Re: stdext::hash_map

"mlimber" <>
6 Jun 2006 08:39:41 -0700
Dymus wrote:

problem with deleting big sized hash_map.
have defined a comporator, where defined min_bucket_size (for speed
improvement, since i know that i need to store big ammount of data
(~1Mln)), everything seems to be good, working fast, but problems start
when try to .clear() or delete that hash_map... I think that it just
take ennormous amount of time to complete this thing. Waiting for
possible suggestions for solvation of this problem

Define "enormous amount of time." 2 seconds, 30 minutes, a week? What
happens if you allocate 1 million separate chunks of memory the same
size as one key/value pair in your hash table and then try to delete
them all? Here's a simpler case: How long does the last line of the
following take?

#include <list>

// Substitute your value and key types here
struct MyData { int key; int value[ 3 ]; };

 void Foo()
   std::list< MyData > lst;
   for( unsigned i=0; i < 1000000U; ++i )
     lst.push_back( MyData() );

   // Swap trick to clear and get rid of capacity, too
   std::list<MyData>().swap( lst );

It might just be that it takes a while to free that much memory when
allocated separately since it is O( N ) to delete.

Cheers! --M

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