Re: [boost] Non-thread-safe thread library (Boost.Function)

From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2007-12-19 17:25:20

Douglas Gregor wrote:
> Phil Endecott wrote:
>> - What exactly is the race between?  E.g. if I know that I'll never 
>> create two threads at the same time, do I still need to worry about 
>> other uses of Boost.Function that may be concurrent?  Is the race 
>> between creating the function objects or between using them, or both?
>
> The race will occur if you construct or assign to two boost::function 
> objects:
>      - that have the same type, and
>     - with target function objects of the same type, and
>     - you have never completely constructed/assigned to a 
> boost::function object of that type with that target function object type

OK, so the common case where I have a main thread that spawns 
per-operation threads:

void handle_request(request_t req) { .... }
void main() {
   while (1) {
     request_t r = receive_request();
     thread t(bind(handle_request,r));
   }
}

is safe, if this is the only place where threads are created.  Another 
common case in my code is a per-object thread:

class C {
   void run() { .... }
   thread run_thread;
public:
   C():
     run_thread(bind(C::run,this))
   {}
   ~C() { run_thread.join(); }
};

Because C is in the type, I only need to worry about concurrent 
creation of C objects; there's no race with threads in other classes.

>> - Can I avoid the problem by using a new version of Boost.Function, 
>> without upgrading other libraries?  (Is Boost.Function header-only?)

[No, because]
> You should recompile anything that depends on Function (e.g., the threads 
> library)

> This should have gone on the web page, at the very least, and I'll do so 
> now.

Thanks.

Phil.