Abstract:
Method and apparatus for processing java server pages (JSPs) which reduces the delays resulting from a first time invocation of a JSP. One embodiment provides a method for processing JSPs for a java virtual machine (JVM), comprising: selecting one or more JSP files to be processed for the JVM; translating the JSP files to java source code files; inserting quick exit codes to java source code files; compiling java source code files to servlet class files; and loading servlet class files into the JVM.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to an improved data processing system. More particularly, the present invention relates to a method and apparatus for processing JSP® pages for an application server. 
   2. Description of the Related Art 
   The Internet has become a cultural fixture as a source of both information and entertainment. Many businesses are creating Internet sites as an integral part of their marketing efforts, informing consumers of the products or services offered by the business or providing other information seeking to engender brand loyalty. Many federal, state, and local government agencies are also employing Internet sites for informational purposes, particularly agencies which must interact with virtually all segments of society such as the Internal Revenue Service and secretaries of state. Providing informational guides and/or searchable databases of online public records may reduce operating costs. Further, the Internet is becoming increasingly popular as a medium for commercial transactions. 
   The term “Internet” generally refers to the collection of networks and gateways that use the TCP/IP suite of protocols. Currently, the most commonly employed method of transferring data over the Internet is to employ the World Wide Web environment, also called simply “the Web”. Other Internet resources exist for transferring information, such as File Transfer Protocol (FTP), but have not achieved the popularity of the Web. In the Web environment, servers and clients effect data transaction using the Hypertext Transfer Protocol (HTTP), a known protocol for handling the transfer of various data files (e.g., text, still graphic images, audio, motion video, etc.). The information in various data files is formatted for presentation to a user by a standard page description language, the Hypertext Markup Language (HTML). In addition to basic presentation formatting, HTML allows developers to specify “links” to other Web resources identified by a Uniform Resource Locator (URL). A URL is a special syntax identifier defining a communications path to specific information. Each logical block of information accessible to a client, called a “page” or a “Web page”, is identified by a URL. The URL provides a universal, consistent method for finding and accessing this information, not necessarily for the user, but mostly for the user&#39;s Web “browser”. A browser is a program capable of submitting a request for information identified by a URL at the client machine. Retrieval of information on the Web is generally accomplished with an HTML-compatible browser. 
   Web content is often dynamic because of various changes made by developers and other users publishing or making available web content, such as Web pages. Even static pages are occasionally updated. Web servers provide static content and dynamic content to various users. Static content contain data from files stored at a server. Dynamic content is constructed by programs executing at the time a request is made. Dynamic content is often present at a web site in an effort to provide customized pages and updated information to various users that may visit the site. Dynamic content may be provided utilizing JavaServer Pages® (JSP® pages), based on Java® platform technology. Compared to other methods of delivering dynamic content, JSP® pages provide advantages such as separation of dynamic and static contents (i.e., separation of application logic and web page design), which reduces the complexity of web site development and makes the site easier to maintain. 
   The first invocation of a JSP® page requires several preliminary steps which are performed once for the application server running the JSP® page. First, a temporary servlet source code (JAVA® source code) is created based on the contents of the JSP® page (i.e., filename.jsp file is translated to filename.java file). Second, the servlet source code is compiled into a servlet class file (i.e., filename.java file is translated to filename.class file). These two steps are performed only once until the JSP® page has been changed (i.e., the file containing the page is modified). Third, a bytecode verification is processed against the servlet class file. Fourth, a direct executable is generated for the servlet class file. Lastly, the direct executable is loaded into the Java® virtual machine on the application server. The last three steps are performed once per Java® virtual machine. 
   Although subsequent invocations of the same JSP® pages are generally fast because these preliminary steps are performed only one time, the first invocation of a JSP® pages may require substantial processing time, resulting in a noticeable delay to the end user. The delay problem is compounded when JSP® pages are written to invoke other JSP® pages, causing the total delay to be the serial sum of the processing time for each JSP® page. 
   Therefore, there is a need for a method and apparatus for processing JSP® pages for an application server which reduces the delays resulting from a first time invocation of a JSP® page. 
   SUMMARY OF THE INVENTION 
   The present invention generally provides methods and apparatus for processing JSP® pages for an application server which reduces the delays resulting from a first time invocation of a JSP® pages. One embodiment of the present invention provides a pre-touch mechanism that traverses through JSP® page and loads them into a Java® virtual machine for a given application (e.g., a Web Application such as IBM&#39;s WebSphere®). The pre-touch mechanism performs the preliminary steps required for execution of the JSP® pages prior to a first invocation of the JSP® pages by an end user. Thus, the pre-touch mechanism substantially reduces the processing time required for the first invocation of a JSP® page, and the end-user does not experience the typical delays presented by a first invocation of a JSP® page. 
   In one embodiment, the pre-touch mechanism adds one or more initialization parameters for a JSP® page processor which determine how the JSP® pages are to be processed for a JVM®. The initialization parameters include: prepareJSPs parameter, prepareJSPThreadCount parameter, and prepareJSPAttribute parameter. The prepareJSPs parameter allows an administrator to select which JSP® pages are processed through the pre-touch mechanism. The prepareJSPThreadCount parameter specifies a numeric value which indicates the number of threads to be spawned by the JSP® page processor for the pre-touch mechanism. The prepareJSPAttribute parameter allows a quick exit immediately after the class has been loaded into the JSP® page, and thus, avoids any overhead/inefficiency resulting from execution of the JSP® page&#39;s service method. 
   One embodiment provides a method for processing Java server pages (JSP® pages) for a Java® virtual machine, comprising: selecting one or more JSP® page files to be processed for the Java® virtual machine; translating the JSP® page files to Java® source code files; inserting quick exit codes to Java® source code files; compiling Java® source code files to servlet class files; and loading servlet class files into the Java® virtual machine. 
   Another embodiment provides a system for processing JSP® pages, comprising: an application server computer comprising one or more processors and a memory, the memory containing a JSP® page processor and a Java® virtual machine, wherein the JSP® page processor is configured to selectively load one or more JSP® page class files into the Java® virtual machine prior to user requests for JSP® page files. 
   Yet another embodiment provides a method for processing a JSP® page for a Java® virtual machine prior to a user request for the JSP® page, comprising: loading the JSP® page into the Java® virtual machine; invoking the JSP® page; and terminating execution of the JSP® page prior to execution of user codes in the JSP® page. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       FIG. 1  depicts a pictorial representation of a distributed data processing system (also referred herein as a network environment)  100  in which the present invention may be implemented. 
       FIG. 2  is a block diagram illustrating one embodiment of a data processing system that may be implemented as a client computer. 
       FIG. 3  is a block diagram illustrating one embodiment of a data processing system that may be implemented as a server system. 
       FIG. 4  is a block diagram illustrating an execution environment  400  for a Web application server  410 . 
       FIG. 5  is a flow diagram illustrating one embodiment of a method of processing JSP® pages utilizing a pre-touch mechanism. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention generally provides methods and apparatus for processing JSP® pages for an application server which reduces the delays resulting from a first time invocation of a JSP® page. One embodiment of the present invention provides a pre-touch mechanism that traverses through JSP® pages and loads them into a Java® virtual machine for a given application. The pre-touch mechanism performs the preliminary steps required for execution of the JSP® pages prior to a first invocation of the JSP® pages by an end user. Thus, the pro-touch mechanism substantially reduces the processing time required for the first invocation of a JSP® page, and the end-user does not experience the typical delays presented by a first invocation of a JSP® page. In one embodiment, the pre-touch mechanism adds one or more initialization parameters for the JSP® page processor which determine how the JSP® pages are to be processed for a Java® virtual machine. 
   Embodiments of the invention may be implemented as a program product for use with a computer system such as, for example, the network environment  100  shown in  FIG. 1  and described below. The program(s) of the program product defines functions of the embodiments (including the methods described herein) and can be contained on a variety of signal-bearing media. Illustrative signal-bearing media include, but are not limited to: (i) information permanently stored on non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive); (ii) alterable information stored on writable storage media (e.g., floppy disks within a diskette drive or hard-disk drive); and (iii) information conveyed to a computer by a communications medium, such as through a computer or telephone network, including wireless communications. The latter embodiment specifically includes information downloaded from the Internet and other networks. Such signal-bearing media, when carrying computer-readable instructions that direct the functions of the present invention, represent embodiments of the present invention. 
   In general, the routines executed to implement the embodiments of the invention, may be part of an operating system or a specific application, component, program, module, object, or sequence of instructions. The computer program of the present invention typically is comprised of a multitude of instructions that will be translated by the native computer into a machine-readable format and hence executable instructions. Also, programs are comprised of variables and data structures that either reside locally to the program or are found in memory or on storage devices. In addition, various programs described hereinafter may be identified based upon the application for which they are implemented in a specific embodiment of the invention. However, it should be appreciated that any particular program nomenclature that follows is used merely for convenience, and thus the invention should not be limited to use solely in any specific application identified and/or implied by such nomenclature. 
   With reference now to the figures,  FIG. 1  depicts a pictorial representation of a distributed data processing system (also referred herein as a network environment)  100  in which the present invention may be implemented. The distributed data processing system  100  contains a network  102 , which is the medium used to provide communications links between various devices and computers connected together within distributed data processing system  100 . Network  102  may include permanent connections, such as wire or fiber optic cables, or temporary connections made through telephone connections. Further, network  102  may include wireless connections. 
   In the depicted example, a server computer  104  is connected to network  102  along with storage unit  106 . In addition, client computers  108 ,  110 , and  112  also are connected to a network  102 . These clients  108 ,  110 , and  112  may be, for example, personal computers or network computers. For purposes of this application, a network computer is any computer, coupled to a network, which receives a program or other application from another computer coupled to the network. In the depicted example, the server  104  may provide data, such as boot files, operating system images, and applications to the clients  108 – 112 , which are clients to server  104 . The distributed date processing system  100  may include other forms of server systems (not shown), which also may provide data to clients  108 – 112 . For example, one form of a server system may comprise two or more servers that have been logically associated with each other or interconnected as a cluster. The distributed data processing system  100  may include additional servers, clients, and other devices not shown. 
   In the depicted example, the network  102  is the Internet. The distributed data processing system  100  also may be implemented as a number of different types of networks, such as, for example, an intranet, a local area network (LAN), or a wide area network (WAN).  FIG. 1  is intended as an example, and not as an architectural limitation for the present invention. 
     FIG. 2  is a block diagram illustrating one embodiment of a data processing system that may be implemented as a client computer, such as client  108 – 112  in  FIG. 1 . The client computer  222  includes a Central Processing Unit (CPU)  228  connected via a bus  230  to a memory  232 , storage  234 , input device  236 , output device  238  and a network interface device  237 . The input device  236  can be any device to give input to the client computer  222 . For example, a keyboard, keypad, light-pen, touch-screen, track-ball, or speech recognition unit, audio/video player, and the like could be used. The output device  238  is preferably any conventional display screen and, although shown separately from the input device  236 , the output device  238  and input device  236  could be combined. For example, a display screen with an integrated touch-screen, and a display with an integrated keyboard, or a speech recognition unit combined with a text speech converter could be used. 
   The network interface component  237  may be any entry/exit component configured to allow network communications between the client computer  222  and the server computers  224  via the network  226 . For example, the network interface component  237  may be a network adapter or other network interface card (NIC). 
   Memory  232  is preferably random access memory sufficiently large to hold the necessary programming and data structures of the invention. While memory  232  is shown as a single entity, it should be understood that memory  232  may in fact comprise a plurality of modules, and that memory  232  may exist at multiple levels, from high speed registers and caches to lower speed but larger DRAM chips. Memory  232  contains a browser program  240  that, when executed on CPU  228 , provides support for navigating between the various servers  104  and locating network addresses at one or more of the servers  104 . In one embodiment, the browser program  240  includes a web-based Graphical User Interface (GUI), which allows the user to display web pages located on the Internet. 
   The client computer  222  is generally under the control of an operating system  258 , which is also located in memory  232 . Illustrative operating systems which may be used to advantage include IBM&#39;s AIX operating system, Linux and Windows. More generally, any operating system supporting browser functions may be used. 
   Storage  234  is preferably a Direct Access Storage Device (DASD), although it is shown as a single unit, it could be a combination of fixed and/or removable storage devices, such as fixed disc drives, floppy disc drives, tape drives, removable memory cards, or optical storage. Memory  232  and storage  234  could be part of one virtual address space spanning multiple primary and secondary storage devices. 
   Referring to  FIG. 3 , a block diagram depicts one embodiment of a data processing system that may be implemented as a server system, such as server  104  in  FIG. 1 . Data processing system  300  may be a symmetric multiprocessor (SMP) system including a plurality of processors  302  and  304  connected to system bus  306 . Alternatively, a single processor system may be employed. Also connected to system bus  306  is memory controller/cache  308 , which provides an interface to local memory  309 . I/O bus bridge  310  is connected to system bus  306  and provides an interface to I/O bus  312 . Memory controller/cache  308  and I/O bus bridge  310  may be integrated as depicted. 
   Memory  309  is a random access memory sufficiently large to hold the necessary programming and data structures that are located on the server computer  300 . The programming and data structures may be accessed and executed by the processors  302 ,  304  as needed during operation. As shown, the memory  309  includes a Hypertext Transfer Protocol (HTTP) server process  345  adapted to service requests from the client computers. For example, process  345  may respond to requests to access electronic documents  346  (e.g., HTML documents) residing in server memory  309  or storage  332 . The http server process  345  is merely illustrative and other embodiments adapted to support any known and unknown protocols are contemplated, The memory  309  also includes an application server  350 , such as IBM&#39;s WebSphere® Application Server. The application server  350  provides a JAVA® enabled environment for processing servlets and JSP® pages and handles browser requests for servlets and JSP® pages. 
   Peripheral component interconnect (PCI) bus bridge  314  connected to I/O bus  312  provides an interface to PCI local bus  316 . A number of modems may be connected to PCI bus  316 . Typical PCI bus implementations will support a plurality of PCI expansion slots or add-in connectors. Communications links to network computers  108 – 112  in  FIG. 1  may be provided through modem  318  and/or network adapter  320  connected to PCI local bus  316  through add-in boards. 
   Additional PCI bus bridges  322  and  324  provide interfaces for additional PCI buses  326  and  328 , from which additional modems or network adapters may be supported. In this manner, server  300  allows connections to multiple network computers. A memory-mapped graphics adapter  330  and hard disk  332  may also be connected to I/O bus  312  as depicted, either directly or indirectly. 
   Those of ordinary skill in the art will appreciate that the hardware depicted in  FIG. 3  may vary. For example, other peripheral devices, such as optical disk drives and the like, also may be used in addition to or in place of the hardware depicted. The depicted example is not meant to imply architectural limitations with respect to the present invention. The data processing system depicted in  FIG. 3  may be, for example, an IBM RISC/System 6000 system, a product of International Business Machines Corporation in Armonk, N.Y., running the Advanced Interactive Executive (AIX) operating system. 
     FIG. 4  is a block diagram illustrating an execution environment  400  for a Web application server  410 . As shown in  FIG. 4 , the execution environment  400  includes a server system  405  containing a Web application server  410  and an HTTP server  415  (i.e., one embodiment of server system  300 , application server  350  and HTTP server  345 ). A client system  420  having a browser  425  (i.e., one embodiment of client system  222  and browser  240 ) is also disposed in communication with the server system  405 . Storage devices  430  (i.e., one embodiment of storage  106 ) containing one or more relational databases  435  may also disposed in communication with the server system  405 . These relational databases may include a DB2 database  440 , a database  445  containing classes and HTML/JSP® page files. The Web application server  410  includes a servlet engine  450  for processing a Web application  475  containing servlets  455  and a JSP® page processor  460 . The servlet engine  450  is program that runs within the application server  410  and handles the requests for servlets, JSP® pages and other server-side coding. The servlet engine  450  creates instances of servlets, initiates servlets, acts as a request dispatcher, and maintains servlet context for use by the server applications. The JSP® page processor  460  processes loaded JSP® pages  465  which have been translated and loaded into a Java® virtual machine  470  for execution. The JSP® page processor  460  also processes JSP® pages for their first time loading into a Java® virtual machine. Additionally, the JSP® page processor  460  may also receive requests from a client to a JSP® page and generate responses from the JSP® page to the client. 
   The Java® virtual machine is a virtual computer component that resides only in memory. The term “Java® virtual machine” is a Java specific term for “address space.” Accordingly, in one embodiment, Java® virtual machine is used herein interchangeably with “address space.” The Java® virtual machine allows Java programs to be executed on different platforms as opposed to only the one platform for which the code was compiled. In this manner, Java® is able to support applications for many types of data processing systems, which may contain a variety of central processing units and operating systems architectures. To enable a Java® application to execute on different types of data processing systems, a compiler typically generates an architecture-neutral file format—the compiled code is executable on many processors, given the presence of the Java® run time system. The Java® compiler generates bytecode instructions that are non-specific to particular computer architectures. A bytecode is a machine independent code generated by the Java® compiler and executed by a Java® interpreter. A development environment, such as the Java Development Kit® (JDK®) available from Sun Microsystems, Inc., may be used to build Java® byte code from Java® language source code and libraries. 
   One embodiment of the present invention provides a pre-touch mechanism that traverses through JSP® pages and loads them into a Java® virtual machine for a given application (e.g., a Web Application such as IBM&#39;s WebSphere®). The pre-touch mechanism performs the preliminary steps required for execution of the JSP® pages prior to a first invocation of the JSP® pages by an end user. Thus, the pre-touch mechanism substantially reduces the processing time required for the first invocation of a JSP® page, and the end-user does not experience the typical delays presented by a first invocation of a JSP® page. In one embodiment, the pre-touch mechanism adds one or more initialization parameters for the JSP® page processor. The initialization parameters include: prepareJSPs parameter, prepareJSPThreadCount parameter, and prepareJSPAttribute parameter. 
   The prepareJSPs parameter specifies a kilobyte threshold value. This parameter is first utilized to determine whether to proceed with the pre-touch mechanism for all the JSP® pages to be processed for the particular Web application. When This parameter is specified, all JSP® pages to be processed for the particular Web application are translated from the filename.jsp file to the filename.java file and then compiled to the filename.class file. For each of these JSP ® pages whose kilobyte size exceeds the kilobyte threshold value, the JSP® page is processed for bytecode verification, generation of a direct executable, and loading of the direct executable into the Java® virtual machine. Since the amount of JSP® page processing time is generally proportional to the size of the JSP® page source file, the prepareJSPs parameter allows an administrator to select which JSP® page are processed through the pre-touch mechanism. If the prepareJSPs parameter is specified as zero kilobytes, each JSP® page is processed through the pre-touch mechanism. 
   The prepareJSPThreadCount parameter specifies a numeric value which indicates the number of threads to be spawned by the JSP® page processor for the pre-touch mechanism. Multiple threads enable parallel processing of JSP® pages and utilize more efficiently the available CPUs on the server system. 
   The prepareJSPAttribute parameter specifies an alphanumeric string value. The existence of this parameter is checked at the starting execution of the JSP® page. If the parameter is specified, the JSP® page performs a quick exit before attempting to execute any user code within the JSP® page. The prepareJSPAttribute parameter provides an important function for the pre-touch mechanism in eliminating inefficiencies and errors/exceptions caused by JSP® pages being called or executed out of context. Typically, to load a JSP® page class file into a Java® virtual machine requires invocation of The JSP® page&#39;s service method. However, even just invoking a JSP® page to achieve classloading into the Java® virtual machine can be a problem because the JSP® page is being called out of context. Since JSP® pages, often require Java® classes to be passed in when called, being called out of context can cause exceptions to be generated, resulting in inefficiency. Even if no errors are logged, there is no point to allowing the JSP® page&#39;s entire service method to run to completion. The prepareJSPAttribute parameter allows a quick exit immediately after the class has been loaded into the Java® virtual machine, and thus, avoids any overhead/inefficiency resulting from execution of the JSP® page&#39;s service method. 
   As exemplified by  FIG. 4 , one embodiment of the pre-touch mechanism is implemented utilizing a JSP® page processing servlet (or JSP® page processor  460 ) residing on the application server  410 . For example, the JSP® page processing servlet (e.g., in IBM&#39;s WebSphere) will check these attributes (i,e., initialization parameters) and perform the required tasks for processing the JSP® pages. 
     FIG. 5  is a flow diagram illustrating one embodiment of a method of processing java server pages utilizing the pre-touch mechanism. The method  500  starts at block  502  and proceeds to initialize the web application at block  504 . Although this illustrated embodiment is described along with an initialization of a Web application, it is contemplated that the method may be performed separately from an initialization of a Web application. In one embodiment, the servlet engine  450  processes the initialization of the web application  475 . The method  500  then proceeds to retrieve configuration data at block  506  to determine whether the JSP® page processor  460  is configured for performing the Pre-touch mechanism (block  508 ). In one embodiment, the method  500  check for the presence of the prepareJSPs initialization parameter in the JSP® page processor  460 . If the prepareJSPs parameter is not specified or does not exist, the pre-touch mechanism is not launched and the method  500  ends at block  590 . 
   If the presence of The prepareJSPs parameter is validated, a pre-touch thread is spawned (block  510 ) from the servlet engine&#39;s initialization of the Web application. Once the pre-touch thread has been spawned, the servlet engine  450  may proceed or resume with other tasks while the pre-touch thread continues. The configuration parameters for the pre-touch mechanism are evaluated at block  512 , and the JSP® pages to be processed for the Web Application are collected at block  514 . Next, at block  516 , a plurality of worker threads are spawned to process the JSP® pages. The number of threads spawned is specified by the prepareJSPThreadCount parameter. All Threads process the JSP® pages contemporaneously, and each thread may process a plurality of JSP® pages sequentially and continuously. 
   For each thread spawned, the following steps are performed for each JSP® page processed. The JSP® page processor  460  is called at block  518 , and the .jsp file is translated into a .java file (i.e., java source code) at block  520 . At block  522 , a quick exit code is inserted into the .java file utilizing the prepareJSPAttribute parameter. The quick exit code generally represents java source code which, after the class file has been loaded into the Java® virtual machine and at the beginning of the execution of the JSP® page, causes the JSP® page to check for the existence of the prepareJSPAttribute parameter. The .java file is then compiled into a .class file (i.e., servlet class file) at block  524 . At block  526 , the JSP® page processor  460  performs a classload function for the JSP® page whose size exceeds the kilobyte threshold value defined by the prepareJSPs parameter. In one embodiment, a bytecode verification is processed against the .class file. Then, the .class file is loaded into the Java® virtual machine  470 . After class loading, the servlet class file is invoked based on the prepareJSPs initialization parameter at block  527 . Thus, only the JSP® pages whose size exceed the kilobyte threshold value are invoked after classloading. 
   At block  528 , the .class file undergoes JIT (just in time) optimization, producing a direct executable (unless the Java® virtual machine is not configured to process the JSP® page in interpret mode, in which case the Java® virtual machine will execute the .class file bytecodes directly). At block  530 , the JSP® page&#39;s direct executable code is executed with an input parameter containing the prepareJSPAttribute parameter value, causing the JSP® page execution to immediately exit without executing user code (i.e., the portion of the code which responds to the user request in generating the dynamic contents). The method  500  then checks whether there are any remaining JSP® pages to be processed at block  532 . If there are remaining JSP® pages to be processed, the method  500  returns to block  518  to process the next JSP® page. When all JSP® pages have been processed, the method  500  ends at block  590 . 
   The method  500  processes all JSP® pages to be loaded for a particular Java® virtual machine based on the initialization parameters prior to receiving a user request. The loaded JSP® page in the Java® virtual machine is ready to be executed when called by a user (client) without the need to be translated, compiled and loaded. Thus, the method  500  substantially reduces the processing time required when an end user requests a JSP® page. When a user (client) requests a JSP® page (either directly or indirectly) which has already been loaded into a Java® virtual machine and ready to be executed, the user does not experience the typical delays. Furthermore, the pre-touch mechanism substantially reduces the delays when an end user requests a JSP® page that calls other JSP® pages. The pre-touch mechanism may also be applied whenever a JSP® page has been modified and need to be translated, compiled and loaded into a Java® virtual machine again. 
   While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.