jsapigen 0.5
Copyright © 2008, 2009 Thomas ZimmermannPermission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".
| Revision History | ||
|---|---|---|
| Revision 4.0 | 29 Dec 2009 | Revised by: tdz |
| Updates for jsapigen 0.5. | ||
| Revision 3.0 | 13 Apr 2009 | Revised by: tdz |
| Updates for jsapigen 0.4. | ||
| Revision 2.0 | 27 Feb 2009 | Revised by: tdz |
| Updates for jsapigen 0.3. | ||
| Revision 1.0 | 10 Aug 2008 | Revised by: tdz |
| Initial revision. | ||
jsapigen is distributed under the conditions of version 3 of the GNU General Public License. Code that has been generated by jsapigen can be distributed under a license of your choice.
JavaScript is a popular scripting language for web pages. It has been in development since the mid-90s. Dialects of the language have been implemented in various web browsers by different vendors.
The core language and library of JavaScript is completely independent of any browser. This allows for JavaScript to be used as general purpose scripting language.
A standardized version of JavaScript is ECMAScript. The rest of this document uses the more common term JavaScript, even though really talks about ECMAScript instead.
SpiderMonkey is Mozilla's implementation of JavaScript and also acts as reference implementation for JavaScript's further evolution. As of summer 2008 SpiderMonkey supports version 1.8 of JavaScript (version 3 of ECMAScript).
SpiderMonkey's public interfaceis called JSAPI. It allows the embedding of SpiderMonkey in C-based applications. It provides functions to
setup the JavaScript engine,
make function calls into the JavaScript environment, and
make C functions available to JavaScript programs.
A simple JSAPI setup looks like this.
Example 1. The skeleton of embedding SpiderMonkey.
#include <jsapi.h>
#include <stdlib.h>
int
main(int argc, char **argv)
{
static JSClass global_class = {
"global", JSCLASS_GLOBAL_FLAGS,
JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_PropertyStub,
JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, JS_FinalizeStub,
JSCLASS_NO_OPTIONAL_MEMBERS
};
JSRuntime *rt;
JSContext *cx;
JSObject *global;
/* Create an instance of the engine */
rt = JS_NewRuntime(1024*1024);
if (!rt) {
exit(EXIT_FAILURE);
}
/* Create an execution context */
cx = JS_NewContext(rt, 8192);
if (!cx) {
exit(EXIT_FAILURE);
}
/* Create a global object and a set of standard objects */
global = JS_NewObject(cx, &global_class, NULL, NULL);
if (!global) {
exit(EXIT_FAILURE);
}
if (JS_InitStandardClasses(cx, global) != JS_TRUE) {
exit(EXIT_FAILURE);
}
/* Do something */
...
/* Cleanup */
JS_DestroyContext(cx);
JS_DestroyRuntime(rt);
JS_ShutDown();
exit(EXIT_SUCCESS);
}
|
With this skeleton program it is already possible to use SpiderMonkey. For example, one can execute a script file by inserting the following fragment at line 49.
Example 2. Executing a script file.
{
JSScript *script;
jsval rval;
/* Compile a script file into a script object */
script = JS_CompileFile(cx, global, "hello.js");
if (!script) {
exit(EXIT_FAILURE);
}
/* Execute script object */
if (JS_ExecuteScript(cx, global, script, &rval) != JS_TRUE) {
exit(EXIT_FAILURE);
}
/* Remove script object from memory */
JS_DestroyScript(cx, script);
}
|
By default, each JavaScript program runs in its own, isolated environment. To allow interaction with the environment, the programmer has to register native C functions with the JavaScript engine. Such a function looks as follows.
Example 3. A simple native function call.
#include <stdio.h>
static JSBool
hello_world(JSContext *cx, JSObject *obj, uintN argc, jsval *argv, jsval *rval)
{
printf("Hello world!\n");
return JS_TRUE;
}
|
Registering native functions is done before the execution of a script. When the script executes, it can call registered function to interact with the outside program of its JavaScript environment.
Example 4. Defining a function in the JavaScript engine.
{
if (JS_DefineFunction(cx, global, "helloWorld", hello_world, 0, 0) != JS_TRUE) {
exit(EXIT_FAILURE);
}
}
|
For example, the code fragment above registers the function hello_world as a function of the global object. A script can now execute it by calling helloWorld. This outputs the phrase
Hello world! |
to the user's terminal.
This is only a very simple example. With JSAPI, it is possible to create new JavaScript classes, each with its own functions and properties. Complete information can be found at Mozilla's SpiderMonkey website. The programmer can write the program's complete logic in JavaScript and only needs C for interfacing with basic system services. However, this comes at the cost of writing large amounts of glue code. The purpose of jsapigen is to automate the creation of this code.
The problem with JSAPI is that it requires large amounts of repetitive and error-prone glue code. jsapigen is a tool for generating such code automatically.
The first step to automated generation of glue code is to write a C function that provides the basic functionality. For this example, the C function is implemented similarly to hello_world from the previous section. It goes at the beginning of the IDL file and is enclosed by %{ and %}. This section is called prologue. The prologue is copied one-by-one to the output file.
Example 5. Hello world in C
%{
#include <stdio.h>
static void
hello_world(void)
{
printf("Hello world!\n");
}
%}
|
In the next step, the IDL code is implemented. It is placed after the prologue. For this example, there is exactly one function declaration.
The keyword function introduces the declaration of a call from JavaScript to C. It is followed by the function's return type and the function's name within the JavaScript environment. Here the return type is void because the function does not return anything. The JavaScript function's name is js_hello_world. On the right side of the colon is the name of the associated C function, hello_world in this case. It does not take any arguments, so the argument list is omitted here. The right-most part is a list of attributes. The attribute static indicates that the function can be callable without an instance of a class.
The declaration has to be registered with the JavaScript environment via JSAPI. We simple reuse the code from the previous section. All this code goes into a section at the end of the IDL file. it is enclosed by %< and %>, and called epilogue. The complete file looks as follows.
Example 7. A complete example.
%{
#include <stdio.h>
static void
hello_world(void)
{
printf("Hello world!\n");
}
%}
function void js_hello_world : hello_world <static>;
%<
#include <jsapi.h>
#include <stdlib.h>
int
main(int argc, char **argv)
{
static JSClass global_class = {
"global", JSCLASS_GLOBAL_FLAGS,
JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_PropertyStub,
JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, JS_FinalizeStub,
JSCLASS_NO_OPTIONAL_MEMBERS
};
JSRuntime *rt;
JSContext *cx;
JSObject *global;
/* Create an instance of the engine */
rt = JS_NewRuntime(1024*1024);
if (!rt) {
exit(EXIT_FAILURE);
}
/* Create an execution context */
cx = JS_NewContext(rt, 8192);
if (!cx) {
exit(EXIT_FAILURE);
}
/* Create a global object and a set of standard objects */
global = JS_NewObject(cx, &global_class, NULL, NULL);
if (!global) {
exit(EXIT_FAILURE);
}
if (JS_InitStandardClasses(cx, global) != JS_TRUE) {
exit(EXIT_FAILURE);
}
/* Define function */
{
if (JS_DefineFunctions(cx, global, jj_fs) != JS_TRUE) {
exit(EXIT_FAILURE);
}
}
/* Execute a script */
{
JSScript *script;
jsval rval;
/* Compile a script file into a script object */
script = JS_CompileFile(cx, global, "tutorial.js");
if (!script) {
exit(EXIT_FAILURE);
}
/* Execute script object */
if (JS_ExecuteScript(cx, global, script, &rval) != JS_TRUE) {
exit(EXIT_FAILURE);
}
/* Remove script object from memory */
JS_DestroyScript(cx, script);
}
/* Cleanup */
JS_DestroyContext(cx);
JS_DestroyRuntime(rt);
JS_ShutDown();
exit(EXIT_SUCCESS);
}
%>
|
This example IDL file, called tutorial.j, is now given to jsapigen, which outputs corresponding C code. jsapigen by default reads and writes on standard I/O streams. So on Unix-like systems you can run
jsapigen < tutorial.j > tuturial.j.c |
On systems that do not support input redirection well, such as Windows, you can run
jsapigen -f tutorial.j -o tuturial.j.c |
If you are using the GNU C compiler on Linux you can compile the generated file tutorial.j.c to an application by running the following command.
gcc -DXP_UNIX -I/usr/include/mozjs -g3 -o tutorial -lmozjs tutorial.j.c |
It might happen that you have to adjust the include path or the name of the SpiderMonkey library. Sometimes they are called js, mozilla, or something similar.
Now, create a JavaScript-file tutorial.js that contains the following line.
js_hello_world(); |
Executing the compiled application tutorial will output a message on the terminal.
./tutorial
Hello world!
|
What happened is that the application set up SpiderMonkey, registered the generated functions with it, and executed the JavaScript file with the call to js_hello_world. This resulted in a call to the generated glue code and as result in a call to hello_world, which printed the string Hello world! on the user's terminal.
The next step is to add a function with arguments. For this example, we are adding a function that outputs a floating-point number. You can replace the respective sections of the previous example, or simply add the code to the prologue and IDL section. The epilogue can be reused completely.
Example 8. Passing a number
%{
#include <stdio.h>
static void
print_double(double x)
{
printf("The number is %f.\n", x);
}
%}
function void js_print_double : print_double (double=1) <static>;
|
The code looks similar to the example above. The only difference is the
extra argument that is passed to the function
print_number. It is of type double and
has a default value of 1.
To test the code, replace the content of tutorial.js by the following lines.
js_print_double(4.5);
js_print_double();
js_print_double("4.5");
|
Again, compile and execute the application.
./tutorial
The number is 4.50000.
The number is 1.00000.
The number is 4.50000.
|
Each line of output corresponds to a call to js_print_double. With the first line, the application simple outputs the supplied number. The generated glue code converts the parameter into a C data type and passes it to the function printf.
The second line is more interesting because here the argument was omitted.
Instead, the glue code automatically used the default value of
1. This feature is very useful for passing save
defaults or setting arguments that are seldom needed explicitly. In the
case that more arguments are supplied than needed, the unnecessary ones
are simply ignored.
The third line again outputs an argument, but here it is passed as a string instead of a number. This demonstrates the ability of automatically handling type conversions within the generated code.
Often it is necessary to return a value from a function call. The necessary glue code can also be generated automatically. To illustrate this, a new function is added to the previous example.
Example 9. Returning a number
%{
#include <stdio.h>
static int
sum(int n, int m)
{
return n+m;
}
static void
print_double(double x)
{
printf("The number is %f.\n", x);
}
%}
function int js_sum : sum (int, int) <static>;
function void js_print_double : print_double (double=1) <static>;
|
The function sum computes the sum of two integers and returns the result back to the JavaScript environment. The necessary glue code is again generated automatically. Notice the int as the return type in the declaration of js_sum.
Replace the content of the file tutorial.js by the following lines
js_print_double(js_sum(1, 2));
js_print_double(js_sum(1, js_sum(2, 3)));
|
and compile and execute the test application.
./tutorial
The number is 3.000000.
The number is 6.000000.
|
At the first line, the JavaScript environment first calls
js_sum with the arguments 1 and
2, and passes the returned sum value to the output
function. The return value is first converted to a JavaScript
representation by js_sum's glue code and given back
to the JavaScript environment. The environment then calls
js_print_double's glue-code function, which is
supplied with the just returned JavaScript value.
The second line's call is similar, but here one of the arguments is again a call to js_sum which is resolved first.
This tutorial only shows some very basic functions of
jsapigen. The rest of this manual will give a
more structured and formal description of the program's facilities. Please
send any remarks or questions to the the project's mailing list at
<jsapigen-devel@lists.sourceforge.net>.
Generating code with jsapigen is divided into two steps. In the first step, the user has to write an interface description that connects the program's C components with its JavaScript engine. jsapigen uses this description in the second step to generate C glue code. The resulting file has to be compiled into the program's binary.
This chapter describes the command jsapigen and its file format.
Invoke jsapigen on the command line by calling
jsapigen [-h] [-V] [-f input] [-o output] [-n namespace] [-s stage] [-t target]
-hDisplays help and exits.
-VDisplays program version and exits.
-f input
Read interface description from file
input. If option
-f is omitted, jsapigen reads from
stdin.
-o output
Write generated C code to file
output. If option
-o is omitted, jsapigen writes to
stdout.
-n namespace
Specifies the namespace of the generated source code. The names of all
generated symbols are prefixed with
namespace. If option
-n is omitted, jsapigen uses
the namespace jj.
-s stage
Makes jsapigen stop at the specified stage. Current
stages are ast, symtabs,
hlcltab, and codegen. If option
-s is omitted, jsapigen
executes all stages.
-t targetSpecifies the target API. Currently jsapigen only supports jsapi.
jsapigen uses a simple, textual file format. Its general layout looks as follows.
%{
/* C implementation code... */
%}
/* Interface description... */
%<
/* C setup code... */
%>
|
The file's content is divided into three sections.
At the beginning of the file there can be some C code. This part is enclosed by %{ and %}. It is intended to be used for implementing native C functions that are used by the JavaScript engine. This part is copied to the output as-is.
At the middle is the interface description. It is translated to C code by jsapigen. The description can contain comments. These are enclosed by /* and */; similar to C comments. Nesting comments is not possible. Comments are stripped by jsapigen and do not appear in the generated glue code. However, comments in the C sections are copied to the output.
At the end of the file there can again be C code. It is enclosed by %< and %>. This is intended for setup and cleanup code, that interacts with the JavaScript engine. It is copied to the output as-is.
This section describes how to write declarations of requests, properties, functions, and classes. jsapigen generates glue code from such declarations, as well as some meta data, which is used to register the generated code with the JavaScript environment.
Requests are calls from C code into the JavaScript environment. Each declared request generates a C function that converts the supplied arguments into their JavaScript counterparts, calls into the JavaScript environment and converts back any returned value.
Request declarations have the following syntax:
request TYPE NATIVE ':' NAME ARGUMENTS ';' |
Request declarations always start with the keyword request.
The request's return type.
The name of the generated C function that implements the request code. This function has the supplied types for its arguments and return value. Additionally, it has a first argument that receives the JavaScript context on which to execute the request.
The request function's name in the JavaScript engine.
A list of types for the arguments to be passed to the JavaScript function. It can be omitted if no arguments are needed. For the arguments, only empty or primitive data types are allowed. Object types are not supported.
Example 1. Defining a request
The scripts loaded for this example have to contain a function 'sum', which returns the sum of its two arguments.
request int sum : sum_request (int, int);
%<
int
main (int argc, char *argv[])
{
JSContext *cx;
int sum;
/* Setup JavaScript environment and context ...
*/
/* Call sum function in JavaScript context cx */
sum = sum_request(cx, 1, 3);
/* Cleanup ...
*/
exit(EXIT_SUCCESS);
}
%>
|
Properties declarations have the following syntax:
property TYPE NAME ':' GETTER ',' SETTER ATTRIBUTES ';' |
Property declarations always start with the keyword property.
The property's type.
The property's name as a member of its parent function.
The property's getter function. It is not possible to read the value of a property if this parameter is omitted.
The property's setter function. Without this parameter, the property's value is declared read-only.
A list of attributes that further specify the property's behavior.
Properties can either be defined in the global context or as methods of classes.
Example 2. Defining the property prop
Without the attribute static the getter and setter functions receive an implicit first parameter that points to the parent object's private data.
%{
struct obj
{
int n;
};
int prop_get(struct obj *this)
{
return this->n;
}
void prop_set(struct obj *this, int n)
{
this->n=n;
}
%}
property int prop : prop_get , prop_set;
|
The general function declaration looks like this:
function TYPE NAME ':' NATIVE ARGUMENTS ATTRIBUTES ';' |
Function declarations always start with the keyword function.
The function's return type.
The function's name in the JavaScript engine.
The name of the native C function, that is called when the function is executed.
A list of arguments to be passed to the native function. This can be omitted if no arguments are needed.
A list of attributes that further specify the function's behavior.
Functions can either be defined in the global context or as methods of classes.
Example 3. Importing the C function c_square as js_square
If the function call parameter is omitted, a default value of 2 is used.
%{
int c_square(int n)
{
return n*n;
}
%}
function int js_square : c_square (int=2) <static>;
|
Function definitions contain a list of types, which are passed to the C function. It is also possible to set a default value for each argument. This value is used if the caller omits the value.
An argument list looks as follows.
'(' TYPE [=VALUE] ',' TYPE [=VALUE] ',' ... ')'
|
The type of an argument.
The argument's default. It is used if the caller does not pass a value
for the argument. If neither a value is passed nor a default value is
given, some internal type-specific default 'default value' is used, e.g
0 for int.
Empty argument lists can be written as (), or (void), or simply be omitted.
By default, C functions take an implicit first argument of type void*. This is a pointer to the parent object's private data. The following example illustrates this.
JavaScript classes are function objects with associated methods, such as other functions or properties.
class NAME
'{'
FUNCTION ';'
PROPERTY ';'
OPERATION ';'
'}' ';'
|
Class declarations always start with the keyword class.
The class' name.
A member function of the class.
A property of the class.
A special operation of the class that is dedicated to a very specific task. This might be a constructor function, which allocates internal resources during an instantiation of the class.
Classes can have operations; such as constructors, finalizers, or similar functions; to handle special purposes.
Constructors are called when a new object is created. A constructor declaration look as follows.
construct ':' NATIVE ARGUMENTS ATTRIBUTES ';' |
Constructor declarations start with the keyword construct.
The native constructor function.
A list of arguments for the native function call.
The constructor function's attributes. Constructor's support the attributes static and suspendable.
Constructor function never receive an implicit first argument. Instead the meaning of the attribute static is modified. If the constructor function is static, its native function is expected to have a return type of void. If the function is non-static, its native function is expected to return void*. This value is the address of the object's private data. It is passed as implicit first argument on each call to a non-static function of the object.
Just before it deallocates an object, the garbage collector calls the object's finalizer function.
finalize ':' NATIVE ATTRIBUTES ';' |
Finalizer declarations start with the keyword finalize.
The native finalizer function.
An attribute list. Finalizers only support the attribute static.
Example 7. Constructors and finalizers
The example shows the use of constructors and finalizers. The constructor allocates memory for the object's private data which is later freed by the finalizer.
%{
#include <stdlib.h>
#include <stdio.h>
struct data
{
int n;
};
static void *
my_class_construct(int n)
{
struct data *This;
This = malloc(sizeof(*This));
if (!This) {
perror("malloc");
return NULL;
}
This->n = n;
return This;
}
static void
my_class_finalize(struct data *This)
{
free(This);
}
%}
class my_class
{
construct : my_class_construct (int);
finalize : my_class_finalize;
};
|
Be aware that an object is not necessarily finalized when it goes out of scope. It is therefore quite likely that the C environment of your program will contain some data that is not referenced from within the JavaScript environment anymore, but appears to be in use.
When a class is called like a function, the JavaScript environment invokes the class' call operator.
call TYPE : NATIVE ARGUMENTS ATTRIBUTES ';' |
Call declarations start with the keyword call.
The native call function.
A list of arguments for the call function.
An attribute list.
The equality operator compares two objects for equality.
equality : NATIVE ARGUMENT ';' |
Equality declarations start with the keyword equality.
The native test function. If the equality test fails, the native function should return 0, or otherwise a non-zero value if it succeeds.
The equality operator always takes one argument which it the type of the comparison's right-hand-side value.
JSAPI provides several types; such as JSNumber, JSString, or JSObject; to the programmer.
IDL types are used to connect JSAPI type to C types. The automatic packing and unpacking of arguments and return values is controlled by their assigned IDL types. Therefore, jsapigen distinguishes among the empty type, primitive types, and object types.
An empty type does never hold any value. There is only one empty type.
Empty types.
The empty type that does not hold any value. It is mapped to the C type void.
A primitive type roughly corresponds to a C type and is converted like-wise. Here is a list of all primitive types.
Primitive types.
A 16-bit integer value. It corresponds to the C type short.
A 32-bit integer value. It corresponds to the C type int.
A 32-bit floating-point value. It corresponds to the C type float.
A 64-bit floating-point value. It corresponds to the C type double.
This is a string value. It is mapped to a C pointer of type const char* which points to a 0-terminated sequence of characters.
This is a wide-string value. It is mapped to a C pointer of type const wchar_t* which points to a 0-terminated sequence of wide characters. The size of wchar_t depends on the C environment.
Any other non-array type name always refers to an object type which has been registered with the JavaScript engine. As the name suggests, these correspond to JavaScript objects.
Example 10. Using an object type.
This example shows the usage of the object type Foo as argument of the function use_foo.
class Foo {
/* This Class Intentionally Left Empty. */
};
function void js_use_foo : use_foo(Foo);
|
An array type corresponds to a C array type. Its elements are converted like the respective primitive or object type. Within the JavaScript environment arrays are always of type Array.
Array types are declared like primitive types with an appended
'[' n ']' . The value of n defines the
length of the array. Within the declaration of function arguments
n can be omitted. The generated code then converts all
elements of the supplied Array object. This allows the passing of
variably-sized arrays to C functions.
Array types.
An array of 16-bit integer values. It corresponds to the C type short*.
An array of 32-bit integer values. It corresponds to the C type int*.
An array of 32-bit floating-point values. It corresponds to the C type float*.
An array of 64-bit floating-point values. It corresponds to the C type double*.
This is an array of string values. It is mapped to a C pointer of type char** which points to an array of pointers to 0-terminated sequences of characters.
This is an array of wide-string values. It is mapped to a C pointer of type wchar_t** which points to an array of pointers to 0-terminated sequences of wide characters.
Any other array-type name always refers to an array of an object type which has been registered with the JavaScript engine.
Example 11. A class declaration containing array types.
This example shows the usage of the array types within class declarations.
%{
static int c_prop[2] = {0, 0};
int* prop_get()
{
return c_prop;
}
void prop_set(int *int_prop)
{
c_prop[0] = int_prop[0];
c_prop[1] = int_prop[1];
}
void c_function(void *this, int *int_array)
{
/* Do something with int_array ... */
return;
}
%}
class Foo {
property double[2] prop : prop_get , prop_set <static>;
function void js_function : c_function (int[]);
};
|
Attributes control the behavior of functions and properties. An attribute list looks as follows.
'<' ATTRIBUTE ',' ATTRIBUTE ',' ... '>' |
This is the name of an attribute that is applied to the function or property.
The following attributes are supported.
The function or property can not be deleted from its parent object. This corresponds to the ECMAscript standard attribute DontDelete.
The function or property is not enumerated. This corresponds to the ECMAscript standard attribute DontEnum.
The function or property is static, so it is added to its parent classes constructor. This attribute also implies that associated C functions, such as native functions or getter/setter functions, do not receive an implicit first argument with the object's private value.
The attribute static very much resembles static behavior in C++ or Java.
In a multi-threaded application, several threads can share the same JavaScript context. However, at any point in time only one request can be executed, while other requests are blocked.
The attribute suspendable marks the current request to be suspended during a call to the native function. This allows one of the waiting requests to become active.
In practice, the attribute suspendable adds a block of JS_SuspendRequest/ JS_ResumeRequest around the native function's call. When using this attribute, make sure you add a pair of JS_BeginRequest/ JS_EndRequest around each call of JS_CallFunctions. To enable suspendable calls, define the preprocessor macro JS_THREADSAFE during compilation.
The attribute value marks a property's getter and setter functions to be names of variables or constants, instead of functions. This saves oneself of the implementation of very simple getter or setter functions, which only return or assign a value.
Declaring properties without setter method but with the value attribute, provides a convenient way of adding constants to a class.
For each class, jsapigen generates arrays with the classes properties and functions. Additionally, jsapigen generates a class description of type JSClass. These information are meant to be passed to JS_InitClass.
NAME_static_ps[]
Contains property specs for all static properties of a class. Replace
NAME with the classes name.
NAME_ps[]
Contains property specs for all non-static properties of a class. Replace
NAME with the classes name.
Contains property specs for all properties of the global object.
NAME_static_fs[]
Contains function specs for all static functions of a class. Replace
NAME with the classes name.
NAME_fs[]
Contains function specs for all non-static functions of a class. Replace
NAME with the classes name.
Contains function specs for all functions of the global object.
A class description.
For convenience, an initialization function is provided for each class. The function receives the JavaScript context and the parent object. It returns the prototype for the newly registered class or NULL on error.
static JSObject* jjNAME_init(JSContext *cx, JSObject *parent); |
Example 12. Registering a class
This example shows how to register a generated class with properties and functions. The user only has to implement and call the function register_everything, which does all the work.
%{
#include <stdio.h>
static void
global_func(const char *s)
{
printf("%s", s);
}
static void
my_class_func(int n)
{
printf("%d\n", n);
}
static double my_class_prop = 0.0;
%}
function void global_func : global_func(cstring) <static>;
class my_class
{
function void func : my_class_func(int) <static>;
property double prop: my_class_prop , my_class_prop <value>;
};
%<
JSBool
register_everything(JSContext *cx, JSObject *global)
{
/* Register my_class */
if (!jjmy_class_init(cx, global)) {
return JS_FALSE;
}
/* Add global properties and functions */
if (JS_DefineProperties(cx, global, jj_ps) != JS_TRUE) {
return JS_FALSE;
}
if (JS_DefineFunctions(cx, global, jj_fs) != JS_TRUE) {
return JS_FALSE;
}
return JS_TRUE;
}
%>
|
When passing arguments from JavaScript to C functions, the glue code occasionally has to allocate memory. This is typically done by taking memory from the program's heap, but jsapigen also allows the allocation of stack memory.
Heap allocation can impose a serious overhead on the program's performance. The code allocates memory by calling malloc, which might involve a costly search of a free memory area and a call to the operating system. At the end of the glue code, the memory is released via a call to free, which includes the modification of internal data structures.
To minimize the overhead, jsapigen allows the creation of glue code that allocates memory on the stack. Allocating memory on the stack has the advantage that no costly searches have to be done. Only the thread's stack pointer is changed. Stack allocation is done by the function alloca. If your platform supports alloca, define the preprocessor macros HAVE_ALLOCA_H and HAVE_ALLOCA while compiling the generated glue code. The macro HAVE_ALLOCA_H makes the code include the file alloca.h, and HAVE_ALLOCA enables the use of alloca.
Stack-based allocation has the danger of overflowing the maximum stack
size if the allocated memory block is too large. To prevent this from
happening, the maximum size for stack allocation has to be set explicitly.
Each generated file with glue code contains the static variable
jj_alloca_limit, which holds this value. Its initial
value is zero, so stack allocation is disabled by default.
Example 1. Enabling stack-based allocation
The following example sets the maximum size for stack-based allocation to 64 byte. Any memory block smaller than this value will be allocated on the stack, any memory block equal or larger will be allocated on the heap.
%{
/* Prologue */
%}
/* Interface declarations */
%<
int
register(JSContext *cx, JSObject *global)
{
/* Set stack-allocation limit to 64 bytes */
jj_alloca_limit = 64;
/* Register generated glue code... */
return 0;
}
%>
|
This section contains various tips and lessons which have proven helpful
during the development of applications with
jsapigen. Please send any tips that should be
listed here to <jsapigen-devel@lists.sourceforge.net>.
Don't write constructors like the following.
struct c_object
{
int some_element;
};
struct c_object * c_object_construct(void)
{
struct c_object *this = malloc(sizeof(*this));
assert(this);
this->some_element = 0;
return this;
}
|
This is not only bad practice because the contruct function actually does more than one thing, but also prevents the initialization function to be reused in other contexts. Its better to write the construction like this.
struct c_object
{
int some_element;
};
void c_object_init(struct c_object *this)
{
assert(this);
this->some_element = 0;
}
struct c_object * c_object_construct(void)
{
struct c_object *this = malloc(sizeof(*this));
assert(this);
c_object_init(this);
return this;
}
|
Note that the use of malloc might be dangerous here. See below for more information.
SpiderMonkey requires private data of objects to be located at even memory addresses. The following constructor is therefore dangerous.
struct c_object * c_object_construct(void)
{
struct c_object *this = malloc(sizeof(*this));
assert(this);
c_object_init(this);
return this;
}
|
A better solution is to allocate memory with the function posix_memalign. This will guarantee that any allocated memory will be correctly aligned.
struct c_object * c_object_construct(void)
{
struct c_object *this = NULL;
int err = posix_memalign(&this, sizeof(void*), sizeof(*this));
assert(!err);
c_object_init(this);
return this;
}
|
Alignment is controlled by the second argument of this function. Its value
should be the smallest value that is a multiple of the alignment of your
C-object's type, a multiple of sizeof(void*) and a power
of two at the same time.
If you allocate memory in a constructor you should free this memory in the finalizer. In fact, finalizers should be written as the inverse of the constructor.
struct c_object * c_object_construct(void)
{
struct c_object *this = NULL;
int err = posix_memalign(&this, sizeof(void*), sizeof(*this));
assert(!err);
c_object_init(this);
return this;
}
void c_object_finalize(struct c_object *this)
{
c_object_uninit(this);
free(this);
}
|
This code assures that any memory allocated during the construction is free'd when the object is finalized. Finalization might not necessarily occur when the JavaScript object goes out of scope, but at any later point in time when the garbage collector decides to free the object.
By now, jsapigen has several limitations. Some of these are listed below.
Prototypes are not suported yet.
More types might be necessary to better reflect the C types.
Not all details of the JSAPI are supported. However, most are obscure special operators which are seldomly needed.
Integrating jsapigen in a Makefile is very simple. Add a rule for building the glue code and integrate that rule into the build process.
Example 2. Makefile integration
This is an example of a Makefile for the tutorial's build process. It compiles tutorial.j into the binary tutorial. The application's glue code is thereby generated automatically.
tutorial : tutorial.o
gcc -o tutorial -lmozjs tutorial.o
tutorial.o : tutorial.j.c
gcc -c -o tutorial.o -DXP_UNIX -I/usr/include/mozjs -g3 tutorial.j.c
tutorial.j.c :
jsapigen < tutorial.j > tutorial.j.c
.PHONY : clean
clean :
rm -fr tutorial
rm -fr *.o
rm -fr *.j.c
|
Many Free Software projects use GNU Automake and GNU Autoconf as their build system. Along with this manual or the source release the Autoconf macro ACX_PROG_JSAPIGEN is provided. It searches the system for jsapigen and provides it to Automake.
Example 3. GNU Autotools integration
Call the macro ACX_PROG_JSAPIGEN from within the
file configure.ac and copy the following lines to
Makefile.am in the source-code directory. Any files
in the variable SOURCES that end with
.j will now automatically handled by
jsapigen.
.j.o:
$(JSAPIGEN) $(JFLAGS) -f $< -o $<.c
$(COMPILE) -c -o $@ $<.c
mostlyclean-local:
rm -f *.j.c
|
dnl @synopsis ACX_PROG_JSAPIGEN ([argument])
dnl @summary The syntax how to use the macro.
dnl
dnl A description of what the macro does and what results
dnl it produces.
dnl
dnl This description may extend over multiple paragraphs,
dnl if you like.
dnl
dnl Every line that is indented by more than one
dnl blank will be formatted verbatim, so that you
dnl can include examples in the description.
dnl
dnl @version 2008-06-03
dnl @author Thomas Zimmermann <tdz@users.sourceforge.net>
dnl @license GPLWithACException
dnl
AC_DEFUN([ACX_PROG_JSAPIGEN],
[AC_PATH_PROGS([JSAPIGEN], [jsapigen])
AC_ARG_VAR([JSAPIGEN],
[The name of the `JavaScript API Generator' to use. Defaults to `jsapigen'.])
AC_ARG_VAR([JFLAGS],
[The list of default arguments for $JSAPIGEN. Empty by default.])
])
|
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or convey a specific copy of the covered work, then the patent license
you grant is automatically extended to all recipients of the covered
work and works based on it.
A patent license is "discriminatory" if it does not include within
the scope of its coverage, prohibits the exercise of, or is
conditioned on the non-exercise of one or more of the rights that are
specifically granted under this License. You may not convey a covered
work if you are a party to an arrangement with a third party that is
in the business of distributing software, under which you make payment
to the third party based on the extent of your activity of conveying
the work, and under which the third party grants, to any of the
parties who would receive the covered work from you, a discriminatory
patent license (a) in connection with copies of the covered work
conveyed by you (or copies made from those copies), or (b) primarily
for and in connection with specific products or compilations that
contain the covered work, unless you entered into that arrangement,
or that patent license was granted, prior to 28 March 2007.
Nothing in this License shall be construed as excluding or limiting
any implied license or other defenses to infringement that may
otherwise be available to you under applicable patent law.
12. No Surrender of Others' Freedom.
If conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License. If you cannot convey a
covered work so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you may
not convey it at all. For example, if you agree to terms that obligate you
to collect a royalty for further conveying from those to whom you convey
the Program, the only way you could satisfy both those terms and this
License would be to refrain entirely from conveying the Program.
13. Use with the GNU Affero General Public License.
Notwithstanding any other provision of this License, you have
permission to link or combine any covered work with a work licensed
under version 3 of the GNU Affero General Public License into a single
combined work, and to convey the resulting work. The terms of this
License will continue to apply to the part which is the covered work,
but the special requirements of the GNU Affero General Public License,
section 13, concerning interaction through a network will apply to the
combination as such.
14. Revised Versions of this License.
The Free Software Foundation may publish revised and/or new versions of
the GNU General Public License from time to time. Such new versions will
be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.
Each version is given a distinguishing version number. If the
Program specifies that a certain numbered version of the GNU General
Public License "or any later version" applies to it, you have the
option of following the terms and conditions either of that numbered
version or of any later version published by the Free Software
Foundation. If the Program does not specify a version number of the
GNU General Public License, you may choose any version ever published
by the Free Software Foundation.
If the Program specifies that a proxy can decide which future
versions of the GNU General Public License can be used, that proxy's
public statement of acceptance of a version permanently authorizes you
to choose that version for the Program.
Later license versions may give you additional or different
permissions. However, no additional obligations are imposed on any
author or copyright holder as a result of your choosing to follow a
later version.
15. Disclaimer of Warranty.
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
16. Limitation of Liability.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES.
17. Interpretation of Sections 15 and 16.
If the disclaimer of warranty and limitation of liability provided
above cannot be given local legal effect according to their terms,
reviewing courts shall apply local law that most closely approximates
an absolute waiver of all civil liability in connection with the
Program, unless a warranty or assumption of liability accompanies a
copy of the Program in return for a fee.
END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.
<one line to give the program's name and a brief idea of what it does.>
Copyright (C) <year> <name of author>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
Also add information on how to contact you by electronic and paper mail.
If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:
<program> Copyright (C) <year> <name of author>
This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the appropriate
parts of the General Public License. Of course, your program's commands
might be different; for a GUI interface, you would use an "about box".
You should also get your employer (if you work as a programmer) or school,
if any, to sign a "copyright disclaimer" for the program, if necessary.
For more information on this, and how to apply and follow the GNU GPL, see
<http://www.gnu.org/licenses/>.
The GNU General Public License does not permit incorporating your program
into proprietary programs. If your program is a subroutine library, you
may consider it more useful to permit linking proprietary applications with
the library. If this is what you want to do, use the GNU Lesser General
Public License instead of this License. But first, please read
<http://www.gnu.org/philosophy/why-not-lgpl.html>.
|
GNU Free Documentation License
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or noncommercially.
Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible
for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense. It
complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does. But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book. We recommend this License
principally for works whose purpose is instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be
distributed under the terms of this License. Such a notice grants a
world-wide, royalty-free license, unlimited in duration, to use that
work under the conditions stated herein. The "Document", below,
refers to any such manual or work. Any member of the public is a
licensee, and is addressed as "you". You accept the license if you
copy, modify or distribute the work in a way requiring permission
under copyright law.
A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section of
the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall subject
(or to related matters) and contains nothing that could fall directly
within that overall subject. (Thus, if the Document is in part a
textbook of mathematics, a Secondary Section may not explain any
mathematics.) The relationship could be a matter of historical
connection with the subject or with related matters, or of legal,
commercial, philosophical, ethical or political position regarding
them.
The "Invariant Sections" are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
that says that the Document is released under this License. If a
section does not fit the above definition of Secondary then it is not
allowed to be designated as Invariant. The Document may contain zero
Invariant Sections. If the Document does not identify any Invariant
Sections then there are none.
The "Cover Texts" are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
the Document is released under this License. A Front-Cover Text may
be at most 5 words, and a Back-Cover Text may be at most 25 words.
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images composed of
pixels) generic paint programs or (for drawings) some widely available
drawing editor, and that is suitable for input to text formatters or
for automatic translation to a variety of formats suitable for input
to text formatters. A copy made in an otherwise Transparent file
format whose markup, or absence of markup, has been arranged to thwart
or discourage subsequent modification by readers is not Transparent.
An image format is not Transparent if used for any substantial amount
of text. A copy that is not "Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format, SGML
or XML using a publicly available DTD, and standard-conforming simple
HTML, PostScript or PDF designed for human modification. Examples of
transparent image formats include PNG, XCF and JPG. Opaque formats
include proprietary formats that can be read and edited only by
proprietary word processors, SGML or XML for which the DTD and/or
processing tools are not generally available, and the
machine-generated HTML, PostScript or PDF produced by some word
processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page. For works in
formats which do not have any title page as such, "Title Page" means
the text near the most prominent appearance of the work's title,
preceding the beginning of the body of the text.
A section "Entitled XYZ" means a named subunit of the Document whose
title either is precisely XYZ or contains XYZ in parentheses following
text that translates XYZ in another language. (Here XYZ stands for a
specific section name mentioned below, such as "Acknowledgements",
"Dedications", "Endorsements", or "History".) To "Preserve the Title"
of such a section when you modify the Document means that it remains a
section "Entitled XYZ" according to this definition.
The Document may include Warranty Disclaimers next to the notice which
states that this License applies to the Document. These Warranty
Disclaimers are considered to be included by reference in this
License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and has
no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no other
conditions whatsoever to those of this License. You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute. However, you may accept
compensation in exchange for copies. If you distribute a large enough
number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and
you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have
printed covers) of the Document, numbering more than 100, and the
Document's license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover. Both covers must also clearly and legibly identify
you as the publisher of these copies. The front cover must present
the full title with all words of the title equally prominent and
visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve
the title of the Document and satisfy these conditions, can be treated
as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.
If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material.
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.
It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it. In addition, you must do these things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document). You may use the same title as a previous version
if the original publisher of that version gives permission.
B. List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has fewer than five),
unless they release you from this requirement.
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.
G. Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page. If
there is no section Entitled "History" in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.
J. Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on. These may be placed in the "History" section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the section all
the substance and tone of each of the contributor acknowledgements
and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section titles.
M. Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled "Endorsements"
or to conflict in title with any Invariant Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant. To do this, add their titles to the
list of Invariant Sections in the Modified Version's license notice.
These titles must be distinct from any other section titles.
You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.
You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version. Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity. If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled "History"
in the various original documents, forming one section Entitled
"History"; likewise combine any sections Entitled "Acknowledgements",
and any sections Entitled "Dedications". You must delete all sections
Entitled "Endorsements".
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document's Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole
aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers. In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except
as expressly provided for under this License. Any other attempt to
copy, modify, sublicense or distribute the Document is void, and will
automatically terminate your rights under this License. However,
parties who have received copies, or rights, from you under this
License will not have their licenses terminated so long as such
parties remain in full compliance.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License "or any later version" applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation. If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation.
ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:
Copyright (c) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled "GNU
Free Documentation License".
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.
|