Abstract:
Disclosed is an apparatus, method, service product, and program product which each provide an enhanced, registration-based event handler mechanism. Listener programs are located and compiled before notification is needed. When notification is ultimately required, the pre-located listeners can be called directly without incurring the performance expense associated with first locating and then calling each listener.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation application of U.S. patent application Ser. No. 12/407,139, filed Mar. 19, 2009, entitled “Mechanism that Provides More Efficient Event Handler Processing”, which is a continuation of U.S. patent application Ser. No. 11/035,553, filed Jan. 14, 2005, entitled “Mechanism that Provides More Efficient Event Handler Processing”, now issued as U.S. Pat. No. 7,519,974 B2, both of which are herein incorporated by reference. This application claims priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 11/035,553, filed Jan. 14, 2005, now issued as U.S. Pat. No. 7,519,974, and U.S. patent application Ser. No. 12/407,139, filed Mar. 19, 2009. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to event handler programs and, more particularly, to the efficiency of the interaction between a base event handler program and individual sub-programs responsible for handling different events. 
       BACKGROUND OF THE INVENTION 
       [0003]    Computer systems are widely used to store and manipulate data. Data is stored in computer system memory and manipulated by computer system programs executing on the computer system&#39;s processor. As is well known, a processor is often thought of as the “brains” of the computer system because it is the component within the computer system that executes the computer system&#39;s programs, allowing the computer system to do real work. Nevertheless, it is really the make-up of computer system&#39;s programs that determines the variety and extent of the work which can be performed. Therefore, while the capabilities of the computer system&#39;s processor are important, the ultimate throughput of a computer system is largely determined by the performance of its programs. For this reason, computer system designers are continually looking for ways to improve program performance. 
         [0004]    One area of focus pertains to programs known in the art as event handlers. Generally speaking, an event handler is a program that receives events from the computer system&#39;s operating system (or other facility), and takes one or more actions based on the particular type of event. A very simple example is that of a printer running out of paper. Many printers will send an event to the computer system when its paper supply has been exhausted. The computer system&#39;s operating system receives this event and forwards it to an event handler. The event handler can then “handle” the event in a manner consistent with its programming. For example, the event handler may post a message to the user or system administrator and/or the event handler may cause the computer system to sound an alarm or beep. Some event handlers, particularly older designs, are monolithic in that they are specifically written to take one or more actions based upon a particular received event. The problem with this approach is the lack of flexibility. I.e., the event handler must be rewritten whenever a new event requires handling or whenever a new action is required. 
         [0005]    In recognition of this flexibility issue, more modern event handlers have what are referred to as “registration interfaces,” which permit sub-programs to register for notification of the receipt of an event. By “sub-programs” we refer to smaller scope programs that typically have a subservient role relative to a larger program. Examples would include procedures (i.e., as used in procedural languages) and methods (i.e., as used in object-oriented languages). (In object-oriented parlance, these sub-programs are often referred to as listeners or collaborators. We make common use of the term listener in this patent.) Registering is the general act of providing sufficient information to the event handler to permit the event handler to contact the listeners at a later time. Taking the printer example, a listener might register with the event handler such that the event handler will notify it when an “out of paper” event is received. The listener would then be responsible for taking the appropriate action (e.g., a message, beep, or alarm). 
         [0006]    The flexibility gained from this approach, however, is not without cost.  FIG. 1  shows an example design of a prior art event handler. As shown, Event Handler  100  includes a Registration Interface  110 . Listeners, shown on  FIG. 1  as Listeners  115 , then utilize Registration Interface  110  to instruct Event Handler  100  to notify them when particular events (i.e., one of events  105 ) are received. Thus, looking at Dynamic Event Tables  120 ,  130 , and  135 , the reader can see that different events have different listeners requiring notification. For example, receipt of a Type 1 event requires notification of listeners B, E, A, and C; whereas receipt of a Type 3 event requires notification of Listener A. Registration for a given listener includes recording its location in each event table for each event for which it requires notification. Notification is then accomplished by locating the particular listener through the location information stored in the event table and then calling the particular listener. The event tables are said to be dynamic because listeners can be added or removed via Registration Interface  110 . 
         [0007]    With this as background, the flexibility cost alluded to above is attributable to the overhead associated with first locating and then calling each listener. Referring again to receipt of a Type 1 event, Event Handler  100  must first find and call (i.e., invoke) Listener B, then Listener E, then Listener A, then Listener C. Locating listeners before invoking them is quite costly from a performance perspective. Of course, full appreciation of this problem&#39;s magnitude becomes more clear when we point out that there may be tens or hundreds of listeners registered for notification of any one event. Therefore, while modern event handlers are more flexible in that event handling capability can be added through registration, the promise of this approach is limited by the performance penalty associated with locating the multiple listeners before calling them. 
         [0008]    Without a mechanism to provide efficient registration-based event handling, the industry will continue to be faced with the choice between older, inflexible event handler designs and newer inefficient ones. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention involves an apparatus, method, and program product which provides an enhanced, registration-based event handler mechanism. The method used in the preferred embodiments of the present invention involves locating and compiling each set of sub-programs before notification is needed. Then, when notification is ultimately required based upon receipt of a given event, the sub-program can be called directly without bearing the expense associated with first locating and each sub-program. Also provided by the present invention is a mechanism for creating the above-described enhanced, registration-based event handler. 
         [0010]    The preferred embodiments of the present invention can both be implemented through use of a virtual machine. By virtual machine, we mean the well-known concept of providing an abstract (i.e., virtual) machine interface that is architecturally above a real (i.e., processor hardware) interface. As is well-understood, this approach permits programs to be written to work against the abstract interface provided by the virtual machine instead of against the actual interface provided by the processor hardware. The benefit to this approach is, of course, the ability to use the same programs on different hardware platforms that include the same virtual machine interface. The first preferred embodiment of the present invention utilizes the Java® Virtual Machine (referred to hereafter as JVM) architecture from Sun Microsystems®. The second preferred embodiment of the present invention utilizes the Common Language Runtime (CLR) of the .NET® framework, both from Microsoft Corporation®. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows an example design of a prior art event handler. 
           [0012]      FIG. 2  is a block diagram showing a computing environment that is capable of supporting the preferred embodiments of the present invention. 
           [0013]      FIG. 3  is a block diagram showing the virtual machine environment used in the preferred embodiments of the present invention. 
           [0014]      FIG. 4  is a block diagram showing an expanded view of the virtual machine architectures used in the preferred embodiments of the present invention. 
           [0015]      FIG. 5  is a flow diagram showing highlighted steps used to carry out the Call Back Optimizer of the preferred embodiments of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    Turning now to the remaining drawings,  FIG. 2  shows some of the operational components used in the computing environment of the preferred embodiment of the present invention. Computer system  200  is an enhanced IBM iSeries computer system, although other computer systems could be used. Depicted components include: Main Memory  205 , Processor  210 , Mass Storage  215 , Network Interface  220 , and User Interface  225 . Processor  210  is a Power PC processor used in iSeries computer systems, which is used in the preferred embodiments in the conventional way. Main Memory  205  is also used in the preferred embodiments in the conventional manner. Mass Storage  215  is used in  FIG. 2  to represent one or more secondary storage devices such as magnetic or optical media. Network interface  220  is used to communicate with other computer systems, while User Interface  225  is used to accept commands and relay information to the one or more users of Computer System  200 . 
         [0017]    Shown within Main Memory  205  is Operating System  206 . Operating System  206  is that known in the industry as IBM i5/OS. Shown utilizing Operating System  206  are Applications  207 , Event Handler  208 , and Virtual Machine  209 . Applications  207  are programs that make use of the facilities provided by Event Handler  208  and Virtual Machine  209 . Event Handler  208 , which is explained in more detail in subsequent paragraphs, is responsible for receiving and handling events generated by Applications  207  or by some other facility. It should be noted, however, that while Event Handler  208  is shown and described herein as a separate entity, it could well be incorporated into Operating System  206 , one or more of Applications  207 , Virtual Machine  209 , or into some other facility. Virtual Machine  209  provides an abstraction layer and runtime environment for Applications  207 , and potentially any of the other facilities and programs associated with Computer System  200 . As stated above, the first preferred embodiment of the present invention utilizes the JVM virtual machine, while the second preferred embodiment utilizes the CLR virtual machine. 
         [0018]    It should be noted that while the inventors have set forth a specific hardware platform within this specification, the present invention and the preferred embodiments should be considered fully applicable to other platforms. It should be further understood that while the embodiments of the present invention are being described herein in the context of a complete system, the program mechanisms described (e.g., Event Handler  208  and Virtual Machine  209 ) are capable of being distributed in program product form. Of course, a program product can be distributed using different types of signal bearing media, including, but not limited to: recordable-type media such as floppy disks, CD ROMs, and memory sticks; and transmission-type media such as digital and analog communications links. 
         [0019]    It should also be understood that embodiments of the present invention may be delivered as part of a service engagement with a client company, nonprofit organization, government entity, internal organizational structure, or the like. Aspects of these embodiments may include configuring a computer system to perform, and deploying software systems and web services that implement, some or all of the methods described herein. Aspects of these embodiments may also include analyzing the client company, creating recommendations responsive to the analysis, generating software to implement portions of the recommendations, integrating the software into existing processes and infrastructure, metering use of the methods and systems described herein, allocating expenses to users, and billing users for their use of these methods and systems. 
         [0020]      FIG. 3  is a block diagram showing a high-level view of the virtual machine environment used in the preferred embodiments. Programs, such as Applications  207  and Event Handler  208  are presented in source code form [block  300 ] to a compiler. For the purposes of this patent, the transformations undergone by Event Handler  208  are at issue. In the first preferred embodiment, the compiler of block  305  is that known in the industry as the Java Compiler, again from Sun Microsystems®. In the second preferred embodiment, the compiler represented by block  305  is that known in the industry as the .Net Compiler, from Microsoft Corporation®. The compilers of block  305  compile the source code of Event Handler  208  into an intermediate representation, which is represented on  FIG. 3  as block  310 . In the first preferred embodiment, this intermediate representation is that known in the industry as Java byte codes, again from Sun Microsystems®, while in the second preferred embodiment the intermediate representation is known as Microsoft Intermediate Language (MSIL). 
         [0021]    At this point, the reader should note that Event Handler  208  can be utilized on other platforms (i.e., having the same virtual machine type—Java or CLR in the preferred embodiments) which do not include the enhancements of the present invention. Said another way, the applicability of Event Handler  208  to other platforms is not diminished because of the enhancements of the preferred embodiments. Continuing with this point, the intermediate representation of Event Handler  208  is compiled into native instructions by Native Compiler  320  (referring to  FIG. 3 ) and it is Native Compiler  320  that provides/contains the enhancements of the preferred embodiments. Thus, the intermediate representation of Event Handler  208 , not having undergone native compilation, is still fully usable on other virtual machines of the same type. Once compiled, Event Handler  208  can be executed on Processor  208 . Interpreter  315  can also be used to convert a program&#39;s intermediate representation in a native one. While it would be possible to incorporate the benefits and advantages of the present invention into Interpreter  315 , the focus here is on Native Compiler  320 . 
         [0022]    Referring now to  FIG. 4 , shown is an expanded view of the virtual machine architectures used in the preferred embodiments of the present invention. It should be noted that we have characterized the basic virtual machine functions in generic terms so as to be applicable to both a Java implementation and a CLR implementation. Semantic differences and functional divisions aside, the majority of the functions and steps shown in the exploded view of Virtual Machine  208  are present in the standard versions of the Java and CLR virtual machines. As stated earlier, the enhancements of the present invention are made in the native compilers (shown as Native Compiler  320 ) of the preferred embodiments. However, other functions are also presented here for completeness. 
       Base Class Library Support  400   
       [0023]    The Base Class Library Support  400  is a standard set of Application Programming Interfaces (APIs) that allow for an application to have access to commonly used data structures and methods. This support is common across all implementations of the JVM and CLR. 
       Thread Support  405   
       [0024]    Thread Support  405  is used to provide Applications  207  with the ability to perform tasks in parallel by executing on multiple threads. This area of the Virtual Machine  208  provides method calls and access to specific thread related method and data structures to control application execution. 
       Type Checker  410   
       [0025]    Type Checker  410  ensures that data being assigned to different pointers or being manipulated in methods (for example mathematical methods, or text processing) is of the same data type to ensure program correctness. 
       Communication Support  415   
       [0026]    Communication Support  415  is the interface to the communication subsystem of Computer System  200 . This allows for applications running on Virtual Machine  208  to access other computer systems or to broadcast messages across a network. 
       Security Engine  420   
       [0027]    Security Engine  420  allows for applications to be implemented in a secure manner on the Virtual Machine  208 . This engine controls access to specific areas of code and ensure tamper free execution. This area also interfaces with the security engine of Operating System  206  to provide features such as password verification and resource access verification. 
       Exception Handler  425   
       [0028]    Exception Handler  425  allows for Virtual Machine  208  to catch user program errors and allow them to exit gracefully without destroying the system runtime as well as gather information from the error to allow the programmer to debug and fix the error. 
       Code Manager  430   
       [0029]    Code Manager  430  is the mechanism in Virtual Machine  208  that manages access to the byte code or MSIL to ensure it is passed to the JIT effectively and compiled to native code when needed. It also controls loading of classes via the Classloader  440 . 
       Garbage Collector  435   
       [0030]    The Garbage Collector  435  manages object clean up inside of the memory space of Virtual Machine  208 . This mechanism removes unused objects from the memory space, compacts objects that still have references to them, and returns a range of available memory to the Virtual Machine  208  for future object allocation. 
       Interpreter  315   
       [0031]    Interpreter  315  is the mechanism that executes the Java byte code or MSIL directly without compiling it to native code via the JIT. This allows for infrequently used code to be executed without being compiled to native code if not necessary. 
       Class Loader  440   
       [0032]    Class Loader  440  is the mechanism that allows for byte codes to be loaded into memory from their repository on the system disks. This allows for dynamic loading of the byte code/MSIL into memory when it is needed by Applications  207  and not before. 
         [0033]    Still referring to  FIG. 4 , an exploded view of Native Compiler  320  will now be presented. It should be noted that within the preferred embodiments (i.e., Java and CLR) Native Complier  320  is referred to as the Just In Time compiler or JIT compiler for short. The blocks shown in the exploded view of Native Compiler  320  represent the compilation steps. While a new step (shown as Call Back Optimizer step  445 ) has been added, other steps are shown here for completeness. 
         [0034]    The Flow Analysis step involves statistically analyzing the code executing in Virtual Machine  208  (initially all code executed is interpreted) and then marking the most frequently executed methods and files in the byte code/MSIL for compilation to native code. Optimization is done here as well as the flow of the program is inspected and dead code is removed, loops are unrolled, etc. 
         [0035]    The Method Inlinig step involves finding the most frequently accessed methods between classes and attempting to insert the to-be-called method directly into the caller method thus optimizing performance by eliminating the calling of the method and associated overhead of Operating System  206 . 
         [0036]    Exception Check Elimination involves analyzing programs that are to be executed on Virtual Machine  208  to determine whether one or more exception handlers can be removed, and if they can, doing so. 
         [0037]    Common Subexpression Elimination involves removing redundant or repeated subexpressions in methods to optimize the method so that it does not perform repeated or unnecessary execution. It also optimizes out expressions that can be executed once for the length of the runtime then cached for future execution of the wrapping method 
         [0038]    Logging/Versioning involves marking loaded byte codes based on the number of passes the Flow Analysis engine has passed over it to keep track of the possibility of further improvement if necessary. 
         [0039]    Stack Analysis involves introspection on Virtual Machine  208 &#39;s stack to make sure memory usage is as optimal as possible and the stack is operating as efficiently as possible. 
         [0040]      FIG. 5  is a flow diagram showing highlighted steps used to carry out the Call Back Optimizer of the preferred embodiments of the present invention. In block  500 , Call Back Optimizer  445  inspects the intermediate representation of Event Handler  208  to identify each event structure (see Event Tables of  FIG. 1 ) handled by Event Handler  208 . The event structures are then processed one by one. The first step is to remove the location identifier for each registered listener from the dynamic event structure and place it in a stack structure for later processing [block  505 ]. In the preferred embodiments, the event structure is the ArrayList structure, having objects stored therein. Thus the objects are removed from the ArrayList structure and stored in the stack structure. 
         [0041]    After the stack structure has been created in block  505 , Call Back Optimizer  445  traverses the stack using reflection on each object to gain access to its method calls (i.e., direct call statements). The method calls are then statically linked into the newly generated code segment [block  510 ]. This step thus inserts direct calls to each listener into Event Handler  208 . The processing of blocks  505  and  515  is then repeated for each event structure [block  515 ]. After all of the event structures have been processed, Native Compiler  320  proceeds to native code generation. Returning briefly to  FIG. 4 , Native Code Generation follows the Call Back Optimizer steps. It is in this phase that the executable version of Event Handler  208  is created. Once made into executable form, Event Handler  208  can be scheduled for execution. 
         [0042]    When Event Handler  208  does run on processor  210  (i.e., in this optimized form), its performance will be markedly improved because each listener can be called directly without the overhead of first determining its location. Production level testing has shown a 14% improvement in overall performance. 
         [0043]    The embodiments and examples set forth herein were presented in order to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and use the invention. However, those skilled in the art will recognize that the foregoing description and examples have been presented for the purposes of illustration and example only. Thus, the description as set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching without departing from the spirit and scope of the following claims.