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School of Computer Science & Engineering
University of New South Wales
 Advanced Operating Systems 
 COMP9242 2002/S2 

Thread Manipulation: lthread_ex_regs System Call

• Task has a fixed number (128) of threads, initially all but one inactive.
• Thread is activated by supplying a valid IP and SP.
  • Thread inherits pager, excepter from activating thread.
• lthread_ex_regs() sets new and returns previous values for
  instruction pointer (IP), stack pointer (SP), exception handler, pager.
• Supplying invalid value (-1) to any of those retains original setting.

  Can be used for:

  • performing a user-level thread switch
    (exchanging registers of running thread with saved ones);
  • saving thread's context (by supplying only invalid parameters).
• Call terminates any pending or ongoing IPC.

Note: A thread cannot be ``deleted'', it is stopped by blocking.