Skip to main content

How to Killi an Object Prematurely..

Sometimes, you need to force an object to destroy itself because its destructor performs an operation needed immediately. For example, when you want to release a mutex or close a file:

void func(Modem& modem)
{
Mutex mtx(modem); // lock modem
Dial("1234567");
/* at this point, you want to release the
modem lock by invoking Mutex's dtor */
do_other_stuff(); //modem is still locked
} //Mutex dtor called here
After the function Dial() has finished, the modem no longer needs to be locked. However, the Mutex object will release it only when func() exits, and in the meantime, other users will not be able to use the modem. Before you suggest to invoke the destructor explicitly, remember that the destructor will be called once again when func() exits, with undefined behavior:

void func(Modem& modem)
{
Mutex mtx(modem); // lock modem
Dial("1234567");
mtx->~Mutex(); // very bad idea!
do_other_stuff();
} //Mutex dtor called here for the second time
There is a simple and safe solution to this. You wrap the critical code in braces:

void func(Modem& modem)
{
{
Mutex mtx(modem); // lock modem
Dial("1234567");
} //mtx destroyed here
//modem is not locked anymore
do_some_other_stuff();
}
Labels:

Comments

Post a Comment

Popular posts from this blog

MFC - Microsoft Foundation Classes Design Patterns

1 Introduction This paper describes the use of object-oriented software design patterns, as presented in Design Patterns: Elements of Reusable Object-Oriented Software by Gamma et al., within the Microsoft Foundation Class Library (MFC). MFC is used for implementing applications for Microsoft Windows operating systems. Because of the size of the MFC library, a complete analysis would have been beyond the scope of this assignment. Instead, we identified various possible locations for design patterns, using the class hierachy diagram of MFC, and studied the source carefully at these locations. When we did not find a pattern where we expected one, we have documented it anyway, with examples of how the particular problem could have been solved differently, perhaps more elegantly, using design patterns. We have included a brief introduction to MFC in Section 2 , as background information. The analysis has been split into three parts, with one section for each major design pattern ca...
1 comment
Read more

Explain Polymorphism and Flavors of Polymorphism...

Polymorphism is the ability of different objects to react in an individual manner to the same message. This notion was imported from natural languages. For example, the verb "to close" means different things when applied to different objects. Closing a door, closing a bank account, or closing a program's window are all different actions; their exact meaning is determined by the object on which the action is performed. Most object-oriented languages implement polymorphism only in the form of virtual functions. But C++ has two more mechanisms of static (meaning: compile-time) polymorphism: Operator overloading. Applying the += operator to integers or string objects, for example, is interpreted by each of these objects in an individual manner. Obviously, the underlying implementation of += differs in every type. Yet, intuitively, we can predict what results are. Templates. A vector of integers, for example, reacts differently from a vector of string objects when it receives ...
17 comments
Read more

• Why might you need exception handling be used in the constructor when memory allocation is involved?

Your first reaction should be: "Never use memory allocation in the constructor." Create a separate initialization function to do the job. You cannot return from the constructor and this is the reason you may have to use exception handling mechanism to process the memory allocation errors. You should clean up whatever objects and memory allocations you have made prior to throwing the exception, but throwing an exception from constructor may be tricky, because memory has already been allocated and there is no simple way to clean up the memory within the constructor.
Post a Comment
Read more