Abstract:
A solution to avoid performance degradation associated with load-object independence by arranging interface source code, particurlarly JNI source code, in a stylized form, and then preprocessing the stylized interface source code into a Virtual Machine (“VM”) specific form. The stylized source code allows a preprocessor to identify and track field and method identifiers, and to match up the field and method uses with the specification of the field or method. The source code is stylized by substituting stylized variable names, each with a native element identifier, for non-stylized variables.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to preprocessing computer source code. More specifically, the invention relates to preprocessing native interface source code.  
           [0002]    Java is an object-oriented computer programming language. It is most commonly used in Internet applications where Java programs are called from within HTML documents. However, Java programs can also be launched as stand alone applications.  
           [0003]    Before it is executed, Java source code is usually translated or compiled into byte code by a Java compiler. The byte code is then interpreted or converted to machine language at run time. Java can be implemented as an interpreted language, meaning programs written in Java can be run using an interpreter. An interpreter translates and runs a program at the same time. Specifically, the interpreter translates one line of programming, executes that line of code, and then proceeds to the next line of code.  
           [0004]    The Java Virtual Machine (“VM”) carries out the task of interpreting or otherwise executing the Java byte code. Java VMs are present in most browsers and widely licensed for use in a variety of computing devices. In fact, Java VMs are so widely distributed that Java is said to offer “write once, run anywhere” portability. With most other programming languages, different versions of a program must be developed for different computer environments. Further, Java programs can be stored in relatively small files, which is important in applications where memory is limited (e.g., when running software on cell phones, personal digital assistants, and the like) and makes transmitting the programs over networks easier and faster.  
           [0005]    While it is possible to create a computing environment specifically designed for Java (e.g., by using a Java chip), most Java platforms are deployed on top of a non-Java host environment that employs a standard processor with a Java VM installed in memory. A Java platform is a programming environment that includes the Java VM and the Java application programming interface (“API”). The Java API consists of a set of predefined classes.  
           [0006]    Java also includes a programming interface known as the Java Native Interface (“JNI”). The JNI provides a mechanism for calling native platform elements such as graphical user interface (“GUI”) routines and integrating legacy software (existing code written in languages other than Java) in a Java application. As is known, a native application is one specifically designed to run on the computing environment at hand (the operating system and machine language for particular hardware). The JNI allows Java elements incorporating or referencing native methods to be written and compiled in such a way that the resulting load object is independent of the Java Virtual Machine specifics, and can be used with any virtual machine that supports the JNI for that environment. However, the abstraction that the JNI layer provides to allow load-object independence imposes a performance penalty on both the entry and exit from the native method and also on the activities within the native method, where elements of the Java system such as fields, other methods, etc. need to be accessed from the native method.  
         SUMMARY OF THE INVENTION  
         [0007]    Accordingly, there is a need for an improved method and system for calling native elements using a programming interface, such as the JNI. In particular, there is a need for an improved manner of calling native elements that does not impose performance penalties during execution.  
           [0008]    In one embodiment, the invention provides a solution to performance degradation associated with load-object independence by arranging JNI source code in a stylized form, and then preprocessing the stylized JNI source code into a VM-specific form. The VM-specific form avoids much if not all the extra overhead imposed by standard JNI coding and processing. However, the stylized JNI source code can be built without the preprocessing step as standard JNI source. Therefore, it can be used with a variety of virtual machines.  
           [0009]    The stylized JNI code allows the preprocessor to identify and track field and method identifiers, and to match up the field and method uses with the specification of the field or method. The stylized JNI also allows the Java object references to be tracked for Garbage Collection purposes. The preprocessor changes the name of the preprocessed native methods to allow the native method loading mechanism to distinguish between preprocessed JNI native methods and standard JNI native methods, which the VM may still encounter from third party load units.  
           [0010]    The load unit produced from pre-processing the stylized JNI is tied to a specific VM (and indeed a particular version of that specific VM) due to the implied knowledge of the object layout and the direct access to various VM internal structures and routines.  
           [0011]    As is apparent from the above, it is an advantage of the invention to provide a method and system of arranging JNI source code in a stylized form and then preprocessing that code into a VM-specific form, which reduces the overhead imposed by standard JNI coding and processing. Other features and advantages of the present invention will become apparent by consideration of the detailed description and accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a schematic diagram of the interaction of a JNI with other components in a computing environment.  
         [0013]    [0013]FIG. 2 is a flow diagram showing a typical process of running a Java application that calls a native function.  
         [0014]    [0014]FIG. 3 is a flow diagram illustrating the use of a preprocessor according to one embodiment of the invention.  
         [0015]    [0015]FIG. 4 is a flow chart of the processing that occurs in the preprocessor of one embodiment the invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]    Before embodiments of the invention are explained, it is to be understood that the invention is not limited in its application to the details of the construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The following description assumes that the reader is familiar with computer science and has a working knowledge of Java, C, and assembly programming languages, as one of ordinary skill in the art would possess.  
         [0017]    [0017]FIG. 1 illustrates various components of a computing environment  10 . The environment  10  includes a Java application  12  and an associated library  14  of executable program modules. A Java VM  16  having an interpreter  17  executes the Java application  12 . The Java VM  16  also has a JNI  18 , which interfaces with a native application  20  and an associated native library  22 , which includes executable program modules for the native environment. The Java VM  16  and native application  20  (as compiled to create a dynamic link library, in the example shown) interact with a host environment  24  (the operating system and machine language for the particular hardware used).  
         [0018]    The JNI  18  can be used to write native methods that allow Java applications to call functions implemented in the native library  22 . The JNI  18  also supports an invocation interface that allows the embedding of a Java VM into native applications. For example, a web browser written in the C language can execute downloaded Java applets in an embedded VM.  
         [0019]    [0019]FIG. 2 illustrates a typical process of using the JNI  18  to run a Java application that calls a C function. As shown at step  30 , a Java class (“exampleProg”) that declares a native method is created. The Java class is then compiled at step  34  to generate a class file “exampleProg.class.” At step  38 , the Java header tool is used to create a header file “exampleProg.h.” The C implementation of the native method (“exampleProg.c”) (which could be any method, from a simple method to display text on a display to a complex method) is written at step  42 . Once the native method is written, it is compiled to create a native library “exampleProg.dll,” as shown at step  44 . Finally, the Java program is run with the native library at step  48  to produce some end result or output  50 .  
         [0020]    As was noted above, the JNI allows native methods to access Java items and the Java VM machine. The JNI also allows native methods to be called and parameters to be passed to the native methods. The JNI does this in such a way that object code, as compiled from, for example, a C native method, is binary compatible with a variety of VMs. In order to provide this compatibility, the JNI introduces an abstraction layer, which is implemented through the JNI API set.  
         [0021]    There are a number of factors to the abstraction introduced by the JNI. All the object references that the native method refers to are referred to through a specific type and subtypes of that type. The type is “JNI reference.” This typically adds an extra level of indirection to native objects. When the native method wants to call a service of the VM, the native method calls through a function table, which is passed to the native method via one of the parameters to the native method. One of the native method parameters is a pointer to the JNI environment, and the JNI environment contains a pointer to the function table. Thus, load object compatibility results in multiple cases of indirection to get to a desired function. This allows native elements to operate without knowledge of the VM, but in exchange the JNI adds inefficiency by requiring many reference layers.  
         [0022]    It has been found that if the particular VM that will be used in a particular situation is known and it is acceptable to restrict portability of the compiled JNI code, pre-processing of the native source to change JNI API calls into direct calls or direct macro access that perform operations in line (i.e., in a line of code) enhances efficiency.  
         [0023]    According to one aspect of the invention, JNI code is written in a stylized form so that it is still legal or acceptable JNI syntax. However, the stylized form includes particular stylized names of variables, such as field identifiers and method identifiers. Furthermore, the stylized names include information regarding the use of the method or field. This permits identification of the field or method being referenced at the point in the code where the field or method is being used or called. This, in turn, provides more direct access to the field or method as compared to standard JNI coding.  
         [0024]    Examples of how to code a stylized JNI method and a field are set out below.  
                                                                       NOTATIONS   Code                       jmethodID x;           jclass cl;       Line A:   cl =(*env)→FindClass (env, “myClass”);       Variable x:   x = (*env)→GetMethodID           (env, cl, “getValue,” “(I)V”);           {additional source }       Line B:   (*env)−&gt;CallVoidMethod (env, x, val);                to stylize use variable name myclass_get_value_IV_mID           instead of x                jfieldID f;           jclass cl;           cl=(*env)→FindClass(env, “myClass”);       Line C:   f=(*env)→GetFieldID (env, cl, “value,” “I”);           y=(*env)→GetIntField(env, obj, f);           (*env)→SetIntField (env, obj, f, y+1);                to stylize use myClass value_I_fID instead of f; Line C becomes           myClass_getvalue_I_fID =            (*env)−&gt;GetfieldID(env, cl, “value,” “I”);                  
 
         [0025]    As can be seen by reference to the method code above, when the JNI code is written with a stylized variable name, which contains a method identifier, rather than the variable “x,” the code provides information to the processor, in this case a preprocessor (discussed below), such that when the preprocessor encounters the code it knows what method is actually being called. Thus, the preprocessor can convert the code into a more efficient form. In particular, the preprocessor can convert Line A such that it performs no operation and is able to convert Line B into an instruction that calls a method directly rather than going through the abstraction that JNI ordinarily imposes. A similar improvement is achieved for the field code set out above, where a field identifier is used rather that the variable “f.” 
         [0026]    [0026]FIG. 3. illustrates the process of using preprocessing according to one embodiment of the invention. As shown in FIG. 3, exemplary Java class source “xxx.java” containing a field to be referenced from native code and class source “yyy.java” that contains a method to be referenced from native code are processed in a Java compiler  60  to generate class files “xxx.class” and “yyy.class,” respectively. A stylized native method “nm.c” (as opposed to a non-stylized native application such as exampleProg.c, above) that refers to “xxx” and “yyy” is input to a preprocessor  64 . The class files “xxx.class” and “yyy.class” are also input to the preprocessor  64 . The preprocessor  64  generates targeted C source code, “nm1.c.” The targeted C source code “nm1.c” is then compiled in a C compiler  68 . In the embodiment illustrated, the compiler  68  generates an object file “nm1.o,” which is then linked in a linking process  72  to generate a dynamic link library “nm1.dll.” The library “nm1.dll” can then be used in a manner similar to the library “exampleProg.dll” as shown at step  48  in FIG. 2, where the compiled Java classes referring to or including the native element are executed in the interpreter of the virtual machine.  
         [0027]    The preprocessor  64  is illustrated in greater detail in FIG. 4. Input delivered to the preprocessor  64  may be processed in an optional comment removal module  80 . The comment removal module  80  removes programming comments to make preprocessing of the source code easier. However, the removal of comments is not required. Preferably, the comment removal module  80  also tracks the location of the comments within the source code to assist in re-inserting the comments once preprocessing of the code is complete.  
         [0028]    Following any comment removal, the preprocessor  64  begins the analysis of each line of JNI source code looking for particular patterns, in a line-by-line fashion. The code is delivered to a line analyzer  84  that looks for patterns that match the stylization used in the stylized JNI source, as shown at step  88 . For example, “GetMethodID” would be an applicable pattern for the method code example described above. If the line of code does not contain a pattern of interest then the line analyzer  84  continues searching through the code until all patterns in all the lines have been found as shown in step  92  and by loop  96 . If a pattern is found, then the line analyzer  84  determines whether the preprocessor has knowledge about the applicable class as shown at step  96 . If the preprocessor  64  already knows the identified class, then a translation operation is performed in a translator  100  to convert the stylized code to a translated form with direct access to the relevant class. If the preprocessor does not have knowledge of the relevant class then information regarding that class is loaded from a database  104  of classes by a loading module  108 . The code is then translated in the translator  100 .  
         [0029]    Once all the lines of code have been analyzed and translated as appropriate, the preprocessor re-inserts any comments it removed before the analysis using a comment inserter  112 . Finally, a complete output file  114  including the comments, the JNI code that had no patterns, and the stylized portions of the JNI now in a translated form, is assembled and output by the preprocessor  64 .  
         [0030]    An example of stylized JNI in translated form, for an x86 environment is set out below. The stylized form of the source would be as the last two source lines of the previous field access example:  
         [0031]    y=(*env)→GetIntField(env, obj, myClass_value_I_fID);  
         [0032]    (*env)→SetIntField (env, obj, myClass_value_I_flD, y+1);  
         [0033]    which would be preprocessed to a form such as:  
         [0034]    y=(*((int**)obj))[5];  
         [0035]    (*((int**)obj))[5]=y+1;  
         [0036]    The preprocessed version uses information which is specific to the VM to be used, namely that the real reference value can be obtained from the JNI reference of an object by a single de-reference, and that the “value” field in an object of the particular example class lies at 5 words, i.e. 20 bytes, into the object.  
         [0037]    x86 assembly format as might be produced from the un-preprocessed source  
                                           PUSH   [myClass_value_I_fID]           MOV   EBX, 16 [EBP]   ;env       PUSH   12 [EBP]   ;obj       PUSH   EBX   ;env       MOV   ECX, [EBX]   ;*env       CALL   24[ECX]   ;get “value” field       POP   ECX   ;discard function parameters       POP   ECX       POP   ECX       MOV   32 [EBP], EAX   ;store value as C variable “y”       INC   EAX       PUSH   EAX       PUSH   [myClass_value_I_fID]       PUSH   12 [EBP]   ;obj       PUSH   EBX   ;env       MOV   ECX, [EBX]   ;*env       CALL   50 [ECX]   ;set “value” field       POP   ECX   ;discard function parameters       POP   ECX       POP   ECX       POP   ECX                  
 
         [0038]    X86 assembly format as might be produced from preprocessed source  
                                                           MOV   EAX, 12 [EBP]   ; obj JNI ref           MOV   EAX, [EAX]   ; real ref           MOV   ECX, 20 [EAX]   ; get “value” field           MOV   32 [EBP], ECX   ; store value as C variable “y”           INC   ECX           MOV   20 [EAX], ECX   ; set “value” field                      
 
         [0039]    The example assembly code as produced from un-preprocessed source shows that the majority of the instructions, i.e., the first nine instructions and the last 10 instructions, are to perform two accesses to the “value” field of the object. These instructions prepare the parameters to the JNI API function call by pushing them on the stack, then call the JNI API function, and then discard the parameter values after the function call. Further to the instructions shown in the above example, the processor would need to execute the bodies of the two JNI API routines called to perform the desired operation. Conversely, the second version, as produced from preprocessed source, shows many fewer instructions needing to be executed, and no other routines needing to be called to perform the desired operation.  
         [0040]    In the preparation of both examples, some assumptions have been made as to the layout of the C functions local variables in the functions frame, i.e. that the local variable “y” is stored at 32 bytes from the frame pointer and the “obj” variable is stored at 12 bytes from the frame pointer, which is held in the EBP register. The first version makes other assumptions about the C variable and structure access, such as access to the “env” function parameter and the offsets in the JNI API function vector to call the “GetIntField” and “SetIntField” JNI API functions.  
         [0041]    As can be seen from the above, the invention provides a method and system arranging interface source code in stylized form and then preprocessing that code into a VM-specific form. Various features and advantages of the invention are set forth in the following claims.