Effective C + + clause 14: Careful copying of behavior in resource management classes

Attention:

• The assignment Raii object must replicate the resources it manages, so the copy behavior of the resource determines the copy behavior of the Raii object.
• General and common RAII copy behavior is: Suppress the copy, the implementation of reference counting method.

 void  lock  (Mutex* PM);  void  unlock (mutex* class   lock{ public  :  explicit   Lock (Mutex* lock   (MUTEXPTR); }  ~lock () {unlock (mutexptr);}  private  : Mutex  * mutexptr;}; Mutex m;..    {Lock ml ( &m); ...}  //  at the end of the block, automatically unlock the lock  

Lock ML1 (&m);
Lock ML2 (ML1); What happens when you copy Ml1 to ML2?

Solutions
1. Disable copying and define the copy operation as private.

2. Use the reference notation. Here you can use the compiler-generated default destructor, which automatically calls destructors for non-static member variables (in this case, mutexptr). Mutexptr's destructor automatically calls the Tr1::shared_ptr's delete (in this case, unlock) when the reference count is 0.

class Lock {public:    Explicit Lock (mutex* pm)      : mutexptr (PM, unlock)    {         Lock (Mutexptr. Get ();)    } Private :    std::tr1::shared_ptr<Mutex> mutexptr;}

Effective C + + clause 14: Careful copying of behavior in resource management classes