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

19 Dec 2007

      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.