CONCURRENCY AND SYNCHRONIZATION

what components do threads share?

code, heap, global/static variables, and file descriptors

what do threads not share?

registers, stack, and TCB

what is stored in each TCB:

thread id, state, priority, used register, stack location and pointer, local variables, program counter

what is a thread?

a unit of execution within a process

what is TCB?

a data struct inside the kernel that holds thread specific info

what does p_thread_join(thread_id) do?

it makes the main thread wait until the specified thread exits

what is a critical section?

what is progress? if no other thread is accessing a critical section, a thread will

A piece of code that access a shared resource

How do we avoid multiple threads accessing a shared resource at the same time?

ensure mutual exclusion, progress, and bounded wait

what is mutual exclusion?

condition that only one thread can access a critical section at a time

what is progress?

if no other thread is accessing a critical section, a thread will

what is bounded wait?

once a thread starts trying to enter a critical section, there is a count on the number of other threads that can enter before it does

what is race condition?

when results depend on the timing

what is a mutex?

a synchronization primitive that acts as a lock for a thread in a critical section

how would you make a mutex?

pthread_mutex name;

what is the purpose of pthread_mutex_create(&name)?

it makes a pointer to the mutex object

what is course grained locking:

one big lock used anytime when a critical section is accessed

what is fine grained locking:

different locks used for different resources

what advantage does fine grained locking give:

higher concurrency

what disadvantage does FGL give:

higher risk of deadlock

what is spinning:

when a thread is wasting time constantly checking a condition

what is a condition variable:

an explicit queue that threads can put themselves on when a condition isnt as desired

how do you declare a condition variable:

pthread_cond_t name;

what does pthread_cond_wait(&c,&m) do?

puts a thread in the condition variable c and releases the mutex m atomically

what does pthread_cond_signal(&c) do?

it wakes one thread waiting in the queue

why must you always hold the lock while signaling?

to prevent a race condition where it signals before a thread is put in queue

what is a monitor?

a structure that encapsulates both condition variable and mutex