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| Question | Answer |
| What is 211 | A drop out module lol |
| Define Concurrency | 1 - Is a way on how multiple, independent processes behave when running and interacting with each other |
| How can we use Java Threads | 1 - Define a class which Implements Runnable 2 - Create your objects 2 - Implementation of a run() method |
| What is a Processor | 1 - Device that runs instructions and can have multiple processes |
| What is a Process and where does it reside | 1 - Active system entity 2 - Resides in main memory |
| What is a Program | 1 - Literal Application or system 2 - Program may be executed by multiple processes at the same time |
| What is the Difference between Parallel and Concurrent | 1 - Parallel is multiple processes executing simultaneously. All of them execute 2 - Concurrency is that multiple processes are underway and can execute at a given instant |
| What does a Scheduler guarantee and not guarantee | 1 - Guarantees that the code will eventually run. 2 - Doesn't guarantee fairness and timeliness. 3 - Fairness - run at the same time 4 - timeliness - complete in a desirable time frame |
| What is Safe Concurrency | 1 - No shared data or communication 2 - Read only data |
| What is Risky Concurrency | 1 - There is a shared resource and there is no synchronization 2 - A resource which can be modified by 1 or more threads |
| What is Synchronization | 1 - Mechanism to ensure multiple processes or threads do not simultaneously execute |
| What is Competition | 1 - Competing for a variable that 2 processes want to read or update simultaneously 2 - Ensures multiple threads don't execute within the critical section |
| What is Coordination | 1 - One process tells another process that a result is now available |
| What's the critical section | 1 - Region of code that you want protected from shared resource access |
| What is a Race Condition | 1 - When more than 1 thread can access the critical section at the same time 2 - error that occurs when multiple processes are racing in an uncontrolled manner |
| What is the Difference between indeterminate and deterministic results | 1 - Indeterminate - We may get different results everytime 2 - Determinate - We get the same result every time |
| What is Mutual Exclusion | 1 - Where only one thread can run with in the critical section |
| What is bounded waiting | 1 - Threads waiting to enter the section will eventually enter 2 - Threads which are in the section will eventually leave |
| What is Atomicity and a solution for this | 1 - Where person X and Y are writing a novel 2 - Must ensure that they do not work on the same chapter 3 - A solution could be mutual exclusion |
| What is Conditional Synchronization | 1 - Where one thread must finish before another thread starts |
| Problems and solutions for concurrency management | 1 - Competition -> Mutex 2 - Coordination - Cond Sync |
| Define Locks | 1 - Mutual exclusion mechanism that limits resource access in a multi-threaded environment |
| Name and Describe the 2 states of a Lock | 1 - Held - A thread is in the critical section. No one should enter 2 - Not Held - No thread is in the section. Thread can enter |
| Name and describe 2 operations of the Lock | 1 - Acquire - Mark the lock as held 2 - Release - mark the lock as not held |
| How can you declare a Lock | 1 - Like a variable 2 - Lock L |
| Where do you call Acquire and Release in the Critical section | 1 - Call acquire at the start of the section 2 - Call release at the end of the section |
| What is the Synchronized statement and where is it called | 1 - A mutual exclusion in java. 2 - Like an implicit lock 3 - used by the "synchronized" key word. eg public void SYNCHRONIZED |
| What is Context switching | 1 - The idea of switching to threads and processes RE READ THIS TOPIC.... |
| What is the 3 step context switching sequence | 1 - De-Schedule current thread 2 - Scheduler selects best ready thread to run using priority, time slicing 3 - Resume new selected thread |
| What is a Semaphore | 1 - Locks provide mutex 2 - Semaphores is the ability to have more than 1 lock. 3 - Allows multiple threads to enter the critical section |
| Why would be use semaphores and the problems that can occur | 1 - may want more threads or place ordering 2 - Problems such as the producer consumer problem |
| What are the operations of the semaphore | 1 - Wait() - Decrements the counter by 1. If the counter is at 0. No more threads can enter. Threads are put into the queue 2 - Signal() - Increments the counter by 1. |
| What happens when Wait() is called by a thread | 1 - If semaphore is open, continue 2 - If semaphore closed, then go to the queue |
| What happens when Signal() is called | 1 - If thread is on queue, then unblock it 2 - If there is no queue, then remember it for next thread |
| What are the operations of an intrinsic wait queue and what does each one do | 1 - Object.wait() - put thread to a stack 2 - Object.Notify() - take threads from stack and make it runnable |
| What is a Spurious Wakeup | 1 - Wake up all threads that you dont want to wake up 2 - Done via the NotifAll() 3 - Doesnt re-check the condition |
| What is the Producer Consumer Problem | 1 - producer creates 2 - Consumer will take 3 - Consumer cant take anything if nothing is there 4 - if full, stop producing 5 - if empty stop consuming |
| Define what is Message Passing | 1 - Type of interprocess communication 2 - Processes communicate by sending and receiving messages using primitives |
| How does Message Passing work | 1 - Processes communicate by sending and receiving message |
| Define the Different channels of Message Passing | 1 - Local memory channel - When interacting processes are located on the same processor 2 - Physical communication - When interacting processes are located on different processors |
| What are the Primitives of Message passing | 1 - Send - Send message to channel - send(msg, chan) 2 - Receive - Receive a value from a channel - var = receive (chan) |
| What is the Difference between synchronous and asynchronous | 1 - synchronous is that the sender and receiver wait for each other 2 - asynchronous is that the sender and receiver do not wait for each other |
| What happens in a Blocking Operation in Message Passing | 1 - Send - blocks until message received by receiver 2 - Receive - Blocks until message is available |
| What happens in a non-blocking operations | 1 - Send - Process resumes with life after message is sent 2 - Receiver retrieves valid message |
| What are the problems with Synchronous | 1 - Reduced concurrency - When 2 processes communicate, one of them will have to block |
| What are the problems with Asynchronous | Acknowledgement - Receiver cannot know anything about state of sender. Sender has no way of knowing if message was sent or received unless receiver replies back |
| What is a spin lock | 1 - Lock that keeps spinning and checking if its free or not 2 - Improves performance and CPU usage |
| What does Spin locking Violate and possible solutions for this | 1 - Violates mutual exclusion as there could be 2 threads with the same lock 2 - Solutions could include disable interrupts |
| What is disable interrupts | 1 - No context switch in critical section 2 - Really bad |
| What is a Blocking lock and advantage s and disadvantages of it | 1 - Scheduler blocks threads while they wait 2 - Good for long sections 3 - bad if locks are accessed a lot of time |
| What is a Spinning lock and advantage s and disadvantages of it | 1 - Loop a lock until acquiring 2 - Good for short section 3 - Costly for long sections |
| What is a monitor, an example of a monitor and difference between a monitor and a lock | 1 - Monitor can perform mutex 2 - Example of a monitor is the synchronized keyword 3 - Monitor is a construct 4 - Lock is a primitive |
| What is the Thundering Herd Problem | 1 - When you do notifyAll() 2 - Stampede to the section, 3 - waste of cpu cycles |
| What is a Barrier | 1 - Processes cannot proceed the barrier until all threads have reached the barrier 2 - How you cooperate |
| What is a Priority Based Barrier | 1 - Allows us to choose which thread with the highest priority can resume and proceed with the barrier |
| What is a bounded barrier | 1 - The limit on the amount of threads in a barrier |
| What is a User Thread and advantage sna disadvantages of this. What is it most useful for | 1 - Supported in user level library 2 - Advantage - No OS Support required - Cheap context switch 3 - Disadvantage - cant execute on a multicore lmao 4 - useful for GUI servers and web servers |
| What is a Kernel Thread and advantage sna disadvantages of this. What is it most useful for | 1 - Only knows about the process, is pre emptible 2 - advantage - more concurrent 3 - disadvantage - |
| What is a deadlock, how we deal with them | 1 - 2 or more threads forever waiting 2 - ABBA - lock lock unlock unlock 3 - PRogram design so circular wait never occurs |
| What is a livelock | 1 - Process cannot make progress 2 - Livelock can be solved, |
| What is starvation | 1 - Process isn't getting regular access to shared resource enough |
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