Page 318 - DCAP404 _Object Oriented Programming

Unit 14: Advanced Concept in C++

execution will temporarily stop at the breakpoint, before the instruction is executed. The execution Notes
may then be resumed, until the next breakpoint is encountered. Breakpoints are often used in
conjunction with watch values, by observing the current watch value at each breakpoint as the
program executes.

Stepping

Stepping refers to the execution of one instruction at a time, typically by pressing a function key
to execute each instruction. In Turbo C++, for example, stepping can be carried out by pressing
either function keys F7 or F8. ( F8 steps over subordinate functions, whereas F7 steps through the
functions.) By stepping through an entire program, you can determine which instructions produce
erroneous results or generate error messages.

Self Assessment

Fill in the blanks:
9. ......................... objects are objects that are capable of controlling and scheduling the received
before they are served by the object.
10. There are many alternative approaches for introducing concurrency and ......................... is
an object-oriented language.
11. For concurrent object-oriented system ......................... .

14.8 Concurrent Object-oriented Systems

Concurrent objects are objects that exist and operate in the same environment simultaneously.

Our most important goals of object-oriented software development is to construct a model of
the real world. We do this because we want to build a conceptual model, or a description, of the
real world. A closer look at the real world reveals that concurrent activities appear everywhere.
Concurrent activities are those activities that take place simultaneously.
The entities in the real world are often nested, and so are the objects in software systems. Each of
these nested objects may encapsulate nested activities again, and multiple interactions may
occur between these objects in parallel. For example, consider a bank with a number of clerks
serving customers. Provided it is open, customers may enter the bank and wait in line until they
can interact with one of the clerks at the counter. The clerks may in turn interact with other
employees or departments of the bank in order to fulfill the requests of the customers. All these
activities are happening at the same time and therefore are concurrent.

According to the object-oriented paradigm, each object is an autonomous agent, capable of
handling received requests. Active objects are objects that are capable of controlling and
scheduling the received requests before they are served by the object.
This observation leads to the following conclusions: to properly model real-world situations,
concurrent activities must be modeled. Each object must be capable of dealing with multiple,
concurrent requests. Requests may be serialized or trigger at the same time.
As stated before, our primary motivation for adopting concurrency lies with the modeling
issues that were just discussed. It should be remarked, however, that an object-oriented model
lends itself much more for a realisation on a distributed or parallel architecture, because objects
are concurrent by nature. It is thus relatively easy to identify tasks that can be executed in
parallel.

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