This problem studies the interaction between real$-$time scheduling and mutual ex$-$

clusion, and was formulated by Kevin Weekly.

Consider the following excerpt of code:

$1$ pthread$\_$mutex$\_$t X; $//$ Resource X: Radio communication

$2$ pthread$\_$mutex$\_$t Y; $//$ Resource Y: LCD Screen

$3$ pthread$\_$mutex$\_$t Z; $//$ Resource Z: External Memory $($slow$)$

$4$

$5$ void ISR$\_$A$()\{//$ Safety sensor Interrupt Service Routine

$6$ pthread$\_$mutex$\_$lock$($&Y$)$;

$7$ pthread$\_$mutex$\_$lock$($&X$)$;

$8$ display$\_$alert$()$; $//$ Uses resource Y

$9$ send$\_$radio$\_$alert$()$; $//$ Uses resource X

$10$ pthread$\_$mutex$\_$unlock$($&X$)$;

$11$ pthread$\_$mutex$\_$unlock$($&Y$)$;

$12\}$

$13$

$14$ void taskB$()\{//$ Status recorder task

$15$ while $(1)\{$

$16$ static time$\_$t starttime $=$ time$()$;