int mythread_mutex_lock(mythread_mutex_t *mutex)
{
int lockstatus;
mythread_enter_kernel();
mutex->noofwaitingthreads=mutex->noofwaitingthreads+1;
mythread_leave_kernel();
if(mutex->lockvariable==-1)// if the lock was already destroyed then return the error code
{
return 1; // error code
}
lockstatus=testandtestandset(&(mutex->lockvariable)); // a lockstatus of 0 denotes a successful acquiring of lock
while(lockstatus==1) // if the lock acquiring fails after 100 tries , then the thread is blocked and put in a queue until lock becomes available
{
mythread_enter_kernel();
mutex->noofblockedthreads=mutex->noofblockedthreads+1;
mythread_block((mutex->blocked_threads),0);// actual 0
lockstatus=testandtestandset(&(mutex->lockvariable)); // thread that returns from the block state tries to acquire the lock again
}
mythread_enter_kernel();
mutex->owner_thread=mythread_self();
mythread_leave_kernel();
return lockstatus;
}
int mythread_scheduler(){
mythread_t self = mythread_self();
/*Limiting number of priority queues to 10 */
if(self->preemptions < 10){
self->preemptions += 1;
}
self->attr.attr = pow(2,self->preemptions); /*Since preemptions = invocation -1 */
mythread_block(mythread_readyq(),1);
return 0;
}
/*
* Will block the thread if needed, otherwise will just decrement
* the semaphore's value
*
* @Param - Pointer to the semaphore that will impose waiting
*/
void mysem_wait(Semaphore* sem){
DISABLE_INTERRUPTS();
sem->value--;
tcb* currentThread = get_mythread();
if(sem->value < 0){
mythread_block(currentThread);
block_thread(sem, currentThread);
mysem_printQueue(sem);
}
ENABLE_INTERRUPTS();
// Stall the thread until the thread becomes READY
while(currentThread->state==BLOCKED){
asm("nop");
}
}
int mythread_mutex_lock (mythread_mutex_t *mutex)
{
// if mutex is not poinitng to anything valid then return EINVAL
if (!mutex)
return EINVAL;
if (mutex->value == -1)
return EINVAL;
int retry = 0;
while (1)
{
mythread_enter_kernel();
// check if lock is available for atmost 50 times
while ((mutex->value == 1) && (retry < RETRY_MAX))
{
retry++;
}
// if we waited for 50 times and lock still not avaialable then break from he loop and block the current thread.
if (retry == RETRY_MAX)
{
break;
}
// if lock is avaialable, grab it atomically using compare and swap function
if (compare_and_swap (&mutex->value, 1, 0)==0)
{
// update the current owner to mutex to current thread
mutex->thread = mythread_self();
mythread_leave_kernel();
return 0; // success
}
} // end of while loop
// if lock is not available after 50 tries, block the current thread.
mythread_block (&mutex->queue, BLOCKED);
return 0; // success
}
int mythread_barrier_wait (mythread_barrier_t *barrier)
{
// if barrier does not exist or if it was previously destroyed, then return error code.
if (!barrier)
return EINVAL;
if (barrier->init_count == -1)
return EINVAL;
int i;
mythread_enter_kernel();
// A thread called wait, decrement the counter by 1.
if (barrier->count > 0)
barrier->count--;
// if this is the last thread calling the wait
if (barrier->count == 0)
{
// reinitialize the barrier count before unblocking rest of threads, so that the barrier can be reused
barrier->count = barrier->init_count;
// there should exactly be (init_count - 1) number of threads in the queue at this point. Unblock all of them.
for (i = 0; i < barrier->init_count -1; i++)
{
mythread_unblock (&barrier->queue, 0);
mythread_enter_kernel ();
}
mythread_leave_kernel();
// only the last thread returns MYTHREAD_BARRIER_SERIAL_THREAD while rest of threads return 0.
return MYTHREAD_BARRIER_SERIAL_THREAD; // success
}
// if this is not the last thread calling wait, block the current thread.
else
mythread_block (&barrier->queue, 1);
return 0; // success
}
