C Programming

enum, void and const are relatively new keywords in C

new, on the other hand, isn't a keyword in C

On each system clock tick, at interval set by design...

• If no other runnable threads, return from clock interrupt.
• Save the currently running thread's context.
• Restore the next runnable thread's context.
• Return from clock tick interrupt.

Note: Most modern schedulers combine round-robin with priority. In the priority scheme, any runnable thread with a higher priority than the interrupted thread takes precedence. If there are none, then round-robin applies at the current priority. If there are no runnable threads at the current priority, lower priorities are considered until we reach the idle priority thread, which, by the way, is always runnable.

Also, there is usually an algorithm that adjusts thread priority dynamically. As the thread runs, if it stays runnable its priority slowly drops from its initial base priority. If it is constantly blocking and then then becoming runnable, its priority increases, often faster than it decreases. This makes interactive threads appear to be very responsive, while CPU intensive threads slowly defer to interactive threads. This is usually a good compromise between responsiveness and throughput.

Disadvantages And Constraints

Some disadvantages and constraints of e-commerce include the following.

Time for delivery of physical products .

It is possible to visit a local music store and walk out with a compact disc, or a bookstore and leave with a book. E-commerce is often used to buy goods that are not available locally from businesses all over the world, meaning that physical goods need to be delivered, which takes time and costs money. In some cases there are ways around this, for example, with electronic files of the music or books being accessed across the Internet, but then these are not physical goods.

Physical product, supplier & delivery uncertainty

When you walk out of a shop with an item, it's yours. You have it; you know what it is, where it is and how it looks. In some respects e-commerce purchases are made on trust. This is because, firstly, not having had physical access to the product, a purchase is made on an expectation of what that product is and its condition. Secondly, because supplying businesses can be conducted across the world, it can be uncertain whether or not they are legitimate businesses and are not just going to take your money. It's pretty hard to knock on their door to complain or seek legal recourse! Thirdly, even if the item is sent, it is easy to start wondering whether or not it will ever arrive.

Perishable goods

Forget about ordering a single gelato ice cream from a shop in Rome! Though specialised or refrigerated transport can be used, goods bought and sold via the Internet tend to be durable and non-perishable: they need to survive the trip from the supplier to the purchasing business or consumer. This shifts the bias for perishable and/or non-durable goods back towards traditional supply chain arrangements, or towards relatively more local e-commerce-based purchases, sales and distribution. In contrast, durable goods can be traded from almost anyone to almost anyone else, sparking competition for lower prices. In some cases this leads to disintermediation in which intermediary people and businesses are bypassed by consumers and by other businesses that are seeking to purchase more directly from manufacturers.

Limited and selected sensory information.

The Internet is an effective conduit for visual and auditory information: seeing pictures, hearing sounds and reading text. However it does not allow full scope for our senses: we can see pictures of the flowers, but not smell their fragrance; we can see pictures of a hammer, but not feel its weight or balance. Further, when we pick up and inspect something, we choose what we look at and how we look at it. This is not the case on the Internet. If we were looking at buying a car on the Internet, we would see the pictures the seller had chosen for us to see but not the things we might look for if we were able to see it in person. And, taking into account our other senses, we can't test the car to hear the sound of the engine as it changes gears or sense the smell and feel of the leather seats. There are many ways in which the Internet does not convey the richness of experiences of the world. This lack of sensory information means that people are often much more comfortable buying via the Internet generic goods - things that they have seen or experienced before and about which there is little ambiguity, rather than unique or complex things.

Returning goods

Returning goods online can be an area of difficulty. The uncertainties surrounding the initial payment and delivery of goods can be exacerbated in this process. Will the goods get back to their source? Who pays for the return postage? Will the refund be paid? Will I be left with nothing? How long will it take? Contrast this with the offline experience of returning goods to a shop.

Privacy, security, payment, identity, contract.

Many issues arise - privacy of information, security of that information and payment details, whether or not payment details (eg credit card details) will be misused, identity theft, contract, and, whether we have one or not, what laws and legal jurisdiction apply.

Defined services & the unexpected .

E-commerce is an effective means for managing the transaction of known and established services, that is, things that are everyday. It is not suitable for dealing with the new or unexpected. For example, a transport company used to dealing with simple packages being asked if it can transport a hippopotamus, or a customer asking for a book order to be wrapped in blue and white polka dot paper with a bow. Such requests need human intervention to investigate and resolve.

Personal service .

Although some human interaction can be facilitated via the web, e-commerce can not provide the richness of interaction provided by personal service. For most businesses, e-commerce methods provide the equivalent of an information-rich counter attendant rather than a salesperson. This also means that feedback about how people react to product and service offerings also tends to be more granular or perhaps lost using e-commerce approaches. If your only feedback is that people are (or are not) buying your products or services online, this is inadequate for evaluating how to change or improve your e-commerce strategies and/or product and service offerings. Successful business use of e-commerce typically involves strategies for gaining and applying customer feedback. This helps businesses to understand, anticipate and meet changing online customer needs and preferences, which is critical because of the comparatively rapid rate of ongoing Internet-based change.

Size and number of transactions.

E-commerce is most often conducted using credit card facilities for payments, and as a result very small and very large transactions tend not to be conducted online. The size of transactions is also impacted by the economics of transporting physical goods. For example, any benefits or conveniences of buying a box of pens online from a US-based business tend to be eclipsed by the cost of having to pay for them to be delivered to you in Australia. The delivery costs also mean that buying individual items from a range of different overseas businesses is significantly more expensive than buying all of the goods from one overseas business because the goods can be packaged and shipped together.