Would a pepper spray be effective against such a large pack of dogs?
I doubt it because you've got to get each one of them up close, giving them an opportunity to hang on to your arm and you could incapacitate yourself. Dogs' eyesight is not very good anyway so knocking it out might not make much difference.
Once a dog locks on to you it won't let go. 40 years ago, while riding my motorbike through one of Bristol's less salubrious estates, a barking dog shot out and grabbed my left ankle. Fortunately I had the presence of mind to open the throttle and after about 300 yards of being held horizontal by the airstream the the runt let go and was last seen in my mirror rolling over and over, still barking. When at a safe distance I inspected my ankle and found some puncture marks reflecting its dentition, the quality of which was surprisingly good given the area.
According to some American sites the best method is to identify the alpha-dog, let it bite your hand and then shove your hand down its throat whoch will make it gag and give you the opportiunity to break its neck by pushing against the other hand. The other dogs will then immediately slink along the ground and be your best friends.
Quite a few imponderables there, but it's certainly stupid to try to pull your hand out a dog's jaws. It won't come out without lacerations. So push, what have you got to lose?