RECV Operations

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. 

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... 

To schedule operations in different processes so as to cause the SENDs and RECVs to execute in lockstep, the control step scheduler must consider not only the control steps in each process ( local scheduling), but the relationship between the control steps of all processes ( global scheduling). To achieve this lockstep execution, it may be necessary to insert delays into the control step schedule. This is shown in Figure 3-15, where a NO.OP (no operation) was inserted into the control step schedule of process Y to force the RECV to be executed at the same time as the corresponding SEND in process X. 

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. 

The final RECV / SEND pair of operators in process Vj are removed. 

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... 

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