CN102202242A - Realization method of JavaScript interpreter based on set-top box browser - Google Patents

Abstract

The invention discloses a JavaScript interpreter implementation method based on a set-top box browser. The method of the invention includes: the interpreter system includes an interpreter front end, an interpreter back end and an interpreter execution control module. The interpretation front-end includes a lexical analyzer module, a syntax analyzer module, a source file module, an error handling module, and an intermediate code generation module; the interpretation back-end includes an execution stack module, an object library module, a clause interpreter module, an expression specification module, and an object Interpretation module, browser interaction module, system resource management module, etc. The interpreter of the present invention can quickly and efficiently execute the JavaScript language embedded in the webpage in the embedded browser, and improves the real-time, dynamic and interactive properties between the embedded browser and users. It can effectively reduce the large-scale use of small memory blocks, improve the memory utilization rate, and the effect is good.

Description

Implementation method of JavaScript interpreter based on set-top box browser

technical field

The invention relates to the technical field of digital home, in particular to a JavaScript interpreter implementation method based on a set-top box browser.

Background technique

An important function of digital TV is to realize the conditional access function: the set-top box is also a terminal based on the Internet, therefore, a means of platform payment is needed. In order to support platform payment, JavaScript needs to expand its built-in function library to provide functions related to platform payment, such as deduction function, terminal message signature function, etc. In addition, with the deployment of digital TV, set-top boxes will enter people's homes on a large scale, which requires strict control of the cost of set-top boxes. Therefore, the configuration of the set-top box will be very low. The common configuration of the digital TV set-top box on the market is 4M Flash, 16M memory, and the main frequency of CPU processing is about 130M (many high-frequency products have appeared recently). The requirements are very high. Generally speaking, the embedded browser of the digital TV set-top box is required to occupy less than 6M of memory during operation, and the code size is less than 1M. The configuration of the IPTV set-top box will be relatively higher than that of the digital TV set-top box, so that the embedded browser will have more room to play. In terms of performance, according to the characteristics of embedded systems, it is required to have high interpretation efficiency and convenient expansion of JavaScript support; at the same time, it is required to have as little cross-over as possible with the browser so that the JavaScript interpretation engine can be developed in the form of plug-ins.

During the research and practice of this method, the inventor of the present invention found that the interpreter of the present invention can quickly and efficiently execute the JavaScript language embedded in the webpage in the embedded browser, which improves the interaction between the embedded browser and the user. real-time, dynamic and interactive. It can effectively reduce the large-scale use of small memory blocks, improve the memory utilization rate, and the effect is good.

Contents of the invention

The technical problem to be solved by the present invention is to provide a JavaScript interpreter implementation method based on a set-top box browser, which can quickly and efficiently execute the JavaScript language embedded in the webpage in the embedded browser, and improve the real-time interaction between the embedded browser and the user. Sexuality, dynamicity and interactivity. It can effectively reduce the large-scale use of small memory blocks and improve memory utilization.

A JavaScript interpreter implementation method based on a set-top box browser is characterized in that: the interpreter system includes an interpreter front end, an interpreter back end and an interpreter execution control module. Interpretation front-end includes lexical analyzer module, syntax analyzer module, source file module, error handling module, intermediate code generation module; interpretation back-end includes execution stack module, object library module, clause interpreter module, expression specification module, object Explanation module, browser interaction module, system resource management module; among them,

The lexical analyzer module reads the source program as a character string and divides it into several tokens, which are similar to words in natural language. We classify the words of the JavaScript language into identifiers, strings, integers, floats, booleans, operators, etc. After the source program undergoes lexical analysis, a word doubly linked list is generated for calling by the subsequent syntax analyzer module.

The syntax analyzer module takes the word linked list as input, calls different sentence recognizers respectively, recognizes whether they conform to the given grammar, and finally generates an intermediate code with a syntax tree structure, which will be executed by the later interpretation and execution control module.

The intermediate code generating module is to generate the result of the source program after lexical analysis and syntax analysis as an intermediate result. It includes two aspects of program flow structure and data dictionary. The program flow structure contains various statement structures. The data dictionary is used to store program data. It refers to the collection of stored global variables, local variables in subprograms and local variables in compound statements. The data dictionary is used by the expression reduction module to find the required data during the reduction process.

Interpretation and execution control module The interpretation and execution controller is responsible for interpreting and executing the source program statements one by one according to the semantics of the statement according to the pre-generated intermediate data structure. It controls the sequential execution of the program. During the execution process, the statement interpreter is called to interpret and execute a single statement, and control the continuation or termination of the program according to the interpretation result.

The execution stack module is the data structure used by the expression reduction module. It includes a symbol stack and an operand stack, which are used to store terminal symbols and operands in the expression reduction process.

The object library module is also used to store program data, which refers to the stored system-defined objects,

A collection of objects in the browser's document model and user-defined objects. The object library provides the operating basis for the object interpretation of the interpreter, and also provides the operating mechanism for the interaction between the interpreter and the browser. It contains the properties of the object, methods and event processing and other aspects of the content.

The error handling module is responsible for dealing with lexical analysis, syntax analysis and explaining errors that occur during execution.

Error, if the lexical syntax of the source program does not conform to the rules of the JavaScript language, or an error occurs during execution, it will record the currently executed statement and return immediately.

The clause interpreter module completes the interpretation and execution of a single statement. Each type of statement corresponds to a statement interpreter. It completes the corresponding semantic action according to the statement type. The clause interpreter calls the expression reduction module to calculate the value of the expression during the interpretation process, and controls the flow of the statement according to the calculation result.

The expression reduction module completes the operation of various expressions that make up the statement during the execution of the statement. The expression reduction module finds sub-expressions according to the production rules of the expression and performs reduction to finally obtain the operation result of the expression.

The object interpretation module implements the object-based features of the JavaScript language, which includes object references, method calls, and event processing. In the process of object interpretation, the interpreter completes the interaction with the browser through the change of object property value, object method call or event processing. The interactive module with the browser completes the interpretation and execution of the script program to produce side effects on the web page, modifies the properties of the browser object, and affects or changes the output display of the browser. For example, it causes the position of the control in the web page to change, triggers the submission of the form in the web page, and so on.

System resource management module System resource management acts on the entire interpreter, allocates and recycles memory resources used by the interpreter, and controls CPU resources reasonably.

In the design of the explanation front end, the syntax analyzer module is logically higher than the lexical analyzer module and the semantic action components, and adopts the strategy of "ready-to-use" to save the memory overhead of intermediate data structures such as word linked lists.

The interpreter's backend system is actually a virtual machine that interprets custom bytecode. The back-end virtual machine system is composed of five parts: bytecode interpretation control program and function call relation stack, operand stack, variable data stack and object information record table.

Wherein, the bytecode byte control program operates on the operand according to the operator code of the bytecode, such as stacking and popping. The function call relationship stack records the mutual call relationship of various JavaScript executable codes. Whenever a new executable code is entered, the execution context information of the current executable code is pushed on the top of the function call relationship stack. The operand stack is mainly used for various calculations and storage of intermediate results. All calculations of the intermediate bytecode are performed based on it. The variable data stack is used to record variable information during bytecode execution. Whenever a new executable code is entered, the local variable information (including variable name, type, value, etc.) of the current executable code is pushed into the variable data stack. Once the current executable code is executed, the top element of the variable data stack That is, it is popped up, and the relevant elements in the function call relation stack and the operand stack are popped up at the same time. The object information record table is a memory area that stores various JavaScript objects. Due to the limited available memory resources of the mobile phone middleware platform and the insufficient utilization of small memory blocks, the fixed-length structure array is used as the object information record table. The records in the object record table include the number of attributes of the object, the attribute information of the object, and so on. In JavaScript, methods of an object are also considered properties of the object.

It can be seen from the foregoing technical scheme that the present invention has the following beneficial effects:

The interpreter of the present invention can quickly and efficiently execute the JavaScript language embedded in the webpage in the embedded browser, and improves the real-time, dynamic and interactivity between the embedded browser and the user. It can effectively reduce the large-scale use of small memory blocks, improve the memory utilization rate, and the effect is good.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a system structure diagram of a JavaScript interpreter implementation method based on a set-top box browser of the present invention;

Fig. 2 is a kind of lexical analyzer module structural diagram of the JavaScript interpreter implementation method based on set-top box browser of the present invention;

FIG. 3 is a structural diagram of a syntax analyzer module of a method for implementing a JavaScript interpreter based on a set-top box browser in the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

An embodiment of the present invention provides a method for implementing a JavaScript interpreter based on a set-top box browser, which will be described in detail below.

As shown in Figure 1, the interpreter system includes an interpreter front end, an interpreter back end, and an interpreter execution control module. The interpretation front-end includes a lexical analyzer module, a syntax analyzer module, a source file module, an error handling module, and an intermediate code generation module; the interpretation back-end includes an execution stack module, an object library module, a clause interpreter module, an expression specification module, and an object Explanation module, interaction module with browser, system resource management module;

Among them, the lexical analyzer module reads the source program in the form of character strings and divides it into several tokens, which are similar to words in natural language. We classify the words of the JavaScript language into identifiers, strings, integers, floats, booleans, operators, etc. After the source program undergoes lexical analysis, a word doubly linked list is generated for calling by the subsequent syntax analyzer module.

The syntax analyzer module takes the word linked list as input, calls different sentence recognizers respectively, recognizes whether they conform to the given grammar, and finally generates an intermediate code with a syntax tree structure, which will be executed by the later interpretation and execution control module.

The intermediate code generating module is to generate the result of the source program after lexical analysis and syntax analysis as an intermediate result. It includes two aspects of program flow structure and data dictionary. The program flow structure contains various statement structures. The data dictionary is used to store program data. It refers to the collection of stored global variables, local variables in subprograms and local variables in compound statements. The data dictionary is used by the expression reduction module to find the required data during the reduction process.

Interpretation and execution control module The interpretation and execution controller is responsible for interpreting and executing the source program statements one by one according to the semantics of the statement according to the pre-generated intermediate data structure. It controls the sequential execution of the program. During the execution process, the statement interpreter is called to interpret and execute a single statement, and control the continuation or termination of the program according to the interpretation result.

The execution stack module is the data structure used by the expression reduction module. It includes a symbol stack and an operand stack, which are used to store terminal symbols and operands in the expression reduction process.

The object library module is also used to store program data, which refers to the stored system-defined objects,

A collection of objects in the browser's document model and user-defined objects. The object library provides the operating basis for the object interpretation of the interpreter, and also provides the operating mechanism for the interaction between the interpreter and the browser. It contains the properties of the object, methods and event processing and other aspects of the content.

The error handling module is responsible for dealing with lexical analysis, syntax analysis and explaining errors that occur during execution.

Error, if the lexical syntax of the source program does not conform to the rules of the JavaScript language, or an error occurs during execution, it will record the currently executed statement and return immediately.

The clause interpreter module completes the interpretation and execution of a single statement. Each type of statement corresponds to a statement interpreter. It completes the corresponding semantic action according to the statement type. The clause interpreter calls the expression reduction module to calculate the value of the expression during the interpretation process, and controls the flow of the statement according to the calculation result.

The expression reduction module completes the operation of various expressions that make up the statement during the execution of the statement. The expression reduction module finds sub-expressions according to the production rules of the expression and performs reduction to finally obtain the operation result of the expression.

The object interpretation module implements the object-based features of the JavaScript language, which includes object references, method calls, and event processing. In the process of object interpretation, the interpreter completes the interaction with the browser through the change of object property value, object method call or event processing. The interactive module with the browser completes the interpretation and execution of the script program to produce side effects on the web page, modifies the properties of the browser object, and affects or changes the output display of the browser. For example, it causes the position of the control in the web page to change, triggers the submission of the form in the web page, and so on.

System resource management module System resource management acts on the entire interpreter, allocates and recycles memory resources used by the interpreter, and controls CPU resources reasonably.

In the design of the explanation front end, the syntax analyzer module is logically higher than the lexical analyzer module and the semantic action components, and adopts the strategy of "ready-to-use" to save the memory overhead of intermediate data structures such as word linked lists.

The interpreter's backend system is actually a virtual machine that interprets custom bytecode. The back-end virtual machine system is composed of five parts: bytecode interpretation control program and function call relation stack, operand stack, variable data stack and object information record table.

Wherein, the bytecode byte control program performs operations on operands, such as stacking and popping, according to the operator code of the bytecode. The function call relationship stack records the mutual call relationship of various JavaScript executable codes. Whenever a new executable code is entered, the execution context information of the current executable code is pushed on the top of the function call relationship stack. The operand stack is mainly used for various calculations and storage of intermediate results. All calculations of the intermediate bytecode are performed based on it. The variable data stack is used to record variable information during bytecode execution. Whenever a new executable code is entered, the local variable information (including variable name, type, value, etc.) of the current executable code is pushed into the variable data stack. Once the current executable code is executed, the top element of the variable data stack That is, it is popped up, and the relevant elements in the function call relation stack and the operand stack are popped up at the same time. The object information record table is a memory area that stores various JavaScript objects. Due to the limited available memory resources of the mobile phone middleware platform and the insufficient utilization of small memory blocks, the fixed-length structure array is used as the object information record table. The records in the object record table include the number of attributes of the object, the attribute information of the object, and so on. In JavaScript, methods of an object are also considered properties of the object.

As shown in Figure 2, the processing flow of the lexical analyzer module is: when the lexical analyzer calls the preprocessing subroutine to eliminate useless editing text such as spaces, tabs, carriage returns, and line feeds, a string of input characters is processed and put into the scan buffer After that, the scanner recognizes word symbols one by one from the buffer. When the string in the buffer is processed, it calls the preprocessor to load the new string.

As shown in Figure 3, the processing flow of the syntax analyzer module is: taking the word symbol doubly linked list generated by lexical analysis as input, analyzing the source program statements one by one according to the syntax analysis method, and finally generating the source program statement flow chart and data dictionary . During the execution, the statement recognizer is called to identify different kinds of statements, and at the same time, a data dictionary is also generated for the interpretation and execution control module to use for the expression specification.

The sentence recognizer completes the recognition of a single sentence, and there is a sentence recognizer corresponding to different types of sentences. Sentence recognizer recognizes sentences according to the grammatical rules and semantics of the sentence. The data dictionary is the place where program data is stored, including global variables, function parameter variables, and local variables in statement blocks. The data dictionary is used for the expression specification module of the interpretation execution module to find the required data when performing expression specification.

It should be noted that, since the information interaction and execution process between the above-mentioned devices and units in the system are based on the same idea as the method embodiment of the present invention, the specific content can refer to the description in the method embodiment of the present invention, here No longer.

Those of ordinary skill in the art can understand that all or part of the steps in the various methods of the above-mentioned embodiments can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable storage medium, and the storage medium can include: Read Only Memory (ROM, Read Only Memory), Random Access Memory (RAM, Random Access Memory), disk or CD, etc.

The implementation method of a JavaScript interpreter based on a set-top box browser provided by the embodiment of the present invention has been introduced in detail above. In this paper, specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only It is used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation and scope of application. In summary, this The content of the description should not be construed as limiting the present invention.

Claims (3)

1. a JavaScript interpreter implementation method based on a set-top box browser, is characterized in that: the interpreter system includes explaining the front end and explaining the back end and explaining the execution control module, and explaining that the front end includes a lexical analyzer module, a syntax analyzer module, a source file modules, error handling modules, and intermediate code generation modules; the interpretation backend includes execution stack modules, object library modules, clause interpreter modules, expression specification modules, object interpretation modules, browser interaction modules, and system resource management modules; Among them, the lexical analyzer module reads the source program in the form of strings and divides them into several tokens, which are similar to words in natural languages; we divide JavaScript language words into identifiers, strings, and integers. , floating-point numbers, Boolean values, operators, etc.; the source program generates a word doubly linked list after lexical analysis, which is called by the subsequent syntax analyzer module; The grammatical analyzer module takes the word linked list as input, calls different sentence recognizers respectively, recognizes whether they conform to the given grammar, and finally generates an intermediate code of a grammatical tree structure, which will be executed by the later interpretation and execution control module; The intermediate code generation module is to generate the result of the source program after lexical analysis and syntax analysis as an intermediate result. It includes two aspects: the program flow structure and the data dictionary. The program flow structure includes various sentence structures, and the data dictionary is The place used to store program data, which refers to the collection of stored global variables, local variables in subprograms and local variables in compound statements; the data dictionary is used for the expression reduction module to find what it needs during the reduction process data, Interpretation and execution control module The interpretation and execution controller is responsible for interpreting and executing the source program statements one by one according to the semantics of the statement according to the pre-generated intermediate data structure. It controls the sequential execution process of the program; during the execution process, the statement interpreter is called to interpret and execute a single statement , and control the continuation or termination of the program according to the result of the interpretation; The execution stack module is the data structure used by the expression reduction module, which includes a symbol stack and an operand stack, which are used to store terminal symbols and operands in the expression reduction process; The object library module is also used to store program data, which refers to the stored system-defined objects, A collection of objects in the browser document model and user-defined objects; the object library provides the operating basis for the interpreter's object interpretation, and also provides an operating mechanism for the interaction between the interpreter and the browser; it includes object properties, Methods and event handling, etc.; The error handling module is responsible for dealing with lexical analysis, syntax analysis and explaining errors that occur during execution. Error, if the lexical syntax of the source program does not conform to the rules of the JavaScript language, or an error occurs during execution, record the currently executed statement and return immediately; The clause interpreter module completes the interpretation and execution of a single statement; each type of statement corresponds to a statement interpreter; it completes the corresponding semantic action according to the statement type; the clause interpreter calls the expression reduction module to calculate during the interpretation process The value of the expression, and control the statement flow according to the calculation result; The expression reduction module completes the calculation of various expressions that make up the statement during the execution of the statement; the expression reduction module finds out sub-expressions according to the production rules of the expression and performs reduction to finally obtain the operation result of the expression; The object interpretation module implements the object-based features of the JavaScript language, which includes object references, method invocations, and event processing; in the process of object interpretation, the interpreter communicates with the browser through changes in object attribute values, object method invocations, or event processing. Interaction; interacting with the browser module to complete the interpretation and execution of the script program, the side effects on the web page, modify the properties of the browser object, and affect or change the output display of the browser; System resource management module System resource management acts on the entire interpreter, allocates and recycles memory resources used by the interpreter, and controls CPU resources reasonably. 2. a kind of JavaScript interpreter implementation method based on set-top box browser according to claim 1, is characterized in that: In the design of the explanation front end, the syntax analyzer module is logically higher than the lexical analyzer module and the semantic action components, and adopts the strategy of "ready-to-use" to save the memory overhead of intermediate data structures such as word linked lists. 3. a kind of JavaScript interpreter implementation method based on set-top box browser according to claim 1, it is characterized in that: the backend system of interpreter is actually a virtual machine that explains self-defined bytecode, and the backend virtual machine The system is composed of bytecode interpretation control program and function call relation stack, operand stack, variable data stack and object information record table; Among them, the bytecode byte control program operates on operands according to the bytecode operator code, such as stacking and popping, etc.; the function call relationship stack records the mutual calling relationship of various JavaScript executable codes. When entering a new executable code, push the execution context information of the current executable code on the top of the function call relationship stack; the operand stack is mainly used for various calculations and storage of intermediate results, and the intermediate bytecode All calculations are based on it. The variable data stack is used to record the variable information when the bytecode is executed. Whenever a new executable code is entered, the local variable information of the current executable code is pushed into the variable data stack, including Variable name, type, value, once the current executable code is executed, the top element of the variable data stack will be popped up, and the related elements in the function call relationship stack and operand stack will be popped up at the same time; the object information record table is used to store various JavaScript objects Memory area; due to the limited available memory resources of the mobile middleware platform and the insufficient utilization of small memory blocks, a fixed-length structure array is used as the object information record table; the records in the object record table include the number of attributes of the object and the attributes of the object Information, etc.; in JavaScript, the method of the object is also regarded as the property of the object.

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