The way the process start is a list of objects and each object has a single process and the flow starts with a service task.
Map variableMap = new HashMap();
variableMap.put("ids",idList);
variableMap.put("priority",25);
ProcessInstance processInstance = runtimeService.startProcessInstanceByKey("imageProcess", variableMap);
How can i use this priority to set the priority of the task, As my first step is a service task and the second user task is based on the priority