Research And Realization Of Station Computer

In a hierarchical organization, Station Computer System (SC System), as the intermediation between station terminal device and line centre computer system, installed in each station on site, collecting the raw operating data, transmitting the ticket information, is one of the important parts of Automatic Fare Collection System.SC System adopts multi-process and multi-thread architecture, which multi-process makes the hierarchy of system simple and the logic clear. It is easy to implementation of parallel processing and to system upgrade; multi-thread makes up the deficiency of too many processes. It enhances the capacity of parallel processing. SC System comprises of five parallel processes: management process, user interface process, upper layer communication process, lower layer communication process and data processing process. These five processes create threads when necessary to complete user task.The multi-process and multi-thread system operation is based on the cooperation among multiple processes and threads. This paper offers the solution to inter-process communication, process synchronization, mutual exclusion and deadlock of SC System.Main results:(1) Comparing with common methods of inter-process communication, we finally choose named pipes. In this paper, we explain in detail how to create, connect, communicate and close named pipes. We also present the overlapped I/O mechanism for the realization of communication among named pipes server and clients.(2) We manage the use of critical resource by the adoption of file mapping. The resource requisition matrix is set for SC System at first. Resource assignments act as file mapping. When process/thread executes task, it obtains the information of resource requisition from the matrix. It then accesses to the mapping file for checking current resource assignments in order to determine whether it continues to execute current operation. Since only one process could do write operation to mapping file at one time, the paper offers the technique, called mutually exclusive kernel, to ensure mutually exclusive access to the mapping file among multiple processes to realize process synchronization.(3) By the method of preventing part of the four requirements for resulting deadlock, we exclude the possibility of system deadlock.