ACE/examples/Smart_Pointers/Widget_Part_Impl.cpp

   1 /* -*- C++ -*- */
   2 //=============================================================================
   3 /**
   4  *  @file    Widget_Part_Impl.cpp
   5  *
   6  *  @author Christopher Kohlhoff <chris@kohlhoff.com>
   7  */
   8 //=============================================================================
   9
  10 #include "Widget_Part_Impl.h"
  11 #include "ace/ACE.h"
  12 #include "ace/Log_Msg.h"
  13 #include "ace/Refcounted_Auto_Ptr.h"
  14 #include "ace/Unbounded_Queue.h"
  15 #include "ace/Null_Mutex.h"
  16
  17 Widget_Part_Impl::Widget_Part_Impl (Widget *owner, const char* name, int size)
  18   : owner_ (owner),
  19     name_ (ACE::strnew (name)),
  20     size_ (size)
  21 {
  22   ACE_DEBUG ((LM_DEBUG, "Widget_Part_Impl constructor\n"));
  23 }
  24
  25 Widget_Part_Impl::~Widget_Part_Impl ()
  26 {
  27   ACE_DEBUG ((LM_DEBUG, "Widget_Part_Impl destructor\n"));
  28
  29   delete [] name_;
  30 }
  31
  32 void Widget_Part_Impl::print_info ()
  33 {
  34   ACE_DEBUG ((LM_INFO, "Widget part: name=%s size=%d\n", name_, size_));
  35 }
  36
  37 void Widget_Part_Impl::remove_from_owner ()
  38 {
  39   // Since we only have a raw pointer to refer to the owner, we have no way of
  40   // checking whether the owner still exists, and if it does guaranteeing that
  41   // it will continue to exist for the duration of this call. This is not an
  42   // issue in this limited example program, but in multithreaded applications
  43   // this function may be called from a different thread to that managing the
  44   // lifetime of the owner object. See the Gadget example for how
  45   // ACE_Strong_Bound_Ptr/ACE_Weak_Bound_Ptr can be used to address the problem.
  46
  47   // Take all existing parts from the owner and build up a temporary queue. If
  48   // we find ourselves then we won't add ourselves to the queue. We will
  49   // actually store ACE_Refcounted_Auto_Ptr instances in the queue, and since we
  50   // know that there is only one thread involved we can use ACE_Null_Mutex to
  51   // eliminate the locking overhead.
  52   ACE_Unbounded_Queue<ACE_Refcounted_Auto_Ptr<Widget_Part, ACE_Null_Mutex> > parts;
  53   for (;;)
  54     {
  55       ACE_Refcounted_Auto_Ptr<Widget_Part, ACE_Null_Mutex> part (owner_->remove_part ());
  56       if (part.null ())
  57         break;
  58       if (part.get () == this)
  59         // Someone else will be responsible for our lifetime.
  60         part.release();
  61       else
  62         parts.enqueue_tail (part);
  63     }
  64
  65   // Add the remaining parts back to the gadget.
  66   while (!parts.is_empty ())
  67     {
  68       ACE_Refcounted_Auto_Ptr<Widget_Part, ACE_Null_Mutex> part;
  69       parts.dequeue_head (part);
  70       owner_->add_part (part.release ());
  71     }
  72 }