Communicating sequential processes

The second type of node in HiFl expresses parallelism and is called a structure node. It is a network of nodes, of either type, in which ports of nodes are connected by edges. The nodes in such a network are concurrent processes that are only aware of their local state and communicate asynchronously with each other by edges. The communication between the AST nodes of such a network is according the model of communicating sequential processes (CSP) [15]. In the context of CSP, communication is seen as a shared event between two subprocesses. This means that the production of data in one AST process is synchronized with the consumption of data in another AST. 

C. A. R. Hoare. Communicating sequential processes. Prentice-Hall International, 1985. 

The software design of distributed systems necessarily involves the design of a set of communicating sequential processes, involving aspects of concurrency. The methods for the design of centralised multiprocessing systems have been developed over the last eighteen years (4-6). 

The programming language occam, which is derived from the theory of communicating sequential processes provides a good notation in which to pursue the design of distributed systems. Occam produces concise,... 

Hoare, C.A.R., Communicating Sequential Processes. Prentice-Hall 1985. 

Figure 2. Two models of decomposition. The one on the left is the standard subprocedure model where control is tranrferred to the subroutine and then returned when the subroutine completes. The one on the right is the more powerful model of communicating sequential processes. The main procedure spawn a co-routine with which it communicates when necessary while allowing parallel activity. The concurrent model is critical for interface specification. ...

Hoare, CA.R.(1983). Communicating sequential processes. Communications of the ACM26( ), 100-106. 

According to Snyder and Knoblauch (1971) to avoid a collision, pedestrians and drivers have to be aware of each other and to communicate with each other - at least partially. This interaction between the approaching driver and the crossing pedestrian requires both of them to perform at least six sequential processes (1) select the path of movement (2) visually scan the relevant scene for the potential or actual presence of the other (3) detect the other and assess his or her relative location (4) evaluate the intention of the other (5) decide on the proper course of action and (5) make the proper response to avoid a collision. If either the driver or the pedestrian performs all of these processes appropriately, a collision between them is avoided. However, if both fail to adequately perform any one of these processes then they are likely to collide. While it is a routine matter for drivers to visually search their environment for other traffic and potential obstacles (see Chapter 4), this is not the case for pedestrians. When pedestrians cross the street they must adjust their situation awareness. They have to change their direction of movement, attention, and visual search pattern whenever they change their walking path firom the curb to the road. Consequently, many crashes occur because drivers fail... 

Railway applications are characterized by a set of asynchronous sequential processes and communicate through variables specialized to achieve a common goal. A state machine models each sequential process. Applications (256 inputs/outputs maximum) create networks containing in the order of several hundred states and transitions. The places correspond to the variables of system states. The occurrence of an event reflects a change of system state and a transition. The variables are Boolean (with some exceptions). They are updated during every elementary system cycle (execution cycle 100 milliseconds). 

Besides combinatorial and parallel synthetic strategies [2, 3] in the past two decades the productive concepts of multicomponent processes, domino reactions and sequential transformations have considerably stimulated the synthetic scientific community [4-15]. In particular, combination of diversity and creation of functionality has merged into the field of diversity oriented syntheses [16-20] that have found broad application in the discovery and development of pharmaceutical lead structures, and quite recently and steadily increasing also in the conception of functional 7i-electron systems, such as chromophores, fluorophores, and electro-phores [21, 22]. 

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