Re: garbage collection

[Elmar Haneke]

> (2) How much of a problem is this in practice?  What kind of programming
> constructs lead to running out of memory?

You easyly can run out of space or allocate lots of memory on large jobs.

I yust did an small test on prime number calculation, the executable 
produced by gprolog dod allocate 17times more memory than the 
equivalent algorithm compiled with "Mercury" which uses (besides other 
options) the Boehm Collector.

Elmar

======================= primes.pl ================================

extract([H|Tail1],Div,Tail2):-
        0 is H mod Div,
        extract(Tail1,Div,Tail2).
extract([H|Tail1],Div,[H|Tail2]):-
        H mod Div > 0,
        extract(Tail1,Div,Tail2).
extract([],_,[]).
                        
sieve([H|Tail],[H|List]):-
        extract(Tail,H,L),
        sieve(L,List).
sieve([],[]).

numbers(Max,Max,[Max]).
numbers(Min,Max,[Min|List]):-
        Min<Max,
        Min2 is Min+1,
        numbers(Min2,Max,List).

prime_numbers(Max,List) :-
        numbers(2,Max,All),
        sieve(All,List).

q :- print('start'),nl,
     prime_numbers(60000,X),
     length(X,L),write(L),nl
     .

:- initialization(q).

===================== execute ===========================
/usr/bin/time -v ./m_primes
6057
        Command being timed: "./m_primes"
        User time (seconds): 1.96
        System time (seconds): 0.06
        Percent of CPU this job got: 82%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:02.47
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 0
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 2205
        Voluntary context switches: 1
        Involuntary context switches: 3582
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0

address@hidden:~/mydata/mercury$ /usr/bin/time -v ./p_primes
start
6057
        Command being timed: "./p_primes"
        User time (seconds): 6.48
        System time (seconds): 0.15
        Percent of CPU this job got: 94%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:07.06
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 0
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 117
        Minor (reclaiming a frame) page faults: 37318
        Voluntary context switches: 120
        Involuntary context switches: 2120
        Swaps: 0
        File system inputs: 0
        File system outputs: 0
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0