//----------------------------------------------------------------------
//
// ProcessSchedule
//
// Schedule the next process to run. If there are no processes to
// run, exit. This means that there should be an idle loop process
// if you want to allow the system to "run" when there's no real
// work to be done.
//
// NOTE: the scheduler should only be called from a trap or interrupt
// handler. This way, interrupts are disabled. Also, it must be
// called consistently, and because it might be called from an interrupt
// handler (the timer interrupt), it must ALWAYS be called from a trap
// or interrupt handler.
//
// Note that this procedure doesn't actually START the next process.
// It only changes the currentPCB and other variables so the next
// return from interrupt will restore a different context from that
// which was saved.
//
//----------------------------------------------------------------------
void ProcessSchedule () {
PCB *pcb=NULL;
int i=0;
Link *l=NULL;
dbprintf ('p', "Now entering ProcessSchedule (cur=0x%x, %d ready)\n",
(int)currentPCB, AQueueLength (&runQueue));
// The OS exits if there's no runnable process. This is a feature, not a
// bug. An easy solution to allowing no runnable "user" processes is to
// have an "idle" process that's simply an infinite loop.
if (AQueueEmpty(&runQueue)) {
if (!AQueueEmpty(&waitQueue)) {
printf("FATAL ERROR: no runnable processes, but there are sleeping processes waiting!\n");
l = AQueueFirst(&waitQueue);
while (l != NULL) {
pcb = AQueueObject(l);
printf("Sleeping process %d: ", i++); printf("PID = %d\n", (int)(pcb - pcbs));
l = AQueueNext(l);
}
GracefulExit();
}
printf ("No runnable processes - exiting!\n");
GracefulExit (); // NEVER RETURNS
}
// Move the front of the queue to the end. The running process was the one in front.
AQueueMoveAfter(&runQueue, AQueueLast(&runQueue), AQueueFirst(&runQueue));
// Now, run the one at the head of the queue.
pcb = (PCB *)AQueueObject(AQueueFirst(&runQueue));
currentPCB = pcb;
dbprintf ('p',"About to switch to PCB 0x%x,flags=0x%x @ 0x%x\n",
(int)pcb, pcb->flags, (int)(pcb->sysStackPtr[PROCESS_STACK_IAR]));
// Clean up zombie processes here. This is done at interrupt time
// because it can't be done while the process might still be running
while (!AQueueEmpty(&zombieQueue)) {
pcb = (PCB *)AQueueObject(AQueueFirst(&zombieQueue));
dbprintf ('p', "Freeing zombie PCB 0x%x.\n", (int)pcb);
if (AQueueRemove(&(pcb->l)) != QUEUE_SUCCESS) {
printf("FATAL ERROR: could not remove zombie process from zombieQueue in ProcessSchedule!\n");
GracefulExit();
}
ProcessFreeResources(pcb);
}
dbprintf ('p', "Leaving ProcessSchedule (cur=0x%x)\n", (int)currentPCB);
}
//-------------------------------------------------------
//
// int MboxClose(mbox_t);
//
// Close the mailbox for use to the current process.
// If the number of processes using the given mailbox
// is zero, then disable the mailbox structure and
// return it to the set of available mboxes.
//
// Returns MBOX_FAIL on failure.
// Returns MBOX_SUCCESS on success.
//
//-------------------------------------------------------
int MboxClose(mbox_t handle) {
int i;
int length;
Link *l;
if(!&mboxs[handle]) return MBOX_FAIL;
if(!AQueueEmpty(&mboxs[handle].pids)){
length = AQueueLength(&mboxs[handle].pids);
l = AQueueFirst(&mboxs[handle].pids);
for(i=0; i < length; i++){
if((int)AQueueObject(l) == GetCurrentPid()){
AQueueRemove(&l);
break;
}
l = AQueueNext(l);
}
}
if(AQueueEmpty(&mboxs[handle].pids)){
while(!AQueueEmpty(&mboxs[handle].messages)){
l = AQueueFirst(&mboxs[handle].messages);
AQueueRemove(&l);
}
mboxs[handle].inuse = 0;
}
return MBOX_SUCCESS;
}
////////////////////////////////////////////////////////////////////
// Moves link "l" to the position after link "after" in queue "q"
////////////////////////////////////////////////////////////////////
int AQueueMoveAfter(Queue *q, Link *after, Link *l) {
if (!q) return QUEUE_FAIL;
if (!l) return QUEUE_FAIL;
if (l->queue != q) return QUEUE_FAIL; // l does not belong to q
// If after is NULL, then l is the last item on the queue,
// so we don't have to do anything
if (!after) {
if (AQueueLength(q) != 1) return QUEUE_FAIL;
if (AQueueFirst(q) != AQueueLast(q)) return QUEUE_FAIL;
return QUEUE_SUCCESS;
}
if (after->queue != q) return QUEUE_FAIL;
if (after == l) { // don't have to do anything
return QUEUE_SUCCESS;
}
// First fix Queue first/last pointers
if (q->last == l) return QUEUE_FAIL; // this would be strange if it happened
if (q->first == l) q->first = l->next;
if (q->last == after) q->last = l;
// Now remove l from it's original position in the list
if (l->next) l->next->prev = l->prev;
if (l->prev) l->prev->next = l->next;
// Now update l's prev and next pointers to put l into the list after the link "after"
l->prev = after;
l->next = after->next;
// Now fix the list around l
after->next = l;
if (l->next) l->next->prev = l;
return QUEUE_SUCCESS;
}
//-------------------------------------------------------
//
// int MboxRecv(mbox_t handle, int maxlength, void* message);
//
// Receive a message from the specified mailbox. The call
// blocks when there is no message in the buffer. Maxlength
// should indicate the maximum number of bytes that can be
// copied from the buffer into the address of "message".
// An error occurs if the message is larger than maxlength.
// Note that the calling process must have opened the mailbox
// via MboxOpen.
//
// Returns MBOX_FAIL on failure.
// Returns number of bytes written into message on success.
//
//-------------------------------------------------------
int MboxRecv(mbox_t handle, int maxlength, void* message) {
int i;
int qlen;
Link *l;
int exists = 0;
mbox_message *m;
//check if mailbox is real
if(!&mboxs[handle]) return MBOX_FAIL;
//check if pid opened this mailbox
if(!AQueueEmpty(&mboxs[handle].pids ) ){
qlen = AQueueLength(&mboxs[handle].pids);
l = AQueueFirst(&mboxs[handle].pids);
for(i=0; i < qlen; i++){
if((int)AQueueObject(l) == GetCurrentPid()){
exists = 1;
break;
}
l = AQueueNext(l);
}
//actualy checks if pid exists
if(exists == 0){
return MBOX_FAIL;
}
//wait until queue has something in it
if(SemHandleWait(mboxs[handle].s_msg_full) == SYNC_FAIL){
printf("bad sem handle wait in mbox recv\n");
exitsim();
}
//lock
if(LockHandleAcquire(mboxs[handle].l) != SYNC_SUCCESS){
printf("FATAL ERROR: could not get lock in Mbox send!\n");
exitsim();
}
l = AQueueFirst(&mboxs[handle].messages);
m = (mbox_message *) l->object;
//check if message longer than max length
if(m->length > maxlength) {
return MBOX_FAIL;
}
//copy message to local variable
dstrncpy(message,(void*) m->message, m->length);
//reset structure for use elsewhere
m->inuse =0;
//delete link
AQueueRemove(&l);
//unlock
if(LockHandleRelease(mboxs[handle].l) != SYNC_SUCCESS){
printf("FATAL ERROR: could not release lock in Mbox send!\n");
exitsim();
}
if(SemHandleSignal(mboxs[handle].s_msg_empty) == SYNC_FAIL){
printf("bad sem handle signal in mbox recv\n");
exitsim();
}
}else{
return MBOX_FAIL;
}
return MBOX_SUCCESS;
}
//-------------------------------------------------------
//
// int MboxSend(mbox_t handle,int length, void* message);
//
// Send a message (pointed to by "message") of length
// "length" bytes to the specified mailbox. Messages of
// length 0 are allowed. The call
// blocks when there is not enough space in the mailbox.
// Messages cannot be longer than MBOX_MAX_MESSAGE_LENGTH.
// Note that the calling process must have opened the
// mailbox via MboxOpen.
//
// Returns MBOX_FAIL on failure.
// Returns MBOX_SUCCESS on success.
//
//-------------------------------------------------------
int MboxSend(mbox_t handle, int length, void* message) {
int i;
int qlen;
Link *l;
int exists = 0;
//check if mailbox is real
if(!&mboxs[handle]) return MBOX_FAIL;
//check if pid opened this mailbox
if(!AQueueEmpty(&mboxs[handle].pids ) ){
qlen = AQueueLength(&mboxs[handle].pids);
l = AQueueFirst(&mboxs[handle].pids);
for(i=0; i < qlen; i++){
if((int)AQueueObject(l) == GetCurrentPid()){
exists = 1;
break;
}
l = AQueueNext(l);
}
//actuall checks if pid exists
if(exists == 0){
return MBOX_FAIL;
}
//check if message longer than max length
if(length > MBOX_MAX_MESSAGE_LENGTH) {
return MBOX_FAIL;
}
//check for space in mailbox
if((SemHandleWait(mboxs[handle].s_msg_empty)) == SYNC_FAIL ){
printf("bad sem handle wait in mbox send\n");
exitsim();
}
//lock
if(LockHandleAcquire(mboxs[handle].l) != SYNC_SUCCESS){
printf("FATAL ERROR: could not get lock in Mbox send!\n");
exitsim();
}
for(i=0; i<MBOX_NUM_BUFFERS; i++){
if(mbox_messages[i].inuse == 0){
mbox_messages[i].inuse = 1;
break;
}
}
//creating mbox_message structure
dstrncpy(mbox_messages[i].message, (char *) message, length);
mbox_messages[i].length = length;
if ((l = AQueueAllocLink(&mbox_messages[i])) == NULL) {
printf("FATAL ERROR: could not allocate link for pid queue in Mbox Open!\n");
exitsim();
}
//add message to end of queue
AQueueInsertLast(&mboxs[handle].messages, l);
//unlock
if(LockHandleRelease(mboxs[handle].l) != SYNC_SUCCESS){
printf("FATAL ERROR: could not release lock in Mbox send!\n");
exitsim();
}
if(SemHandleSignal(mboxs[handle].s_msg_full) == SYNC_FAIL){
printf("bad sem handle signal in mbox send\n");
exitsim();
}
}else{
return MBOX_FAIL;
}
return MBOX_SUCCESS;
}
// Returns true is the queue is empty, false otherwise
int AQueueEmpty (Queue *q) { return (AQueueLength (q) == 0); }
//-------------------------------------------------------
//
// int MboxRecv(mbox_t handle, int maxlength, void* message);
//
// Receive a message from the specified mailbox. The call
// blocks when there is no message in the buffer. Maxlength
// should indicate the maximum number of bytes that can be
// copied from the buffer into the address of "message".
// An error occurs if the message is larger than maxlength.
// Note that the calling process must have opened the mailbox
// via MboxOpen.
//
// Returns MBOX_FAIL on failure.
// Returns number of bytes written into message on success.
//
//-------------------------------------------------------
int MboxRecv(mbox_t handle, int maxlength, void* message) {
int intrs;
int wasFull = 0, buffersSaturated = 0;
mbox_message * user_mesg;
Link *l;
if(MailBox[handle].inuse == false)
{
printf("Currently passed mailbox handle : %d by calling process : %d is unallocated\n", handle, GetCurrentPid());
return MBOX_FAIL;
}
if(MailBox[handle].procs_link[GetCurrentPid()] == false)
{
printf("Mailbox : %d not already opened by calling proces :%d\n", handle, GetCurrentPid());
return MBOX_FAIL;
}
intrs = DisableIntrs();
LockHandleAcquire(MailBox[handle].lock);
while(AQueueLength(&MailBox[handle].buffers) == 0)
{
//printf("Waiting for mailbox to have more messages\n");
CondHandleWait(MailBox[handle].moreData);
}
//printf("Received mailbox lock by calling process : %d with mailbox buffer count : %d\n", GetCurrentPid(), AQueueLength(&MailBox[handle].buffers));
if(AQueueLength(&MailBox[handle].buffers) == MBOX_MAX_BUFFERS_PER_MBOX)
wasFull = 1;
if(AQueueLength(&MailBox[handle].buffers) < MBOX_MAX_BUFFERS_PER_MBOX && used_buffers == MBOX_NUM_BUFFERS)
buffersSaturated = 1;
//printf("Obtained message in receiver : %d from buffer index : %d\n", user_mesg->size, (user_mesg - Messg_Buffers));
if((user_mesg = (mbox_message *)AQueueObject(MailBox[handle].buffers.first)) == NULL)
{
printf("Undefined/unallocated Link pointer obtained from mailbox queue with handle :%d in process : %d\n", handle, GetCurrentPid());
//printf("MailBox buffer size : %d\n", AQueueLength(&MailBox[handle].buffers));
return MBOX_FAIL;
}
if(maxlength < user_mesg->size)
{
printf("Message : %s requested by user process : %d larger than acceptable message length : %d (Messge length received : %d)\n", user_mesg->message, GetCurrentPid(), maxlength, user_mesg->size);
return MBOX_FAIL;
}
bcopy(user_mesg->message, message, user_mesg->size);
l = MailBox[handle].buffers.first;
MailBox[handle].buffers.first = AQueueNext(MailBox[handle].buffers.first);
if(AQueueRemove(&l) == QUEUE_FAIL)
{
printf("FATAL Error : Message object Link for buffer : %d received by process : %d could not be removed from queue of mailbox handle : %d",used_buffers, GetCurrentPid(), handle);
exitsim();
}
used_buffers--;
//if(wasFull || buffersSaturated)
CondHandleSignal(MailBox[handle].moreSpace);
LockHandleRelease(MailBox[handle].lock);
RestoreIntrs(intrs);
return user_mesg;
}
//-------------------------------------------------------
//
// int MboxSend(mbox_t handle,int length, void* message);
//
// Send a message (pointed to by "message") of length
// "length" bytes to the specified mailbox. Messages of
// length 0 are allowed. The call
// blocks when there is not enough space in the mailbox.
// Messages cannot be longer than MBOX_MAX_MESSAGE_LENGTH.
// Note that the calling process must have opened the
// mailbox via MboxOpen.
//
// Returns MBOX_FAIL on failure.
// Returns MBOX_SUCCESS on success.
//
//-------------------------------------------------------
int MboxSend(mbox_t handle, int length, void* message) {
int intrs;
int wasEmpty = 0;
Link * mbuffer_link;
if(MailBox[handle].inuse == 0)
{
printf("Currently passed mailbox handle : %d by calling process : %d is unallocated\n", handle, GetCurrentPid());
return MBOX_FAIL;
}
if(MailBox[handle].procs_link[GetCurrentPid()] == false)
{
printf("Mailbox : %d not already opened by calling proces :%d\n", handle, GetCurrentPid());
return MBOX_FAIL;
}
intrs = DisableIntrs();
LockHandleAcquire(MailBox[handle].lock);
while(AQueueLength(&MailBox[handle].buffers) == MBOX_MAX_BUFFERS_PER_MBOX || used_buffers == MBOX_NUM_BUFFERS)
{
CondHandleWait(MailBox[handle].moreSpace);
}
//printf("Buffer size of queue before inserting messager by : %d is : %d\n", GetCurrentPid(), AQueueLength(&MailBox[handle].buffers));
if(AQueueLength(&MailBox[handle].buffers) == 0)
wasEmpty = 1;
if(AQueueLength(&MailBox[handle].buffers) != MBOX_MAX_BUFFERS_PER_MBOX)
{
if(length > MBOX_MAX_MESSAGE_LENGTH)
{
printf("Messge passed by user process : %d larger than accepted message length (Messge length sent - %d)", GetCurrentPid(), length);
return MBOX_FAIL;
}
bcopy(message, Messg_Buffers[used_buffers++].message, 8);
Messg_Buffers[used_buffers - 1].size = length;
//printf("Original Message : %s Copied : %s in : %d\n", (char *)message, (char *)(Messg_Buffers[used_buffers - 1].message), handle);
if((mbuffer_link = AQueueAllocLink(&Messg_Buffers[used_buffers - 1])) == QUEUE_FAIL)
{
printf("FATAL Error : Link object could not be created for message buffer : %d in process : %d",used_buffers - 1, GetCurrentPid());
exitsim();
}
if(AQueueInsertLast(&MailBox[handle].buffers, mbuffer_link) != QUEUE_SUCCESS)
{
printf("FATAL Error : Link object could not be created for message buffer : %d in process : %d",used_buffers - 1, GetCurrentPid());
exitsim();
}
}
//printf("Message inserted by process : %d using buffer : %d with current count : %d\n", GetCurrentPid(), buffer_no, AQueueLength(&MailBox[handle].buffers));
//if(wasEmpty)
CondHandleSignal(MailBox[handle].moreData);
LockHandleRelease(MailBox[handle].lock);
RestoreIntrs(intrs);
return MBOX_SUCCESS;
}
