We are writing a thread$-$safe queue. We are using a mutex lock and a condition variable nonempty. Our function dequeue$()$ should block if the queue is empty $($length $==0)$ until another threads adds a value to the queue and signals nonempty. Which of the following code fragments will accomplish this? We are writing a thread$-$safe queue. We are using a mutex lock and a condition variable nonempty. Our function dequeue$()$ should block if the queue is empty $($length $==0)$ until another threads adds a value to the queue and signals nonempty. Which of the following code fragments will accomplish this? pthread$\_$cond$\_$wait$($&nonempty, &lock$)$; if $($length $==0)\{$ pthread$\_$cond$\_$wait$($&nonempty, &lock$)$; $\}$ while $($length $==0)\{$ pthread$\_$cond$\_$wait$($&nonempty, &lock$)$; $\}$ do $\{$ pthread$\_$cond$\_$wait$($&nonempty, &lock$)$; $\}$ while $($length $==0)$; All of the above None of the above