Re: [boost] Memoryleaks in boost::pool_allocator

From: Paul Bormans (pbor1234_at_[hidden])
Date: 2008-08-27 14:46:24

Dean Michael,
I've just ran with purge_memory as well, and much to my surprise, all memory gets free then... Documentation explains that purge_memory invalidates each pointer to that block (while release_memory does only free memory that is no longer referenced) which makes me believe that there is a ref-leak of some kind. The memory cannot be referenced any more since the vector is out of scope, right?
 
Even though purge_memory releases all memory previously allocated, i still see a problem in a scenario where the (singleton) pool is used, then purged/released frequently, it will quickly run out of memory, as shown below in the sample.
 
To my opinion, the release_memory doesn't do what it is supposed to do and in addition i have doubts if the size of the next block is correct.
 
What would be the best way to get this solved? (as i'm only a boost user and not a developer (yet ;))?
 
In code with some results added in comments:
 
....continued from previous tests (see original post)....
std::pair<int, int> pairInterim4(m_spLeakDetection->ReportLeaks(_T("boost test 2d"))); //still 16312 bytes over 7 blocks
boost::singleton_pool<boost::pool_allocator_tag, sizeof(int)>::release_memory();
std::pair<int, int> pairInterim5(m_spLeakDetection->ReportLeaks(_T("boost test 2e1"))); //8112 over 6 blocks; 136, 264, 520, 1032, 2056, 4104
boost::singleton_pool<boost::pool_allocator_tag, sizeof(int)>::purge_memory();
std::pair<int, int> pairEnd(m_spLeakDetection->ReportLeaks(_T("boost test 2e2"))); //0 bytes
{
  std::vector<int, boost::pool_allocator<int> > v;
  for (int i = 0; i < 10; ++i) { v.push_back(5); }
  std::pair<int, int> pairInterim3(m_spLeakDetection->ReportLeaks(_T("boost test 2f"))); //16392 bytes over 1 block
  v.clear();
}
for(int count=0; count<15; ++count)
{
  {
    std::vector<int, boost::pool_allocator<int> > v;
    for (int i = 0; i < 1000; ++i) { v.push_back(5); }
    std::pair<int, int> pairTest1(m_spLeakDetection->ReportLeaks(_T("boost test 2x1"))); //giving 16392, 32776, ..... 268435464
    v.clear();
    boost::singleton_pool<boost::pool_allocator_tag, sizeof(int)>::release_memory();
  }
  boost::singleton_pool<boost::pool_allocator_tag, sizeof(int)>::purge_memory();
  std::pair<int, int> pairTest2(m_spLeakDetection->ReportLeaks(_T("boost test 2x2")));
}
 

> Date: Wed, 27 Aug 2008 16:49:51 +0800> From: mikhailberis_at_[hidden]> To: boost_at_[hidden]> Subject: Re: [boost] Memoryleaks in boost::pool_allocator> > Hi Paul,> > On Wed, Aug 27, 2008 at 2:44 AM, Paul Bormans <pbor1234_at_[hidden]> wrote:> > Some time ago i had noticed some strange behavior in the boost pool_allocator regarding its memory usage. Now that i've found these great mailinglists ;) i've reproduced the error and with some additional analysis i can post the thing here.> >> > I have the same experience, although with Linux and GCC 4.1.2. More precisely:> > [snip]> >> > >From these tests;> > - why does the boost::pool_allocator reserve 16312 bytes for 1000 int's while the default stl vector consumes (only) 4264 bytes?> > I think it has something to do with the way the pool_allocator grows,> which is by doubling the available pool source every time it "runs out> of available free contiguous space".> > > - why does a call to release_memory( ) not remove all the memory allocations done by the pool_allocator? But only the last block?> > I think this is the major bug that gets exacerbated in "high data> churn applications" -- where lots of small containers acquire/release> memory often, and the pool_allocator just doesn't know about the> blocks that are supposedly "free" and "available" again.> > > - why does the size of each new block gets duplicated in size (even after release_memory)?> >> > This I think is the intended behavior (which I think you mean is that> the size of the whole memory block gets doubled every time).> > > Does this make sense to any of you?> > No, but it would be nice to know if indeed this is a bug and whether> there should be additional tests to expose the bug.> > One thing I notice is that there's an interface to> pool_allocator<...>::purge_memory() -- or something similar. Is this> by any means part of the standard allocator interface and shouldn't> this be called whenever a release is called as well?> > HTH> > -- > Dean Michael C. Berris> Software Engineer, Friendster, Inc.> _______________________________________________> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
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