Message Passing SEND Operations

In message passing, SEND and RECEIVE operations are used to synchronize, and to pass data via a specified communication channel. At one end of the message-passing spectrum, the SEND can refer to the specific process to which the information is sent, and the RECEIVE can refer to the specific process from which the information is received this option is referred to as direct naming. At the other end of the spectrum, the SEND and RECEIVE can refer to global mailboxes. Since the mailbox is not directly tied to a particular process, this method is more general, and provides better support for client / server interaction, where there are multiple clients or servers. 

In the Workbench, ISPS and VT SEND and RECV message-passing operations are used to communicate between processes. These operations were chosen because they serve the dual purpose of... 

The first of these system-level transformations, the Process Creation transformation, creates a process from the specified vtbody and its children. It marks the vtbody as a process, replaces each CALL to the vtbody with a SEND / RECV pair of message-passing operators, replaces each LEAVE from the vtbody with another SEND / RECV pair, and RESTARTS the vtbody so that it will execute continuously. The new process will execute concurrently with the other processes, and will be synthesized with a separate data path and controller. 

An example of Process Creation is shown in Figures 3-16 and 3-17. In this example, before the transformation, vtbody VI A CALLs vtbody V2 B, passing it values x and y. After the transformation, the CALL has been replaced with a SEND operator, and a corresponding RECV operator has been added to the beginning of vtbody V2 B values x and y are now passed via these message-passing operators. The LEAVE operator is replaced by a similar pair of SEND / RECV operators. After the transformation, vtbody V2 B is marked as a process, and is RESTARTed to execute continuously. 

The SEND and RECV message-passing operators that are used in multi-process designs as described in Chapter 3 are bound to special message modules. SEND modules are created with input ports to... 

Message passing via explicit blocking send and receive operations can be used for both synchronization and data-transfer. Information transfer takes place... 

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