計算機結構與作業系統

Regarding synchronization, $P_i$ and $P_j$ are two processes sharing the critical section with the following assumptions:

• The "load" and "store" machine-language instructions are atomic.
• The two processes share turn to indicate whose turn.

Given the following two approaches (code shown for process $P_i$; exchange $i$ and $j$ for $P_j$):

Approach 1 for Process $P_i$:

while (true) {
    turn = i;
    while (turn == j)
        ;
    /* critical section */
    turn = j;
    /* remainder section */
}

Approach 2 for Process $P_i$:

while (true) {
    while (turn == j)
        ;
    /* critical section */
    turn = j;
    /* remainder section */
}

Select correct description(s).