Re: [Boost-users] Thread Safety of shared_ptr

Subject: Re: [Boost-users] Thread Safety of shared_ptr
From: Peter Dimov (pdimov_at_[hidden])
Date: 2011-05-03 08:18:37

Kevin Frey wrote:

> 2.       One thread A creating another shared_ptr to the shared object, 
> attempting to increment the reference count.
>
> 3.       Another thread B simultaneously destroying a *different* 
> shared_ptr which is connected to the same underlying shared object, 
> decrementing the reference count.

This is OK. Manipulating different shared_ptr instances in different threads 
is fine. The example states that you can't, in thread B, destroy the 
shared_ptr which thread A copies (*sp_Session in your code). Destroying 
other shared_ptr instances is allowed, regardless of whether or with what 
they share ownership. The thread safety rules work on shared_ptr instances, 
not on their pointees. You can replace shared_ptr with std::string (or even 
int) in the examples and they will be equally valid (provided that reset is 
replaced with assignment). (Although I admit that the variable names are 
used somewhat loosely.)