18 Limiting process resources
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Availability::- use_module(library(rlimit)).(can be autoloaded)
rlimit(+Resource, -Old, +New)
Query and/or set the limit for Resource. Time-values are in seconds and size-values are counted in bytes. The following values are supported by this library. Please note that not all resources may be available and accessible on all platforms. This predicate can throw a variety of exceptions. In portable code this should be guarded with catch/3. The defined resources are:
as Max address space
cpu CPU time in seconds
fsize Maximum filesize
data max data size
stack max stack size
core max core file size
rss max resident set size
nproc max number of processes
nofile max number of open files
memlock max locked-in-memory address

When the process hits a limit POSIX systems normally send the process a signal that terminates it. These signals may be caught using SWI-Prolog's on_signal/3 primitive. The code below illustrates this behaviour. Please note that asynchronous signal handling is dangerous, especially when using threads. 100% fail-safe operation cannot be guaranteed, but this procedure will inform the user properly‘most of the time'. 

rlimit_demo :-
        rlimit(cpu, _, 2),
        on_signal(xcpu, _, cpu_exceeded),
        ( repeat, fail ).

cpu_exceeded(_Sig) :-
        format(user_error, 'CPU time exceeded~n', []),
        halt(1).