1. Set the Prolog flag exit_status to Status.

2. Call all hooks registered using at_halt/1. If Status equals 0 (zero), any of these hooks calls cancel_halt/1, termination is cancelled.

3. Call all hooks registered using PL_at_halt(). In the future, if any of these hooks returns non-zero, termination will be cancelled. Currently, this only prints a warning.

4. Perform the following system cleanup actions:
   • Cancel all threads, calling thread_at_exit/1 registered termination hooks. Threads not responding within 1 second are cancelled forcefully.
   • Flush I/O and close all streams except for standard I/O.
   • Reset the terminal if its properties were changed.
   • Remove temporary files and incomplete compilation output.
   • Reclaim memory.

5. Call exit(Status) to terminate the process

halt/1 has been extended in SWI-Prolog to accept the arg abort. This performs as halt/1 above except that:

• Termination cannot be cancelled with cancel_halt/1.
• abort() is called instead of exit(Status).