Release stack memory resources that are not in use at this moment,
returning them to the operating system. It can be used to release memory
resources in a backtracking loop, where the iterations require typically
seconds of execution time and very different, potentially large, amounts
of stack space. Such a loop can be written as follows:
loop :-
generator,
trim_stacks,
potentially_expensive_operation,
stop_condition, !.
The Prolog top-level loop is written this way, reclaiming memory
resources after every user query.
Set a parameter for one of the Prolog runtime stacks. Stack
is one of local, global, trail or argument.
The table below describes the Key(Value) pairs. Value
can be an arithmetic integer expression. For example, to specify a 2 GB
limit for the global stack, one can use:
?- set_prolog_stack(global, limit(2*10**9)).
Current settings can be retrieved with prolog_stack_property/2.
- limit(+Bytes)
-
Set the limit to which the stack is allowed to grow. If the specified
value is lower than the current usage a
permission_error is
raised. If the limit is larger than supported, the system silently
reduces the requested limit to the system limit.
- min_free(+Cells)
-
Minimum amount of free space after trimming or shifting the stack.
Setting this value higher can reduce the number of garbage collections
and stack-shifts at the cost of higher memory usage. The spare stack
amount is reported and specified in `cells'. A cell is 4 bytes in the
32-bit version and 8 bytes on the 64-bit version. See
address_bits.
See also trim_stacks/0
and debug/0.
- spare(+Cells)
-
All stacks trigger overflow before actually reaching the limit, so the
resulting error can be handled gracefully. The spare stack is used for
print_message/2
from the garbage collector and for handling exceptions. The default
suffices, unless the user redefines related hooks. Do
not specify large values for this because it reduces the amount
of memory available for your real task.
Related hooks are message_hook/3
(redefining GC messages),
prolog_trace_interception/4
and prolog_exception_hook/4.
