/*
* Create a thread object using the default constructor ThreadCB() and
* associate this newly created thread with a task (provided as an
* argument to the do create() method).
*
*/
public static ThreadCB do_create(TaskCB task) {
// It is important to keep in mind that each time control is transferred to
// the operating system, it is seen as an opportunity to schedule a thread
// to run. Therefore, regardless of whether the new thread was created
// successfully, the dispatcher must be called (or else a warning will be issued)
// There is a global constant (in IflThreadCB), called MaxThreadsPerTask.
// If this number of threads per task is exceeded, no new thread should be
// created for that task, and null should be returned.
if (MaxThreadsPerTask <= task.getThreadCount()) {
dispatch();
return null;
}
// To link a thread to its task, the method addThread() of class
// IflTaskCB should be used and the thread’s task must be set using
// the method setTask() of IflThreadCB.*/
ThreadCB thread = new ThreadCB();
// null should also be returned if addThread() returns FAILURE. You can
// find out the number of threads a task currently has by calling the
// method getThreadCount() on that task.
if (task.addThread(thread) == FAILURE) {
dispatch();
return null;
}
// Apparently I needed to add this after testing. 2 hours of debugging. Wow
task.addThread(thread);
thread.setTask(task);
// If priority scheduling needs to be implemented, the do create() method must cor-
// rectly assign the thread’s initial priority. The actual value of the priority depends
// on the particular scheduling policy used. OSP 2 provides methods for setting and
// querying the priority of both tasks and threads. The methods are setPriority() and
// getPriority() in classes TaskCB and ThreadCB, respectively.
thread.setPriority(randomGeneratedNumber.nextInt((10 - 1) + 1));
// Finally, the status of the new thread should be set to ThreadReady
// and it should be placed in the ready queue.
thread.setStatus(ThreadReady);
// If priority is above below 10% or equal to move into the low priority thread.
if (task.getPriority() <= 1) ThreadCB.lowPriorityQueue.addElement(thread);
else ThreadCB.highPriorityQueue.addElement(thread);
// If all is well, the thread object created by this method should be returned.
dispatch();
return thread;
}
/**
* Sets the properties of a new task, passed as an argument.
*
* <p>Creates a new thread list, sets TaskLive status and creation time, creates and opens the
* task's swap file of the size equal to the size (in bytes) of the addressable virtual memory.
*
* @return task or null @OSPProject Tasks
*/
public static TaskCB do_create() {
TaskCB new_task = new TaskCB(); // criação da nova task
HClock new_clock = new HClock(); // instância do relógio do sistema
String path = SwapDeviceMountPoint + String.valueOf(new_task.getID()); // path do swap file
new_task.new_thread = new ArrayList<ThreadCB>();
new_task.new_port = new ArrayList<PortCB>();
new_task.new_file = new ArrayList<OpenFile>();
new_task.setPageTable(new PageTable(new_task));
new_task.setCreationTime(
new_clock.get()); // usa a instância do relógio, para setar o horário de criação da task
new_task.setStatus(TaskLive); // seta o estado atual da task (TaskLive)
new_task.setPriority(1); // como não foi especificado nenhuma prioridade na descrição, usamos 1
new_task.new_swap.create(
path,
(int)
Math.pow(
2.0D,
MMU.getVirtualAddressBits())); // tamanho da página deve ser 2^(número de bits do
// ambiente)
OpenFile save_swap = OpenFile.open(path, new_task); // abrimos o swap file
new_task.setSwapFile(
save_swap); // dizemos que o swap criado acima deve ser alocado a nossa task
ThreadCB.create(new_task); // criamos a thread inicial
if (save_swap == null) { // verificamos se o swap foi criado com sucesso
new_task
.new_thread
.get(0)
.dispatch(); // caso não tenha, dispachamos a thread criada acima (posição 0 do vetor)
return null; // e retornamos uma task nula
}
return new_task; // se tudo ocorreu como esperado, retornamos a task criada inicialmente
}