Kernel Objects and Watchers

Semaphore

Semaphore are important in the concept of kernel objects and watchers. There main purpose is thread blocking. In order to wake unblock a thread the blocker either needs to be interrupted or receive a signal. This signal is not the same as a signal used in LIBC.

Basic Semaphore Blocker Definition:

class SemaphoreBlocker : public ThreadBlocker{
        friend class Semaphore;
    public:
        SemaphoreBlocker* next = nullptr;
        SemaphoreBlocker* prev = nullptr;
  
        Semaphore* semaphore = nullptr;
  
        inline SemaphoreBlocker(Semaphore* sema) : semaphore(sema) {
  
        }
  
        void Interrupt(){
            interrupted = true;
            shouldBlock = false;

            acquireLock(&lock);
            if(semaphore){
                semaphore->blocked.remove(this);

                semaphore = nullptr;
            }

            if(thread){
                thread->Unblock();
            }
            thread = nullptr;
            releaseLock(&lock);
        }

        void Unblock(){
            shouldBlock = false;

            acquireLock(&lock);
            if(semaphore){
                semaphore->blocked.remove(this);
            }
            semaphore = nullptr;

            if(thread){
                thread->Unblock();
            }
            releaseLock(&lock);
        }
        ~SemaphoreBlocker(){
            if(semaphore){
                semaphore->blocked.remove(this);
            }
        }
    };

Currently the main use of a semaphore is to aid in the Syscall Sleep function as it can block a thread from running. And also to await for a reply from a message.

Kernel Objects

A kernel object is a object that is used towards Processes. This can be MessageEnpoints, Interfaces, Services or Processes themselves.

Processes can watch other processes.