presto-main/src/main/java/io/prestosql/server/StageResource.java/StageResource/cancelStage
class StageResource:    @DELETE
    @Path("{stageId}")
    public void cancelStage(@PathParam("stageId") StageId stageId)
    {
        requireNonNull(stageId, "stageId is null");
        queryManager.cancelStage(stageId);
    }