Re: [Boost-users] why is make_shared using so much of my stack....?

Subject: Re: [Boost-users] why is make_shared using so much of my stack....?
From: Jeff Flinn (TriumphSprint2000_at_[hidden])
Date: 2011-02-05 21:47:08

Michael Xu wrote:
> Hi everyone,
> 
> I've been investigating our program's memory usage, and one of the spots 
> that I keep seeing the stack hitting its limit is when using 
> boost::make_shared. 
> 
> I've written a simple test program, that completes fine when I use 
> new... but fails with a stack overflow when I use boost::make_shared
> ========================
> #include <iostream>
> #include <boost/shared_ptr.hpp>
> #include <boost/make_shared.hpp>
> using namespace std;
> struct  arr
> {
> char arg[1024*1024];
> };
> 
> struct test
> {
> struct arr array[1024];
> };
> 
> int main()
> {
> test * myTest = new test(); //complete! 
> if (!myTest)
> cout << "new alloc failed";
> boost::shared_ptr<test> testPtr = boost::make_shared<test>(); //fails 
> with stack overflow!
> if (!testPtr)
> {
> cout << "alloc failed;";
> }
> }
> ===========================
> 
> If you run this with a reasonable thread stack of 8 megabytes, it fails 
> when using boost::make_shared.
> 
> Here is the stack trace..... 
> 
> #0  boost::shared_ptr<test>::shared_ptr<test, 
> boost::detail::sp_ms_deleter<test> >(test*, 
> boost::detail::sp_ms_deleter<test>) ()
> #1  boost::shared_ptr<test> boost::make_shared<test>() ()
> #2  main ()
> 
> 
> Is there a reason this happens?

Do you mean heap rather than stack?

You are first allocating with new:

1024 * 1024 * 1024 = 1,073,741,824 = 1GB of contiguous memory.

Then your attempting to allocate another 1GB with make_shared. This has 
a good chance of failing on 32bit windows systems. You don't mention the 
OS.

I would expect that make_shared is throwing an exception like 
std::bad_alloc which you are not cathing.

Jeff