Exceptions, Memory Management, and Concurrency
This question asks you to compare properties of exceptions in C++ and Java.
(a) In C++, objects may be reside in the activation records that are deallocated when an exception is thrown. As these activation records are deallocated, all of the destructors of these stack objects are called. Explain why this is a useful language mechanism.
(b) In Java, objects are allocated on the heap instead of the stack. However, an activation record that is deallocated when an exception is raised may con- tain a pointer to an object. If you were designing Java, would you try to call the ?nalize methods of objects that are accessible in this way? Why or why not?
(c) Brie?y explain one programming situation in which the C++ treatment of objects and exceptions is more convenient than Java and one situation in which Java is more convenient than C++.
(d) In languages that allow programs to contain multiple threads, several threads may be created between the point where an exception handler is established and the point where an exception is thrown. In the spirit of trying to abort any computation that is started between these two points, a programming language might try to abort all such threads when an exception is raised. In other words, there are two possible language designs:
- raising an exception affects only the current thread, or
- raising an exception aborts all threads that were started between the point where the exception handler is established and the point where the exception is thrown.
Which design would be easier to implement? Explain brie?y.
(e) Brie?y explain one programming situation in which you would like raising an exception to abort all threads that were started between the point where the exception handler is established and the point where the exception is thrown. Can you think of a programming situation in which you would prefer not to have these threads terminated?