Interrupts and Interrupt Vectors

  
Figure:

• When device generates interrupt, it also generates the vector number to identify itself.
• Trap instruction = software interrupt
• Kernel sets up vector table of interrupt handlers
• Current PC and PSW = onto stack
• New PC and PSW loaded from vector table

if all interrupt handling in assembly language, in the Kernel, then interrupt handlers :

• Save and restore interrupted programs context
• Perform device independent processing

Hence, no software FLIH

Note : Interrupt handlers should however be written in a high level language, and be part of device handler process - particularly valid for real time systems.
Also, LIH in kernel to perform actions common to all interrupt handling.

Note: There is a slight distinction between forking a thread as opposed to forking a process (unix 'fork'). A Unix fork creates a new process, so it has to create a new address space, in addition to a new thread.

Forking a thread is very much like an asynchronous procedure call, it means - go do this work - where the calling thread does not wait for the callee to complete.

What if the calling thread needs to wait ?

Thread Join - wait for a forked thread to finish.

Hence, a traditional procedure call (in Pascal for instance) :

 procedure A()
   B()
 procedure B()

	equivalent to 

  procedure A()
  Thread t = new Thread ;
  t^Fork(B) ; t^Join()

  
Figure: