This skeleton of a program is designed so that multiple threads will be busy waiting for the next_action variable to be set. Ideally one thread would call perform_action whenever the main sets it to a nonzero. Show how mutexes and condition variables can be used to to guarantee this behavior.

// choose a time-consuming activity based on action ...

void perform_action(int action);

int next_action=0;

void* threadfunc(void*)

{

while (1)

{

while (next_action == 0);

int my_action=next_action;

next_action=0;

perform_action(my_action);

}

}

int main()

{

// assume we've spawned threads executing threadfunc ...

while (1)

{

// determine what action should be dispatched to a thread next

next_action=read_action_from_user();

// exit the program

if (next_action == -1) { break; }