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The ACEServiceConfig Class
ru-brd

5.4 the ace_service_config class 【程序编程相关:使用VB求解华容道问题】

【推荐阅读:提高视觉系统颜色识别鲁棒性的一种方案】

before a service can execute, it must be configured into an application´s address space. one way to configure services into a networked application is to statically link the functionality provided by its various classes and functions into separate os processes, and then manually instantiate or initialize them at run time. we used this approach in the logging server examples in chapters 3 and 4 and throughout c++npv1, where the logging server program runs in a process that handles log records from client applications. although our use of the ace reactor framework in earlier chapters improved the networked logging server´s modularity and portability, the following drawbacks arose from statically configuring the reactor_logging_server class with its main() program: 【扩展信息:利用VB解决华容道问题的源代码】

motivation

在服务可以执行前,它必须配置进应用程序.一种方法是静态的连接由不同的类与函数提供的功能到独立的os进程中,然后在运行时手工实例化他们.我们在c++npv1的第3,第4章中使用这种方法,logging server运行在一个处理客户日志的进程中.虽然我们使用了ace reactor框架提高了模块化,可移植性,但是在main()中静态配置reactor_logging_server出现了类下面的问题:

service configuration decisions are made prematurely in the development cycle, which is undesirable if developers don´t know the best way to collocate or distribute services in advance. moreover, the "best" configuration may change as the computing context changes. for example, an application may write log records to a local file when it´s running on a disconnected laptop computer. when the laptop is connected to a lan, however, it may forward log records to a centralized logging server. forcing networked applications to commit prematurely to a particular service configuration impedes their flexibility and can reduce their performance and functionality. it can also force costly redesign and reimplementation later in a project´s life cycle.

开发周期中过早的做出服务配置的决定,开发人员不知道最佳的配置或分配服务.而且最佳的配置会随着计算机环境的变化而变化.应用程序可以将长纪录写到一个本地文件当网络断开时,也可以将记录转发给日志服务器当网络连接上时.过早的提交配置阻碍了灵活性减少了功能与效率.加强了重新实现的昂贵开销.

modifying a service may affect other services adversely if the implementation of a service is coupled tightly with its initial configuration. to enhance reuse, for example, a logging server may initially reside in the same program as other services, such as a name service. if the other services change, however, for example if the name service lookup algorithm changes, all existing code in the server would require modification, recompilation, and static relinking. moreover, terminating a running process to change some of its service code would also terminate the collocated logging service. this disruption in service may not be acceptable for highly available systems, such as telecommunication switches or customer care call centers [ss94].

如果一个服务与他初始配置有紧密联系,修改一个服务可能影响其他服务adversely.为了增强重用,举例,一个logging server可能与其他服务,如名字服务,驻留在同一个程序中.如果其他服务变化了,如名字服务修改了查找算法,服务中所有的代码需要重新修改,编辑,静态连接.而且终止一个运行的进程来改变服务中的代码也结束了日志服务.这个中断在一些高可靠系统中是不可接受的,如telecommunication switches与customer care call centers.

system performance may scale poorly since associating a separate process with each service ties up os resources, such as i/o handles, virtual memory, and process table slots. this design is particularly wasteful if services are often idle. moreover, processes can be inefficient for many short-lived communication tasks, such as asking a time service for the current time or resolving a host address request via the domain name service (dns).

系统性能的扩展小因为相互关联的进程与它的每一个服务与系统资源紧密联系,如i/o handle,虚拟内存,与进程槽.这种设计是非常浪费的如果服务经常处理空闲.而且进程可能低效率的服务许多short-lived communication tasks,例如询问time service获得当前时间,或者解析一个主机地址通过dns.

to address the drawbacks of purely static configurations, the ace service configurator framework defines the ace_service_config class.

class capabilities

ace_service_config implements the facade pattern [gof] to integrate other classes in the ace service configurator framework and coordinate the activities necessary to manage the services in an application. this class provides the following capabilities:

ace_service_config 实现了facade pattern [gof] 与其他ace service configurator framework中的类结合在一起,调整必需的行为来管理程序中其他的服务.这个类提供了以下的能力: it interprets a scripting language that allows applications or administrators to provide the ace service configurator framework with commands, called directives, to locate and initialize a service´s implementation at run time, as well as to suspend, resume, reinitialize, and/or shut down a component after it´s been initialized. directives can be specified to ace_service_config in either of two ways:

他解释了脚本语言允许程序或者管理员在运行时提供ace service configurator framework命令,调用指令,来定位与初始化服务的实现,例如挂起,恢复,重新初始化,shut down一个部件在他初始化后.指令可以用两种方法指定:

using configuration files (named svc.conf by default) that contain one or more directives

使用包含一条或者多条指定的配置文件,默认是svc.conf

programmatically, by passing individual directives as strings

programmatically,通过字符串方式传递单独指令

it supports the management of services located in the application (the so-called static services), as well as those that must be linked dynamically (the so-called dynamic services) from separate shared libraries (dlls).

他支持服务管理.

it allows service reconfiguration at run time using the following mechanisms:

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