CMSC132 Exam 3(Guaranteed solutions)

What is the motivation for writing multithreaded Java code? correct answers Capture logical structure of problem, better utilize hardware resources What are possible states for Java threads? correct answers New, Runnable, Running, Blocked, Dead What is the effect of invoking the start( ) method of the Thread class? correct answers Tells JVM thread is now Runnable What is the effect of invoking the join( ) method of the Thread class? correct answers Tells JVM to wait until thread is Dead before continuing execution What is scheduling? correct answers Deciding which thread(s) to run, and for how long What is the difference between preemptive and non-preemptive scheduling? correct answers Preemptive scheduling can stop threads, non-preemptive scheduling has to wait for threads to stop What are data races? correct answers Concurrent accesses to shared variable, where at least one access is a write Why should programs avoid data races? correct answers Results may differ based on scheduling, causing intermittent errors that are hard to debug What is synchronization? correct answers Coordination of events with respect to time Why should programs use synchronization? correct answers To eliminate data races in multithreaded code Properties of synchronization correct answers • May be needed in multithreaded programs to eliminate data races • Incurs runtime overhead • Excessive use can reduce performance What are Java locks? correct answers Entity associated with each Object that can be held by one thread at a time How may Java locks be used? correct answers Java locks may be used to enforce mutual exclusion (by having multiple threads attempt to hold the same lock before executing) for a region of code What are deadlocks? correct answers Threads are blocked waiting for locks with no possibility of making progress, program is unable to continue execution