CHAPTER 1 The big picture Generate content (say
CHAPTER 1 The big picture Generate content (say read a static file) A request arrives Send results to the user Call method in module Is the requested file handled by a module? Yes No Figure 1.3 Executing a module with a web server API servlets or JSPs they re based on), the industry addressed the performance shortcomings of CGI by introducing a new web extension mechanism, the web server API. 1.3.2 Web server APIs In a web server API, the application developer first writes a loadable module (a DLL in Microsoft Windows, a shared object in UNIX) that follows the API definition for the specific server. The web server loads this module on startup, and calls it whenever a user makes a request which should be handled by that module. Popular APIs include Netscape Server Application Programming Interface (NSAPI) for Netscape Enterprise Server, and Internet Information Server Application Programming Interface (ISAPI), though all popular servers have one. Most web servers use a configuration file which contains directives specifying which modules to load and the requests a particular module should handle. By loading the extension module directly into the web server, we gain unmatched performance since invoking our extension is merely a function call. Unlike CGI, the function calls take place within a single process that is already running; namely, the web server process itself. We can also save state inside the web server address space. This allows us to save the results of expensive processing (such as objects that are slow to initialize) in a central location so that they can be shared by requests instead of being created over and over again. These two features alone address both of the major shortcomings we saw with CGI. Server API drawbacks Oddly enough, the unmatched performance available by writing to the web server API did not win this extension method the popularity of CGI or other extension techniques that we will discuss. It failed to catch on for several reasons: Each server has a different API. This means there is no standard that can be learned once and applied across servers.
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