{ "q08": { "type": "blank", "question": "\n\nTo avoid spin waiting, we can use a ____ to create an explicit queue that\nthreads can put themselves on when some state of execution is not as\ndesired. When another thread changes said state, it can wake a ____ thread\nand allow them to continue by ____ on the object.\n\n\n" }, "q09": { "type": "multiple", "question": "\n\nRegarding the producer / consumer implementation in Figure 30.6, why is it\nconsidered a broken solution (select all that apply)?\n\n\n", "responses": { "early": "To prevent from waking up too early, the condition variable should be locked.", "waiting": "The code waits while holding the mutex.", "critical": "It is possible for multiple threads to be in the critical section.", "signal": "The code signals all threads rather than having producers notify consumers and consumers notify producers.", "change": "It is possible for the state of the bounded before to change between when a thread is signaled and when it is woken up." } }, "q10": { "type": "blank", "question": "\n\nTo fix the broken solution in Figure 30.6, we first need to use ____ to\ncheck the condition. Doing so will allow us to handle ____, which happens\nwhen a multiple threads are woken up even though only one signal has taken\nplace. Second, we need to have two conditions such that the producer waits\non the ____ condition and signals ____. Conversely, the consumer waits on\n____ and signals ____.\n\n\n" }, "q02": { "type": "multiple", "question": "\n\n Regarding coarse vs fine-grained locking, which of the following\n statements are true (choose all that apply)?\n\n\n", "responses": { "bkl": "The big kernel lock (BKL) is an example of coarse-grained locking.", "different": "Fine-grained locking increases concurrency by protecting different data structures with different locks.", "coarse": "Coarse-grained locking is safer since it protects more critical sections.", "one": "Coarse-grained locking increases concurrency because only one lock needs to be acquired rather than many." } }, "q03": { "type": "blank", "question": "\nTo evaluate different locking mechanisms, we need to consider three basic criteria:\n\n
    \n\n
  1. ____: Whether or not the lock actually prevents multiple threads from\nentering a critical section.
    2. \n\n
  2. ____: Whether or not each thread contending for the lock gets a fair\nshot at acquiring it.
    3. \n\n
  3. ____: How much overhead is added by using the locking mechanism.
    4. \n\n
\n\n\n" }, "q01": { "type": "blank", "question": "\n\n\nWhen using threads, we can protect a critical section by employing a ____.\nTo do so, we must first declare a ____ which holds the state of the object\nat any instant in time. This object is either ____, which means no thread\nholds the object, or ____, which means exactly one thread (aka the ____)\nholds the object and is in the critical section.\n\n\n" }, "q06": { "type": "blank", "question": "\n\nTo make a data structure ____, that is ensure it provides correct\nconcurrent access to data, we can utilize a ____, where locks are acquired\nand released automatically as you can and return from object methods.\n\n" }, "q07": { "type": "multiple", "question": "\n\n\nWhich of the following statements are true regarding implementing\nconcurrent lists, queues, and hash tables (sellect all that apply)?\n\n\n", "responses": { "lock": "We should only lock portions of methods that actually access the shared data resources.", "flow": "We should be wary of code that has many returns or exits as that can make it difficult to manage our locks.", "concurrency": "We should generally add more concurrency to make things faster.", "nested": "We should avoid building data structures consisting of nested concurrent data structures due to complexity and performance issues." } }, "q04": { "type": "multiple", "question": "\n\nTo implement locks, we need support from the hardware. Which of the\nfollowing statements about different locking mechanisms are true (select\nall that apply)?\n\n\n", "responses": { "compareandswap": "Compare-and-Swap provides a machine instruction that allows us to test a value, update it if it is the expected value, and return the actual value at that memory location.", "interrupts": "Although simple, disabling interrupts has numerous problems as a locking mechanism.", "fetchandadd": "Fetch-And-Add can be used to implement a ticket lock, which guarantees progress for all threads.", "loadlink": "Load-Linked and Store-Conditional instructions work together to atomically fetch a value and update it.", "testandset": "Test-and-Set provides a machine instruction that allows us to test the old value at a memory location and while simultaneously setting the memory location to a new value." } }, "q05": { "type": "multiple", "question": "\n\nRegarding spin locks, which of the following statements are true (select\nall that apply)?\n\n", "responses": { "fairness": "Spin locks are both correct and guarantee fairness.", "waiting": "Spin-waiting is inefficient because a thread wastes CPU resources simply waiting for another thread to release a lock", "futex": "A futex is a mutex implemented on the filesystem.", "yielding": "Yielding allows a thread to deschedule itself when it discovers the lock it wants is being held.", "parking": "Parking involves putting a thread to sleep temporarily and into a queue that will be used to select the next thread to wake up." } } }