[Boost-bugs] [Boost C++ Libraries] #3658: Remove dependency on static initialization/destruction order

Subject: [Boost-bugs] [Boost C++ Libraries] #3658: Remove dependency on static initialization/destruction order
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-11-23 07:18:37

#3658: Remove dependency on static initialization/destruction order
------------------------------+---------------------------------------------
 Reporter:  andysem           |       Owner:  joaquin  
     Type:  Feature Requests  |      Status:  new      
Milestone:  Boost 1.42.0      |   Component:  flyweight
  Version:  Boost 1.41.0      |    Severity:  Problem  
 Keywords:                    |  
------------------------------+---------------------------------------------
 The static_holder depends on the static initialization/destruction order,
 as it is implemented as a function-local static variable. If there are
 flyweights in the static or global variables, which are initialized
 lazilly, the flyweight value may get destroyed before the flyweights that
 refer to it. For example:

 {{{
 #include <iostream>
 #include <string>
 #include <boost/shared_ptr.hpp>
 #include <boost/flyweight.hpp>
 #include <boost/flyweight/key_value.hpp>

 struct A
 {
         int m_n;

         A(int n) : m_n(n)
         {
                 std::cout << "A()" << std::endl;
         }
         ~A()
         {
                 std::cout << "~A()" << std::endl;
         }

         bool operator== (A const& a) const
         {
                 return m_n == a.m_n;
         }

         friend std::size_t hash_value(A const& a)
         {
                 return a.m_n;
         }
 };

 struct B
 {
         boost::flyweight< boost::flyweights::key_value< int, A > > m_A;

         B() : m_A(10)
         {
                 std::cout << "B()" << std::endl;
         }
         ~B()
         {
                 std::cout << "~B()" << std::endl;
         }
 };

 boost::shared_ptr< B > p;

 int main(int, char*[])
 {
         p.reset(new B());
         return 0;
 }
 }}}

 Compiled with MSVC:

 {{{
 cl -Ox -MD -EHsc -I . -DNDEBUG ./flyweight_test.cpp
 }}}

 Produces:

 {{{
 A()
 B()
 ~A()
 ~B()
 }}}

 And a crash.

 A possible solution would be to destroy flyweight values only when
 reference counter from flyweights drops to zero.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3658>
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