Design and implementation of checkout station in t

Design and implementation of checkout station in large container inspection system (Part 2)

in order to overcome the above shortcomings, the second scheme is designed. Let's call it symmetric clien t? Server communication mode. As shown in Figure 2

in this mode, OM s and co s are equal, and they can make or accept requests to each other at the same time. In this way, the real-time performance of the system is improved. However, the workload of this scheme is more than twice that of the first scheme, and the program structure is complex. One process is added to OM s and co s respectively, two message channels are added, and one socket channel is added, which increases the overhead and burden of the system, and also affects the efficiency of style transmission. This method uses Hooke's law

the implementation of the third scheme is completed by integrating the advantages and disadvantages of the first two schemes. We call it the non blocking two-way single channel communication mode. Co s2om s communication has asynchronous characteristics, and tasks may overlap at the same time. The non blocking method in socket communication mechanism can realize two-way communication, and most of the previous places are almost blank; On the other hand, China's industry has developed rapidly in recent years. The two schemes realize one-way communication on one communication channel, so the final scheme is to realize the two-way communication of CO s2om s at the same time on a single channel (virtual dual channel) by using the non blocking socket communication mechanism on the basis of the first communication mode. As shown in Figure 1, the difference is that the communication parties here are no longer C? S relationship. This communication mode constitutes the basic mode of process communication between OMS and other distributed sites

3 cos interface technology discussion

co s graphical user interface design uses o SF? The development of Mo t if tool is divided into two parts: login interface and master interface. The login interface adopts the standard HP workstation login interface, including the main control area, diversity packing parking area, unpacking inspection area and command control area. In the process of interface design and development, using the support of X window system for 16b it font, BG code Chinese character library is loaded on HP workstation to realize the Sinicization of the whole interface. In addition, an important function of the checkout station is to submit the unpacking inspection conclusion to the OMS. The system also implements the Chinese character input module [2], and the inspector inputs the inspection conclusion and submits it to the OMS

the display of customs declaration and suspected mark images is realized through HP's Starbase graphics library. Since Mo t if only provides user interface design function, drawing operation still needs to call Xlib function to realize. The X Window environment is a network protocol environment. The application program gives the drawing command to X server through X protocol, and then X server drives the device driver to draw the drawing. Therefore, the response speed is very slow. When displaying a 64 level gray image, you can obviously feel the rolling effect of the image. HP's Starbase graphics library is developed for this situation. It makes use of the graphics hardware function of the machine, which greatly improves the display speed

for the printing of suspected mark images, the method of directly driving the printer under the UN IX operating system is adopted. In the UN IX operating system, the printer is managed as a character device file, so the print control code can be written directly into the device file to realize image printing [3]. We use traditional halftone technology to print pseudo gray and color images on HP laserj ET and epsonmj 21500k printers respectively

at the same time, the operation of the co s module is realized through the communication between the parent and child processes. The parent process is responsible for the general control of the graphical interface and co s, and the child process realizes the communication with OM s. The internal process communication of parent-child processes is realized through the message channel in UN ix2ipc[4] mechanism. Inter machine process communication is realized by socket[1] technology. The communication between CO s and OM s is realized on UN IX workstation, and the communication between them adopts the connection oriented communication mode [of which 300million cubic meters of wood need to be imported 5]

(author/Yao Dongsheng, Gao Wenhuan, Kang Kejun)

(Department of Engineering Physics, Tsinghua University, national professional laboratory of particle technology and radiation imaging,)