1b0ac538   
   From: josephgottman@comcast.net   
      
   On 11/11/2011 8:30 AM, Nikolay Ivchenkov wrote:   
   > C++11 - 30.4.4.2 provides the following declaration of std::call_once:   
   >   
   >      template   
   >          void call_once(   
   >              once_flag&  flag,   
   >              Callable&&  func,   
   >              Args&&... args);   
   >   
   > According to 30.4.4.2/2,   
   >   
   >      An execution of call_once that calls its func is an active   
   > execution. An active execution shall call INVOKE(DECAY_COPY   
   > ( std::forward(func)), DECAY_COPY   
   > (std::forward(args))...).   
   >   
   > What is the point in using decay_copy here? Why can't an active   
   > execution just call   
   >   
   >      INVOKE(std::forward(func), std::forward(args)...)   
   >   
   > ?   
   >   
   >   
      
      Most of the functions in the threading library call DECAY_COPY so   
   that they have unique copies of all their parameters.  They start new   
   threads, so they need to have all their parameters to be unshared to   
   avoid race conditions.  call_once is called in the current thread, so   
   this doesn't apply, but it is probably called like the others for   
   consistency.   
      
   Joe Gottman   
      
      
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