The following two functions P1 and P2 that share a variable B with an initial value of 2 execute concurrently.P1 ( ) { C = B - 1; B = 2 * C; }P2 ( ) { D = 2 * B; B = D - 1; }The number of distinct values that B can possibly take after the execution is ___________.

Let the statements in $P1$ be:

• $I_1: C = B - 1$

• $I_2: B = 2 \times C$

Let the statements in $P2$ be:

• $I_3: D = 2 \times B$

• $I_4: B = D - 1$

Initially, $B = 2$.

Let's analyze all possible valid interleavings of the statements:

1. $P1$ executes completely, then $P2$ executes ($I_1 \to I_2 \to I_3 \to I_4$):

   • $I_1: C = 2 - 1 = 1$

   • $I_2: B = 2 \times 1 = 2$

   • $I_3: D = 2 \times 2 = 4$

   • $I_4: B = 4 - 1 = 3$

   • Final $B = 3$

2. $P2$ executes completely, then $P1$ executes ($I_3 \to I_4 \to I_1 \to I_2$):

   • $I_3: D = 2 \times 2 = 4$

   • $I_4: B = 4 - 1 = 3$

   • $I_1: C = 3 - 1 = 2$

   • $I_2: B = 2 \times 2 = 4$

   • Final $B = 4$

3. Interleaved execution with $P1$ writing last ($I_1 \to I_3 \to I_4 \to I_2$ or $I_3 \to I_1 \to I_4 \to I_2$):

   • $I_1$ reads initial $B=2$, so $C = 2 - 1 = 1$

   • $P2$ executes ($I_3$ and $I_4$), modifying $B$

   • $I_2$ writes $B = 2 \times C = 2 \times 1 = 2$

   • Final $B = 2$

4. Interleaved execution with $P2$ writing last ($I_3 \to I_1 \to I_2 \to I_4$ or $I_1 \to I_3 \to I_2 \to I_4$):

   • $I_3$ reads initial $B=2$, so $D = 2 \times 2 = 4$

   • $P1$ executes ($I_1$ and $I_2$), modifying $B$

   • $I_4$ writes $B = D - 1 = 4 - 1 = 3$

   • Final $B = 3$

Thus, the set of distinct possible final values of $B$ is $\{2, 3, 4\}$.

The number of distinct values is 3.