Consider four binary semaphores, $\backslash (\backslash$mathrm$\{$U$\},\backslash$mathrm$\{$V$\},\backslash$mathrm$\{$W$\}\backslash ),$ and X $.$ They all were initially set to $1.$ Consider also four threads, $\backslash (\backslash$mathrm$\{$T$\}\_\{1\},\backslash$mathrm$\{$~T$\}\_\{2\},\backslash$mathrm$\{$~T$\}\_\{3\}\backslash ),$ and $\backslash (\backslash$mathrm$\{$T$\}\_\{4\}\backslash ),$ executing the following sequences of code $($moving downward$).$ Currently, they have reached the inside of the functions which the arrows point to$.$

$1.[6$ points$]$ We use Resource Allocation Graph $($RAG$)$ to model this problem: each semaphore represents a single$-$unit resource, and the sem$\_$wait$()$ and sem post$()$ operations represent resource requests and resource releases, respectively. Recall that the RAG changes as the time goes by$.$ All four threads currently have reached the inside of the functions which the arrows point to$.$ Draw the up$-$to$-$date RAG at the current situation.

$2.[2$ points$]$ Based on the RAG from above, some threads are stuck in deadlock. List all such threads.

$3.[3$ points$]$ Propose a deadlock avoidance solution on how to avoid the above deadlock. Hint: follow the example of printer and plotter in class to find the positions like T to decide whether it should delay the request.