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Paul Bormans | 26 Aug 20:40
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Memoryleaks in boost::pool_allocator

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.

My environment:
- VS2005
- Windows XP
- Boost 1_34_1 with BOOST_ALL_DYN_LINK set (if it makes a difference)
- Running release build

The test code:

  {
    std::pair<int, int> pairStart(m_spLeakDetection->ReportLeaks(_T("boost test 1a")));
    {
      std::vector<int> v;
      std::pair<int, int> pairInterim2(m_spLeakDetection->ReportLeaks(_T("boost test 1b"))); //0 bytes
(only stack memory used)
      for (int i = 0; i < 1000; ++i) { v.push_back(5); }
      std::pair<int, int> pairInterim3(m_spLeakDetection->ReportLeaks(_T("boost test 1c"))); //4264
bytes in 1 block
      v.clear();
    }
    std::pair<int, int> pairInterim4(m_spLeakDetection->ReportLeaks(_T("boost test 1d"))); //0 bytes
  }

  {
    std::pair<int, int> pairStart(m_spLeakDetection->ReportLeaks(_T("boost test 2a")));
    {
      std::vector<int, boost::pool_allocator<int> > v;
(Continue reading)

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Dean Michael Berris | 27 Aug 10:49

Re: Memoryleaks in boost::pool_allocator

Hi Paul,

On Wed, Aug 27, 2008 at 2:44 AM, Paul Bormans <pbor1234 <at> hotmail.com> 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)?
>
(Continue reading)

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Paul Bormans | 27 Aug 20:46
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Re: Memoryleaks in boost::pool_allocator

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
(Continue reading)

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Paul Bormans | 29 Aug 11:28
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Re: [Boost-users] Format local time in W3C format (YYYY-MM-DDThh:mm:ss.sTZD) without providing the time zone myself?

Does anyone have hints/tips for me to get properly formatted time zone (%Q) for local time without
providing the time zone myself?

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