The send, receive, and reply operations may be synchronous or asynchronous. A synchronous operation blocks a process till the operation completes. An asynchronous operation is non-blocking and only initiates the operation. The caller could discover completion by some other mechanism discussed later. The notion of synchronous operations requires an understanding of what it means for an operation to complete. In the case of remote assignment, both the send and receive complete when the message has been delivered to the receiver. In the case of remote procedure call, the send, receive, and reply complete when the result has been delivered to the sender, assuming there is a return value. Otherwise, the send and receive complete when the procedure finishes execution. During the time the procedure is executing, the sender and receiver are in a rendezvous, as mentioned before. Note that synchronous/asynchronous implies blocking/not blocking but not vice versa, that is, not every blocking operation is synchronous and not every non blocking operation is asynchronous. For instance, a send that blocks till the receiver machine has received the message is blocking but not synchronous since the receiver process may not have received it. Similarly, we will see later a Xinu receive that is non-blocking but is not asynchronous. These definitions of synchronous/asynchronous operations are similar but not identical to the ones given in your text books, which tend to equate synchronous with blocking.
E-learning is to classroom learning as cell phones are to a pay phone at the bus station. At least it is in some ways. For instance, e-learning allows you to learn anywhere and usually at any time, as long as you have a properly configured computer. Cell phone allow you to communicate any time and usually anywhere, as long as you have a properly configured phone. E-learning can be CD-ROM based, Network-based, Intranet-based or Internet-based. It can include text, video, audio, animation and virtual environments. It can be a very rich learning experience that can even surpass the level of training you might experience in a crowded classroom. It's self-paced, hands-on learning. The quality of the electronic-based training, as in every form of training, is in its content and its delivery. E-learning can suffer from many of the same pitfalls as classroom training, such as boring slides, monotonous speech, and little opportunity for interaction. The beauty of e-learning, however, is that new software allows the creation of very effective learning environments that can engulf you in the material. We'll use software from Trainer soft as an example to show you how the process works.