Oddity with memory manglement in 5.8.8, 5.10.0

lembark has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Oddity with memory manglement in 5.8.8, 5.10.0 by dave_the_m (Monsignor) on Jan 30, 2008 at 08:48 UTC
This is a well-known problem with depply-recursive data structures. The code in perl to free such structures is recursive, and after a cetain depth it blows the processor stack. The workarounds are to increase the stack size with ulimit, or free the struture using perl-level recursion (which doesn't use the stack). Dave.	[reply]
Re: Oddity with memory manglement in 5.8.8, 5.10.0 by ysth (Canon) on Jan 30, 2008 at 02:56 UTC
Your example code is very odd; it is equivalent to just `$node = [[],@data]` except that it has a side effect on the array originally referred to by $node (if there was one). Please do show your actual code, and tell more about this "message from DESTROY"? -- Online Fortune Cookie Search	[reply] [d/l]
Re: Oddity with memory manglement in 5.8.8, 5.10.0 by rjray (Chaplain) on Jan 30, 2008 at 01:43 UTC
Can you provide a relatively small test-script that exhibits the problem? Something one of us can run under the debugger and/or a source-level debugger? `--rjray`	[reply]
Re: Oddity with memory manglement in 5.8.8, 5.10.0 by lembark (Novice) on Jan 30, 2008 at 15:34 UTC
I figured it was a known issue, thanks. Annoyance is that that the thing doesn't have to be recursive, guess I have to use a skip list to destroy the thing in chunks. The code for tesing this and finding the limit is trivial: #!/opt/bin/perl use strict; select STDERR; $\| = 1; print "\nCount, Last value:\n"; for my $count ( 215 .. 218) { print "Testing: $count -> "; my $head = []; my $node = $head; ( $node ) = @{ $node } = ( [], $_ ) for 1 .. $count; bless $node, 'TailNode'; my $value = ''; for( $node = $head ; @$node ; ) { ( $node, $value ) = @$node; } print "$value\n"; # $head goes out of scope and segfaults here. } package TailNode; DESTROY { print "Destroying $_[0]\n"; } __END__ Trial runs: Teseting: 37405 -> 37405 Destroying TailNode=ARRAY(0x82d7f40) Teseting: 37406 -> 37406 Destroying TailNode=ARRAY(0x83425b0) Teseting: 37407 -> 37407 Segmentation fault [download]	[reply] [d/l]
Re^2: Oddity with memory manglement in 5.8.8, 5.10.0 by almut (Canon) on Jan 30, 2008 at 17:49 UTC
...the thing doesn't have to be recursive The issue is that while running your code, perl internally builds up a call stack of impressive depth (218255 frames here — my attempt segfaulted at `$count` being around 43650 (with the default `ulimit -s` setting of 8192kB)), as shown by the backtrace based on the core dump: $ ./665040.pl Count, Last value: Testing: 43650 -> 43650 Segmentation fault (core dumped) $ gdb /usr/local/perl/5.10.0/bin/perl core (...) Core was generated by `/usr/local/perl/5.10.0/bin/perl ./665040.pl'. Program terminated with signal 11, Segmentation fault. #0 0x080acd57 in Perl_sv_clear () (gdb) bt #0 0x080acd57 in Perl_sv_clear () #1 0x080ad378 in Perl_sv_free2 () #2 0x0809915f in Perl_av_undef () #3 0x080ad129 in Perl_sv_clear () #4 0x080ad378 in Perl_sv_free2 () #5 0x080acd5f in Perl_sv_clear () #6 0x080ad378 in Perl_sv_free2 () (...) (...) #218242 0x0809915f in Perl_av_undef () #218243 0x080ad129 in Perl_sv_clear () #218244 0x080ad378 in Perl_sv_free2 () #218245 0x080acd5f in Perl_sv_clear () #218246 0x080ad378 in Perl_sv_free2 () #218247 0x0809915f in Perl_av_undef () #218248 0x080ad129 in Perl_sv_clear () #218249 0x080ad378 in Perl_sv_free2 () #218250 0x080c79e0 in Perl_leave_scope () #218251 0x080a13a8 in Perl_pp_unstack () #218252 0x080a0bb8 in Perl_runops_standard () #218253 0x0809f652 in perl_run () #218254 0x0805ee8f in main () (gdb) [download]	[reply] [d/l] [select]
Re: Oddity with memory manglement in 5.8.8, 5.10.0 by lembark (Novice) on Jan 30, 2008 at 18:04 UTC
Fortunately the fix is simple and runs quickly enough: iterate the destruction. thanks again for the info. `Testing: 131093 Construct: 0.195811033248901 669487 Hz Walk: 0.0962779521942139 1361609 Hz Destroy: 0.0676219463348389 1938616 Hz` [download] `DESTROY { my $head = shift; $head = delete $head->[0] while $head; }` [download]	[reply] [d/l] [select]