Prolog system internal predicates

Author(s): Manuel Carro, Daniel Cabeza, Mats Carlsson.

Version: 1.10#7 (2006/4/26, 19:22:13 CEST)

Version of last change: 1.9#92 (2003/7/24, 8:4:39 CEST)

This module implements some miscellaneous predicates which provide access to some internal statistics, special properties of the predicates, etc.

• Usage and interface (prolog_sys)
• Documentation on exports (prolog_sys)
• Documentation on internals (prolog_sys)
• Known bugs and planned improvements (prolog_sys)

Usage and interface (prolog_sys)

Documentation on exports (prolog_sys)

PREDICATE: statistics/0:

Usage:

• Description: Prints statistics about the system.

PREDICATE: statistics/2:

Usage 1: statistics(Time_option, Time_result)

• Description: Gather information about time (either process time or wall time) since last consult or since start of program. Results are returned in milliseconds.
• The following properties should hold at call time: Options to get information about execution time. Time_option must be one of runtime, walltime. (prolog_sys:time_option/1) Time_result is any term. (basic_props:term/1)
• The following properties hold upon exit: Options to get information about execution time. Time_option must be one of runtime, walltime. (prolog_sys:time_option/1) Time_result is a two-element list of integers. The first integer is the time since the start of the execution; the second integer is the time since the previous consult to time. (prolog_sys:time_result/1)

Usage 2: statistics(Memory_option, Memory_result)

• Description: Gather information about memory consumption.
• The following properties should hold at call time: Options to get information about memory usage. (prolog_sys:memory_option/1) Memory_result is any term. (basic_props:term/1)
• The following properties hold upon exit: Options to get information about memory usage. (prolog_sys:memory_option/1) Result is a two-element list of integers. The first element is the space taken up by the option selected, measured in bytes; the second integer is zero for program space (which grows as necessary), and the amount of free space otherwise. (prolog_sys:memory_result/1)

Usage 3: statistics(Garbage_collection_option, Gc_result)

• Description: Gather information about garbage collection.
• The following properties should hold at call time: Options to get information about garbage collection. (prolog_sys:garbage_collection_option/1) Gc_result is any term. (basic_props:term/1)
• The following properties hold upon exit: Options to get information about garbage collection. (prolog_sys:garbage_collection_option/1) Gc_result is a tree-element list of integers, related to garbage collection and memory management. When stack_shifts is selected, the first one is the number of shifts (reallocations) of the local stack; the second is the number of shifts of the trail, and the third is the time spent in these shifts. When garbage_collection is selected, the numbers are, respectively, the number of garbage collections performed, the number of bytes freed, and the time spent in garbage collection. (prolog_sys:gc_result/1)

Usage 4: statistics(Symbol_option, Symbol_result)

• Description: Gather information about number of symbols and predicates.
• The following properties should hold at call time: Option to get information about the number of symbols in the program. (prolog_sys:symbol_option/1) Symbol_result is any term. (basic_props:term/1)
• The following properties hold upon exit: Option to get information about the number of symbols in the program. (prolog_sys:symbol_option/1) Symbol_result is a two-element list of integers. The first one is the number of atom, functor, and predicate names in the symbol table. The second is the number of predicates known to be defined (although maybe without clauses). (prolog_sys:symbol_result/1)

Usage 5: statistics(Option, ?term)

• Description: If Option is unbound, it is bound to the values on the other cases.

PREDICATE: predicate_property/2:

Usage: predicate_property(Head, Property)

• Description: The predicate with clause Head is Property.
• The following properties should hold at call time: Head is any term. (basic_props:term/1) Property is any term. (basic_props:term/1)
• The following properties hold upon exit: Head is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1) Property is an atom. (basic_props:atm/1)

PREDICATE: current_atom/1:

Usage: current_atom(Atom)

• Description: Enumerates on backtracking all the existing atoms in the system.
• The following properties should hold at call time: Atom is a free variable. (term_typing:var/1)
• The following properties hold upon exit: Atom is an atom. (basic_props:atm/1)

PREDICATE: garbage_collect/0:

Usage:

• Description: Forces garbage collection when called.

PREDICATE: new_atom/1:

Usage: new_atom(Atom)

• Description: Returns, on success, a new atom, not existing before in the system. The entry argument must be a variable. The idea behind this atom generation is to provide a fast source of identifiers for new objects, concurrent predicates, etc. on the fly.
• The following properties should hold at call time: Atom is a free variable. (term_typing:var/1)
• The following properties hold upon exit: Atom is an atom. (basic_props:atm/1)

Documentation on internals (prolog_sys)

REGTYPE: time_option/1:

Usage: time_option(M)

• Description: Options to get information about execution time. M must be one of runtime, walltime.

REGTYPE: memory_option/1:

Usage: memory_option(M)

• Description: Options to get information about memory usage.

REGTYPE: garbage_collection_option/1:

Usage: garbage_collection_option(M)

• Description: Options to get information about garbage collection.

REGTYPE: symbol_option/1:

Usage: symbol_option(M)

• Description: Option to get information about the number of symbols in the program.

REGTYPE: time_result/1:

Usage: time_result(Result)

• Description: Result is a two-element list of integers. The first integer is the time since the start of the execution; the second integer is the time since the previous consult to time.

REGTYPE: memory_result/1:

Usage: memory_result(Result)

• Description: Result is a two-element list of integers. The first element is the space taken up by the option selected, measured in bytes; the second integer is zero for program space (which grows as necessary), and the amount of free space otherwise.

REGTYPE: gc_result/1:

Usage: gc_result(Result)

• Description: Result is a tree-element list of integers, related to garbage collection and memory management. When stack_shifts is selected, the first one is the number of shifts (reallocations) of the local stack; the second is the number of shifts of the trail, and the third is the time spent in these shifts. When garbage_collection is selected, the numbers are, respectively, the number of garbage collections performed, the number of bytes freed, and the time spent in garbage collection.

REGTYPE: symbol_result/1:

Usage: symbol_result(Result)

• Description: Result is a two-element list of integers. The first one is the number of atom, functor, and predicate names in the symbol table. The second is the number of predicates known to be defined (although maybe without clauses).

Known bugs and planned improvements (prolog_sys)

• The space used by the process is not measured here: process data, code, and stack also take up memory. The memory reported for atoms is not what is actually used, but the space used up by the hash table (which is enlarged as needed).

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