErrorInvalidValue

pRootNodes may be NULL, in which case this function will return the number of root nodes in pNumRootNodes. Otherwise, pNumRootNodes entries will be filled in. If pNumRootNodes is higher than the actual number of root nodes, the remaining entries in pRootNodes will be set to NULL, and the number of nodes actually obtained will be returned in pNumRootNodes.