#include #include #include #include #define NUM_LOAVES_PER_BATCH 7 #define NUM_BATCHES 6 #define NUM_LOAVES_TO_EAT 14 /** This system has four threads: the duck, cat, and dog that eat bread, and the little red hen that makes the bread. The little red hen makes seven loaves per batch, but she only has the patience for six batches. The little red hen only makes a batch if there are no loaves left. The other three animals each want to eat 14 loaves of bread, but only one of them can be in the kitchen at a time (to avoid fights over who gets what bread). When the duck, cat, or dog notices that there are no loaves of bread available, they complain to the little red hen and wait (in the kitchen) for the next batch to be ready. Use semaphores to enforce this constraint. Note: the global numLoaves variable should be left as is (i.e. do not make it a semaphore). **/ int numLoaves; void *littleRedHenThread(void *arg) { char *name = (char*)arg; int batch; for (batch = 1; batch <= 6; batch++) { sleep(2); // just makes it obvious that it won't work without // semaphores numLoaves += 7; printf("%-20s: A fresh batch of bread is ready. ", name); } printf("%-20s: I'm fed up with feeding you lazy animals! " "No more bread! ", name); return NULL; } void *otherAnimalThread(void *arg) { char *name = (char*)arg; int numLoavesEaten = 0; while (numLoavesEaten < NUM_LOAVES_TO_EAT) { if (numLoaves <= 0) { printf("%-20s: Hey, Little Red Hen, make some more bread! ", name); } numLoaves--; printf("%-20s: Mmm, this loaf is delicious. ", name); numLoavesEaten++; if (random() > random()) { // Adds variety to output sleep(1); } } printf("%-20s: I've had my fill of bread. Thanks, Little Red Hen! ", name); return NULL; } int main(int argc, char **argv) { pthread_t dog, cat, duck, hen; numLoaves = 0; char dogName[] = "Lazy Dog"; char catName[] = "Sleepy Cat"; char duckName[] = "Noisy Yellow Duck"; char henName[] = "Little Red Hen"; pthread_create(&dog, NULL, otherAnimalThread, dogName); pthread_create(&cat, NULL, otherAnimalThread, catName); pthread_create(&duck, NULL, otherAnimalThread, duckName); pthread_create(&hen, NULL, littleRedHenThread, henName); pthread_join(dog, NULL); pthread_join(cat, NULL); pthread_join(duck, NULL); pthread_join(hen, NULL); printf("Everything finished. "); } 

And the Sample output:

Sleepy Cat : Hey, Little Red Hen, make some more bread! Little Red Hen : A fresh batch of bread is ready. Sleepy Cat : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Lazy Dog : Hey, Little Red Hen, make some more bread! Little Red Hen : A fresh batch of bread is ready. Lazy Dog : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Noisy Yellow Duck : Hey, Little Red Hen, make some more bread! Little Red Hen : A fresh batch of bread is ready. Noisy Yellow Duck : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Noisy Yellow Duck : Hey, Little Red Hen, make some more bread! Little Red Hen : A fresh batch of bread is ready. Noisy Yellow Duck : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Sleepy Cat : Hey, Little Red Hen, make some more bread! Little Red Hen : A fresh batch of bread is ready. Sleepy Cat : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Sleepy Cat : Hey, Little Red Hen, make some more bread! Little Red Hen : A fresh batch of bread is ready. Little Red Hen : I'm fed up with feeding you lazy animals! No more bread! Sleepy Cat : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Noisy Yellow Duck : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Lazy Dog : Mmm, this loaf is delicious. Sleepy Cat : Mmm, this loaf is delicious. Noisy Yellow Duck : I've had my fill of bread. Thanks, Little Red Hen! Lazy Dog : Mmm, this loaf is delicious. Lazy Dog : I've had my fill of bread. Thanks, Little Red Hen! Sleepy Cat : I've had my fill of bread. Thanks, Little Red Hen! Everything finished.