Modifying all matching elements in a Boost.MultiIndex Container

Amit Prakash Ambasta

31 Dec 2015 31 Dec '15

3:22 p.m.

Hi, I am trying to modify members of all elements matching value for a given index in a boost.multiindex container index.modify( index.find(value), [](T& element) { ... } ) seems to update a singular element(first match) On the other hand, std::pair iter = index.equal_range(value); while(iter.first != iter.second) { index.modify( iter.first, [](T& element) { ... } ); iter.first++; } leads to segfaults and unexpected behavior. What would be right way to approach this?

Attachments:

attachment.html (text/html — 858 bytes)

Show replies by date

Joaquín M Lopez Munoz

31 Dec 31 Dec

7:33 p.m.

New subject: Modifying all matching elements in a Boost.MultiIndex Container

Amit Prakash Ambasta writes:

...

std::pair iter = index.equal_range(value);

while(iter.first != iter.second) {

index.modify( iter.first, [](T& element) { ... } );

iter.first++; }

leads to segfaults and unexpected behavior.

What would be right way to approach this?

This is a classic, please follow these links for further info: http://stackoverflow.com/questions/29013600/ modifying-key-ranges-in-a-boost-multi-index-map-having-hashed-non-unique-keys http://lists.boost.org/boost-users/2006/03/18048.php Joaquín M López Munoz Telefónica

Amit Prakash Ambasta

8:55 p.m.

New subject: Modifying all matching elements in a Boost.MultiIndex Container

Hey Joaquin First of all, thank you so much for your repeated help. In line with the example provided, I've written a generic find_and_modify function as: template Segment* find_and_modify(T& iterable, F filters, State s, double a_arr=-1, Comment rmk=Comment::INFO_SEGMENT_PREDICTED) { auto iter = iterable.find(filters); if (iter == iterable.end()) return nullptr; std::pair iter_main = iterable.equal_range(filters); while (iter_main.first != iter_main.second) { auto it = boost::multi_index::project<aux>(segment, iter_main.first); segment.get<aux>().modify( it, [&s, &a_arr, &rmk](Segment& seg) { seg.state = s; if (a_arr != -1) seg.a_arr = a_arr; if (rmk != +Comment::INFO_SEGMENT_PREDICTED) { seg.comment = rmk; } } ); iter_main.first++; } return (Segment *)(&(*iter)); } where T is an index on container instance segment as segment.get<sometag>(); This seems to work well for the most part but it still segfaults. Any ideas what I'm doing wrong. As specified in the SO answer, I've created an aux index and projected the current iterator to it so as to not modify the current iterator, and yet on debugging the function, I've found that iter_main.first evaluates to garbage at some point as: (gdb) p (*iter_main.first) $7 = (const boost::multi_index::detail::index_node_base::value_type &) @0x6b3c10: { index = " \252\355\000\000\000\000\000\020\376u\000\000\000\000\000\060\355u\000\000\000\000\000\020\376u\000\000\000\000\000\320\361j\000\000\000\000\000\360:r\000\000\000\000\000\270۾\366\377\177\000\000\270۾\366\377\177\000\000\310۾\366\377\177\000\000\310۾\366\377\177\000\000\330۾\366\377\177\000\000\330۾\366\377\177\000\000\260\363u\000\000\000\000\000\260\363u\000\000\000\000\000`;k\000\000\000\000\000`;k\000\000\000\000\000\200\227j\000\000\000\000\000\200\227j\000\000\000\000\000\030ܾ\366\377\177\000\000\030ܾ\366\377\177\000\000(ܾ\366\377\177\000\000(ܾ\366\377\177\000\000\070ܾ\366\377\177\000\000\070ܾ\366\377\177\000\000Hܾ\366\377\177\000\000"..., code = "OP", cname = "34283", p_arr = 1450614300, p_dep = 1450667229, a_arr = 3, a_dep = inf, t_inb_proc = 3600, t_agg_proc = 0, t_out_proc = 18000, cost = 0, state = {static _size_constant = 5, _value = 3 '\003'}, comment = {static _size_constant = 9, _value = 2 '\002'}, parent = 0x75ed70} On Fri, Jan 1, 2016 at 1:03 AM Joaquín M Lopez Munoz wrote:

...

Amit Prakash Ambasta writes:

...
std::pair iter =

index.equal_range(value);

...
while(iter.first != iter.second) {

index.modify( iter.first, [](T& element) { ... } );

iter.first++; }

leads to segfaults and unexpected behavior.

What would be right way to approach this?

This is a classic, please follow these links for further info:

http://stackoverflow.com/questions/29013600/

modifying-key-ranges-in-a-boost-multi-index-map-having-hashed-non-unique-keys http://lists.boost.org/boost-users/2006/03/18048.php

Joaquín M López Munoz Telefónica _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Joaquin M Lopez Munoz

1 Jan 1 Jan

11:28 a.m.

New subject: Modifying all matching elements in a Boost.MultiIndex Container

Amit Prakash Ambasta writes:

...

Hey Joaquin First of all, thank you so much for your repeated help.

You're welcome. Please don't top post, as suggested by Boost mailing lists guidelines: http://www.boost.org/community/policy.html

...

In line with the example provided, I've written a generic find_and_modify function as:

template Segment* find_and_modify(T& iterable, F filters, State s, double a_arr=-1, Comment rmk=Comment::INFO_SEGMENT_PREDICTED) { auto iter = iterable.find(filters);

if (iter == iterable.end()) return nullptr;

std::pair iter_main = iterable.equal_range(filters);

while (iter_main.first != iter_main.second) { auto it = boost::multi_index::project<aux>( segment, iter_main.first); segment.get<aux>().modify( it, [&s, &a_arr, &rmk](Segment& seg) { seg.state = s; if (a_arr != -1) seg.a_arr = a_arr;

if (rmk != +Comment::INFO_SEGMENT_PREDICTED) { seg.comment = rmk; } } ); iter_main.first++; }

return (Segment *)(&(*iter)); }

where T is an index on container instance segment as segment.get<sometag>();

This seems to work well for the most part but it still segfaults. Any ideas what I'm doing wrong. As specified in the SO answer, I've created an aux index and projected the current iterator to it so as to not modify the current iterator, and yet [...]

This is not helping at all because modify (no matter through which iterator is done) still can change the order of T so that your [iter_main.first,iter_main.second) loop fails. Put another way, the code auto it = boost::multi_index::project<aux>(segment, iter_main.first); segment.get<aux>().modify(it, ...); does exactly the same as T.modify(iter_main.first, ...); The answer in SO works because the loop is over the entire sequence [aux.begin(),aux.end()) (with aux=information_map_.get()), which is stable under modifications of the elements (it's a random-access index). This does not translate well to your scenario, where you need to loop over a subrange [a,b) of the sequence: for it to work [a,b) would have to project to a range [a',b') in the aux index, which of course is not the case (traversal orders are different).

...

I'd also like to point out that your approach via modify_unstable_range as per the boost mailing list works correctly though (however you've commented that it would be a slower approach)

Measure and if performance's OK stick to the modify_unstable_range approach. The aux index technique can be made to work with a little more effort (basically, by rearranging the index with rearrange()) but you might not need to anyway if modify_unstable_range is good enough (and there's no guarantee it's going to be faster to begin with). Joaquín M López Muñoz Telefónica

Amit Prakash Ambasta

31 Dec 31 Dec

9:54 p.m.

New subject: Modifying all matching elements in a Boost.MultiIndex Container

I'd also like to point out that your approach via modify_unstable_range as per the boost mailing list works correctly though (however you've commented that it would be a slower approach) On Fri, Jan 1, 2016 at 1:03 AM Joaquín M Lopez Munoz wrote:

...

Amit Prakash Ambasta writes:

...
std::pair iter =

index.equal_range(value);

...
while(iter.first != iter.second) {

index.modify( iter.first, [](T& element) { ... } );

iter.first++; }

leads to segfaults and unexpected behavior.

What would be right way to approach this?

This is a classic, please follow these links for further info:

http://stackoverflow.com/questions/29013600/

modifying-key-ranges-in-a-boost-multi-index-map-having-hashed-non-unique-keys http://lists.boost.org/boost-users/2006/03/18048.php

Joaquín M López Munoz Telefónica _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

3253

Age (days ago)

3254

Last active (days ago)

List overview

Download

4 comments

3 participants

participants (3)

Amit Prakash Ambasta
Joaquin M Lopez Munoz
Joaquín M Lopez Munoz