OS Implementations

• Busy wait is not tolerated in an OS!!
• Bounded wait is to be ensured.
• Solution:
  • Use sleep and wakeup to move processes from running to waiting state and waiting to ready state.
  • Maintain a queue of processes waiting and wake up processes in that order.

class semaphore { private: int value; list<PCB> wait_list; public: semaphore() { value = 0; wait_list = list<PCB>(); } semaphore(int a) { value = a; wait_list = list<PCB>(); }	void wait(void) { value--; if (value < 0) { wait_list.push_front( current); sleep(); } } void signal(void) { PCB p; value++; if (value <=0) { p = *(wait_list.end()); wait_list.pop_back(); wakeup(p); } } }