擴展Ruby

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在Ruby中擴展Ruby的新功能是很容易的，如果你用c來寫底層的代碼，那么我們就能更好的擴展Ruby的功能。

用c來擴展ruby是非常簡單的事情。比如，我們我們在為Sunset Diner and Grill建造一個基于internet的自動點唱機，它將從硬盤播放mp3文件或者從cd唱機播放cd音頻。我們想從ruby程序中控制硬件系統(tǒng)，硬件提供商為我們提供了一個C語言的頭文件，和一個二進制的實現(xiàn)庫文件，我們所需要做的是創(chuàng)建一個Ruby對象，映射到相應(yīng)的C函數(shù)調(diào)用。

在進一步使Ruby和C語言一起工作之前，先讓我們從c語言角度看看ruby對象是什么樣的。[本章又很多信息都是從隨同ruby發(fā)布的 README.EXT摘錄的，如果你想擴展ruby的話，可以參考最新版本的README.EXT]

C語言中的Ruby對象

我們要看的第一件事情是在C語言中如何表示和訪問Ruby的數(shù)據(jù)類型。Ruby中所有東西都是對象，所有的變量都指向一個對象。在C語言中，所有Ruby變量的類型都是VALUE，它要們是一個指向Ruby對象的指針，要們指向一個立即值（immediate value），比如Fixnum。

這也是Ruby如何在C中實現(xiàn)面向?qū)ο蟮拇a的：一個Ruby對象是在內(nèi)存中分配的一個結(jié)構(gòu)，這個結(jié)構(gòu)包括一個包括實例變量的表，和關(guān)于關(guān)于類的信息。這個類本身是另一個對象（分配了內(nèi)存結(jié)構(gòu)），有一個包括類中方法定義的表。

VALUE 是一個指針

VALUE 是一個指針指向一個定義好的Ruby對象結(jié)構(gòu)，而不能指向其他類型的結(jié)構(gòu)。每個Ruby內(nèi)建的類的結(jié)構(gòu)定義在"ruby.h"中，命名都以R開頭加類名，比如RString和RArray。

有幾種辦法來判斷一個VALUE所對應(yīng)的結(jié)構(gòu)的類型。宏TYPE( obj )可以返回代表指定對象的C類型的常量的值：T_OBJECT, T_STRING或其它。代表內(nèi)建類的常量在ruby.h中定義。注意這里我們說得類型是實現(xiàn)上的細節(jié)，而不是向某一個對象的類。(Note that the type we are referring to here is an implementation detail---it is not the same as the class of an object.)

?如果你想確認一個vaulue指針指向一個特定的結(jié)構(gòu)，你可以用宏Check_Type。如果給定的value不是type型的，將會產(chǎn)生一個TypeError 的異常。（type是T_STRING, T_FLOAT或其它）。

Check_Type(VALUE value, int type)

如果你很關(guān)心速度，這里有一些很快的宏來判斷立即值Fixnum 和nil：
FIXNUM_P(value) -> non-zero if value is a Fixnum
NIL_P(value)??? -> non-zero if value is nil
RTEST(value)??? -> non-zero if value is neither nil nor false

Again, note that we are talking about ``type'' as the C structure that represents a particular built-in type. The class of an object is a different beast entirely. The class objects for the built-in classes are stored in C global variables named rb_c Classname (for instance, rb_cObject); modules are named rb_m Modulename.

It wouldn't be advisable to mess with the data in these structures directly, however---you may look, but don't touch unless you are fond of debuggers. You should normally use only the supplied C functions to manipulate Ruby data (we'll talk more about this in just a moment).

However, in the interests of efficiency you may need to dig into these structures to obtain data. In order to dereference members of these C structures, you have to cast the generic VALUE to the proper structure type. ruby.h contains a number of macros that perform the proper casting for you, allowing you to dereference structure members easily. These macros are named RCLASSNAME , as in RSTRING or RARRAY. For example:

VALUE str, arr;
RSTRING(str)->len -> length of the Ruby string
RSTRING(str)->ptr -> pointer to string storage
RARRAY(arr)->len  -> length of the Ruby array
RARRAY(arr)->capa -> capacity of the Ruby array
RARRAY(arr)->ptr  -> pointer to array storage

VALUE 作為立即對象（Immediate Object）

我們上面說過，立即值不是指針：: Fixnum, Symbol, true, false, 和 nil 直接存儲在 VALUE中。

Fixnum 值在存儲器中占用31個bit(其他的cpu結(jié)構(gòu)可能占用63個bit)，然后這個值左移一位，最后一位設(shè)置為 "1"，當(dāng)VAULE指向其他類型的數(shù)據(jù)時，這個最低位（LSB）總是"0"，其他的立即值得LSB也是0，這樣，可以通過這個位的值是0還是1來判斷這個值是不是Fixnum。

其它的立即值true, false, nil在C語言中用常量Qtrue, Qfalse, Qnil來表示，你可以用這些常量來測試一個值是不是true，false，nil等，或者用轉(zhuǎn)換宏來測試。

Writing Ruby in C

用Ruby編程的樂趣之一是你可以在C語言里像Ruby中一樣實現(xiàn)，你可以用同樣的方法名，同樣的邏輯，除了一些語法的區(qū)別，比如，這里有一個用Ruby寫的簡單的test類：

class?Test ??def?initialize ????@arr?=?Array.new ??end ??def?add(anObject) ????@arr.push(anObject) ??end end

完成上面同樣功能的C代碼如下：

#include?"ruby.h" static?VALUE?t_init(VALUE?self) { ??VALUE?arr; ??arr?=?rb_ary_new(); ??rb_iv_set(self,?"@arr",?arr); ??return?self; } static?VALUE?t_add(VALUE?self,?VALUE?anObject) { ??VALUE?arr; ??arr?=?rb_iv_get(self,?"@arr"); ??rb_ary_push(arr,?anObject); ??return?arr; } VALUE?cTest; void?Init_Test()?{ ??cTest?=?rb_define_class("Test",?rb_cObject); ??rb_define_method(cTest,?"initialize",?t_init,?0); ??rb_define_method(cTest,?"add",?t_add,?1); }

讓我們詳細的看看這里面的細節(jié)，這段程序包括了本章的很多重要的內(nèi)容。首先，我們需要把ruby.h文件引入，才能使用其中的一些預(yù)定義的東西。

然后來看看最后一個函數(shù)：Init_Test。每個類或模塊都要定義一個C的全局函數(shù) Init_name局函，這個函數(shù)將會在ruby解釋器第一次載入擴展name的時候執(zhí)行，它用來初始化這個擴展（extension ），使它融入Ruby的環(huán)境中。這個例子里，我們定義了一個類Test，它是Object的子類。（Object在ruby.h中用rb_cObject表示）

然后我們建立了兩個函數(shù)add和initialize，這兩個都是類Test的實例方法。函數(shù)rb_define_method 綁定了Ruby中的方法和對應(yīng)的C語言的實現(xiàn)。所以，在Ruby中調(diào)用這個類的add方法，將會調(diào)用C函數(shù)t_add。

類似的，當(dāng)在Ruby中調(diào)用Test的new方法時，將會調(diào)用initialize方法，也就是C程序里面的t_init方法（沒有Ruby參數(shù)）。

?現(xiàn)在回來看看方法initialize的定義，我們說過它不需要參數(shù)，但是那里卻真的有一個參數(shù)。除了ruby方法中的參數(shù)，每個方法都會被傳遞一個最初的VALUE參數(shù)，這個VALUE指的是方法的接收者（receiver ），類似Ruby中的self。

在initialize 方法中我們做的是創(chuàng)建一個Ruby中的數(shù)組，并用實例變量@arr指向這個數(shù)組。 Just as you would expect if you were writing Ruby source, referencing an instance variable that doesn't exist creates it.

最后，t_add方法從當(dāng)前對象取得實例變量@arr，并用 Array#push 把傳遞過來的參數(shù)放到里面。當(dāng)用這種方法訪問實例變量的時候，前綴@是必不可少的，否則在Ruby中將不能訪問這個變量。

Despite the extra, clunky syntax that C imposes, you're still writing in Ruby---you can manipulate objects using all of the method calls you've come to know and love, with the added advantage of being able to craft tight, fast code when needed.

警告: 從Ruby中能訪問的C語言中的所有方法都必須返回一個VALUE值，即使Qnil也行。否則會出現(xiàn)core dump。

要想在Ruby中使用上面的C代碼，只需要動態(tài)的把它require進來就行。

require?"code/ext/Test" t?=?Test.new t.add("Bill?Chase")

C/Ruby 類型轉(zhuǎn)換函數(shù)和宏 從C 類型轉(zhuǎn)換到 Ruby： INT2NUM(int) -> Fixnum or Bignum INT2FIX(int) -> Fixnum (faster) INT2NUM(long or int) -> Fixnum or Bignum INT2FIX(long or int) -> Fixnum (faster) CHR2FIX(char) -> Fixnum rb_str_new2(char *) -> String rb_float_new(double) -> Float 從Ruby對象轉(zhuǎn)換到C的數(shù)據(jù)類型： int NUM2INT(Numeric) (Includes type check) int FIX2INT(Fixnum) (Faster) unsigned int NUM2UINT(Numeric) (Includes type check) unsigned int FIX2UINT(Fixnum) (Includes type check) long NUM2LONG(Numeric) (Includes type check) long FIX2LONG(Fixnum) (Faster) unsigned long NUM2ULONG(Numeric) (Includes type check) char NUM2CHR(Numeric or String) (Includes type check) char * STR2CSTR(String) char * rb_str2cstr(String, int *length) Returns length as well double NUM2DBL(Numeric)

在C語言中運行Ruby表達式

如果你在C語言中編程，而且需要用到一些Ruby的表達式，但是不想寫一段代碼來實現(xiàn)，你可以用C版本的eval。假如你有一個數(shù)組，需要把里面的flag標(biāo)志都清除：

rb_eval_string("anObject.each{|x|?x.clearFlag?}");

如果你只是想調(diào)用一個特別的方法，可以這樣：

If you just want to call a particular method (which is cheaper than eval-ing an entire string) you can use

rb_funcall(receiver,?method_id,?argc,?...)

在Ruby 和 C之間共享數(shù)據(jù)

我們已經(jīng)涉及到了很多基礎(chǔ)的東西，現(xiàn)在來看看我們自動點唱機的例子，我們要用Ruby包裝C代碼，還要在兩種語言之間共享數(shù)據(jù)。

直接共享變量

盡管你可以在C中和Ruby中各維護一個變量，并保持它們之間的同步，但是這樣做是不可取得，違反了DRY（Don't Repeat Yourself）原則。更好的方法是直接在Ruby和C之間共享一個變量，你可以通過在C語言里面創(chuàng)建一個Ruby對象，然后把它綁定到一個Ruby中地全局變量來共享一個全局變量，在這種情況下，"$"是可選的，但是為了閱讀方便最好還是在前面加上"$"。

VALUE?hardware_list; hardware_list?=?rb_ary_new(); rb_define_variable("$hardware",?&hardware_list); ... rb_ary_push(hardware_list,?rb_str_new2("DVD")); rb_ary_push(hardware_list,?rb_str_new2("CDPlayer1")); rb_ary_push(hardware_list,?rb_str_new2("CDPlayer2"));

然后，在Ruby中就可以$hardware來訪問C語言中的變量hardware_list。

$hardware

?

["DVD",?"CDPlayer1",?"CDPlayer2"]

You can also create hooked variables that will call a specified function when the variable is accessed, and virtual variables that only call the hooks---no actual variable is involved. See the API section that begins on page 189 for details.

If you create a Ruby object from C and store it in a C global variable without exporting it to Ruby, you must at least tell the garbage collector about it, lest ye be reaped inadvertently:

VALUE?obj; obj?=?rb_ary_new(); rb_global_variable(obj);

包裝C結(jié)構(gòu)（Wrapping C Structures）

Now on to the really fun stuff. We've got the vendor's library that controls the audio CD jukebox units, and we're ready to wire it into Ruby. The vendor's header file looks like this:

typedef?struct?_cdjb?{ ??int?statusf; ??int?request; ??void?*data; ??char?pending; ??int?unit_id; ??void?*stats; }?CDJukebox; //?Allocate?a?new?CDPlayer?structure?and?bring?it?online CDJukebox?*CDPlayerNew(int?unit_id); //?Deallocate?when?done?(and?take?offline) void?CDPlayerDispose(CDJukebox?*rec); //?Seek?to?a?disc,?track?and?notify?progress void?CDPlayerSeek(CDJukebox?*rec, ??????????????????int?disc, ??????????????????int?track, ??????????????????void?(*done)(CDJukebox?*rec,?int?percent)); //?...?others... //?Report?a?statistic double?CDPlayerAvgSeekTime(CDJukebox?*rec);

This vendor has its act together; while the vendor might not admit it, the code is written with an object-oriented flavor. We don't know what all those fields mean within the CDJukeBox structure, but that's okay---we can treat it as an opaque pile of bits. The vendor's code knows what to do with it, we just have to carry it around.

Anytime you have a C-only structure that you would like to handle as a Ruby object, you should wrap it in a special, internal Ruby class called DATA (type T_DATA). There are two macros to do this wrapping, and one to retrieve your structure back out again.

C Datatype Wrapping
VALUE?	Data_Wrap_Struct(VALUE?class, void?(*mark)(), void?(*free)(), void?*ptr")
?	Wraps the given C datatype ptr, registers the two garbage collection routines (see below), and returns a VALUE pointer to a genuine Ruby object. The C type of the resulting object is T_DATA and its Ruby class is class.
VALUE?	Data_Make_Struct(VALUE?class, c-type, void?(*mark)(), void?(*free)(), c-type *")
?	Allocates a structure of the indicated type first, then proceeds as Data_Wrap_Struct. c-type is the name of the C datatype that you're wrapping, not a variable of that type.
?	Data_Get_Struct(VALUE?obj,c-type,c-type *")
?	Returns the original pointer. This macro is a type-safe wrapper around the macro DATA_PTR(obj), which evaluates the pointer.

The object created by Data_Wrap_Struct is a normal Ruby object, except that it has an additional C datatype that can't be accessed from Ruby. As you can see in Figure 17.1 on page 177, this C datatype is separate from any instance variables that the object contains. But since it's a separate thing, how do you get rid of it when the garbage collector claims this object? What if you have to release some resource (close some file, clean up some lock or IPC mechanism, and so on)?

Figure not available...

In order to participate in Ruby's mark-and-sweep garbage collection process, you need to define a routine to free your structure, and possibly a routine to mark any references from your structure to other structures. Both routines take a void pointer, a reference to your structure. The mark routine will be called by the garbage collector during its ``mark'' phase. If your structure references other Ruby objects, then your mark function needs to identify these objects using rb_gc_mark(value). If the structure doesn't reference other Ruby objects, you can simply pass 0 as a function pointer.

When the object needs to be disposed of, the garbage collector will call the free routine to free it. If you have allocated any memory yourself (for instance, by using Data_Make_Struct), you'll need to pass a free function---even if it's just the standard C library's free routine. For complex structures that you have allocated, your free function may need to traverse the structure to free all the allocated memory.

First a simple example, without any special handling. Given the structure definition

typedef?struct?mp3info?{ ??char?*title; ??char?*artist; ??int??genre; }?MP3Info;

we can create a structure, populate it, and wrap it as an object.[We cheat a bit in this example. Our MP3Info structure has a couple of char pointers in it. In our code we initialize them from two static strings. This means that we don't have to free these strings when the MP3Info structure is freed. If we'd allocated these strings dynamically, we'd have to write a free method to dispose of them.]

MP3Info?*p; VALUE?info; p?=?ALLOC(MP3Info); p->artist?=?"Maynard?Ferguson"; p->title?=?"Chameleon"; ... info?=?Data_Wrap_Struct(cTest,?0,?free,?p);

info is a VALUE type, a genuine Ruby object of class Test (represented in C by the built-in type T_DATA). You can push it onto an array, hold a reference to it in an object, and so on. At some later point in the code, we may want to access this structure again, given the VALUE:

VALUE doit(VALUE info) { MP3Info *p; Data_Get_Struct(info, MP3Info, p); ... p->artist -> "Maynard Ferguson" p->title -> "Chameleon" ... }

In order to follow convention, however, you may need a few more things: support for an initialize method, and a ``C-constructor.'' If you were writing Ruby source, you'd allocate and initialize an object by calling new. In C extensions, the corresponding call is Data_Make_Struct. However, although this allocates memory for the object, it does not automatically call an initialize method; you need to do that yourself:

info?=?Data_Make_Struct(cTest,?MP3Info,?0,?free,?one); rb_obj_call_init(info,?argc,?argv);

This has the benefit of allowing subclasses in Ruby to override or augment the basic initialize in your class. Within initialize, it is allowable (but not necessarily advisable) to alter the existing data pointer, which may be accessed directly with DATA_PTR(obj).

And finally, you may want to define a ``C-constructor''---that is, a globally available C function that will create the object in one convenient call. You can use this function within your own code or allow other extension libraries to use it. All of the built-in classes support this idea with functions such as rb_str_new, rb_ary_new, and so on. We can make our own:

VALUE?mp3_info_new()?{ ??VALUE?info; ??MP3Info?*one; ??info?=?Data_Make_Struct(cTest,?MP3Info,?0,?free,?one); ??... ??rb_obj_call_init(info,?0,?0); ??return?info; }

An Example

Okay, now we're ready for a full-size example. Given our vendor's header file above, we write the following code.

#include?"ruby.h" #include?"cdjukebox.h" VALUE?cCDPlayer; static?void?cd_free(void?*p)?{ ??CDPlayerDispose(p); } static?void?progress(CDJukebox?*rec,?int?percent) { ??if?(rb_block_given_p())?{ ????if?(percent?>?100)?percent?=?100; ????if?(percent?<?0)?percent?=?0; ????rb_yield(INT2FIX(percent)); ??} } static?VALUE cd_seek(VALUE?self,?VALUE?disc,?VALUE?track) { ??CDJukebox?*ptr; ??Data_Get_Struct(self,?CDJukebox,?ptr); ??CDPlayerSeek(ptr, ???????????????NUM2INT(disc), ???????????????NUM2INT(track), ???????????????progress); ??return?Qnil; } static?VALUE cd_seekTime(VALUE?self) { ??double?tm; ??CDJukebox?*ptr; ??Data_Get_Struct(self,?CDJukebox,?ptr); ??tm?=?CDPlayerAvgSeekTime(ptr); ??return?rb_float_new(tm); } static?VALUE cd_unit(VALUE?self) { ??return?rb_iv_get(self,?"@unit"); } static?VALUE cd_init(VALUE?self,?VALUE?unit) { ??rb_iv_set(self,?"@unit",?unit); ??return?self; } VALUE?cd_new(VALUE?class,?VALUE?unit) { ??VALUE?argv[1]; ??CDJukebox?*ptr?=?CDPlayerNew(NUM2INT(unit)); ??VALUE?tdata?=?Data_Wrap_Struct(class,?0,?cd_free,?ptr); ??argv[0]?=?unit; ??rb_obj_call_init(tdata,?1,?argv); ??return?tdata; } void?Init_CDJukebox()?{ ??cCDPlayer?=?rb_define_class("CDPlayer",?rb_cObject); ??rb_define_singleton_method(cCDPlayer,?"new",?cd_new,?1); ??rb_define_method(cCDPlayer,?"initialize",?cd_init,?1); ??rb_define_method(cCDPlayer,?"seek",?cd_seek,?2); ??rb_define_method(cCDPlayer,?"seekTime",?cd_seekTime,?0); ??rb_define_method(cCDPlayer,?"unit",?cd_unit,?0); }

Now we have the ability to control our jukebox from Ruby in a nice, object-oriented manner:

require?"code/ext/CDJukebox" p?=?CDPlayer.new(1) puts?"Unit?is?#{p.unit}" p.seek(3,?16)?{|x|?puts?"#{x}%?done"?} puts?"Avg.?time?was?#{p.seekTime}?seconds"

produces:

Unit?is?1 26%?done 79%?done 100%?done Avg.?time?was?1.2?seconds

This example demonstrates most of what we've talked about so far, with one additional neat feature. The vendor's library provided a callback routine---a function pointer that is called every so often while the hardware is grinding its way to the next disc. We've set that up here to run a code block passed as an argument to seek. In the progress function, we check to see if there is an iterator in the current context and, if there is, run it with the current percent done as an argument.

Memory Allocation

You may sometimes need to allocate memory in an extension that won't be used for object storage---perhaps you've got a giant bitmap for a Bloom filter, or an image, or a whole bunch of little structures that Ruby doesn't use directly.

In order to work correctly with the garbage collector, you should use the following memory allocation routines. These routines do a little bit more work than the standard malloc. For instance, if ALLOC_N determines that it cannot allocate the desired amount of memory, it will invoke the garbage collector to try to reclaim some space. It will raise a NoMemError if it can't or if the requested amount of memory is invalid.

Memory Allocation
type *?	ALLOC_N(c-type, n")
?	Allocates n c-type objects, where c-type is the literal name of the C type, not a variable of that type.
type *?	ALLOC(c-type")
?	Allocates a c-type and casts the result to a pointer of that type.
?	REALLOC_N(var, c-type, n")
?	Reallocates n c-types and assigns the result to var, a pointer to a c-type.
type *?	ALLOCA_N(c-type, n")
?	Allocates memory for n objects of c-type on the stack---this memory will be automatically freed when the function that invokes ALLOCA_N returns.

創(chuàng)建擴展程序

寫完了需要的源代碼，我們需要編譯它，以使Ruby程序可以訪問它。我們可以把它編譯成共享的對象，在運行時候動態(tài)裝載；或者把它靜態(tài)的連接到Ruby解釋器本身。基本的過程都已眼：

• 在給定的目錄寫好源代碼。
• 創(chuàng)建 extconf.rb文件。
• 運行extconf.rb創(chuàng)建 Makefile，用來編譯C文件。
• 運行make。
• 運行 make install。

用 extconf.rb創(chuàng)建Makefile?

上面看到的創(chuàng)建一個Ruby擴展程序的過程中，主要的步驟是作為程序員寫的extconf.rb。在這個程序里，需要判斷當(dāng)前系統(tǒng)需要支持哪些特性，以及這些特性的位置。運行extconf.rb程序?qū)a(chǎn)生一個Makefile文件，這是一個根據(jù)用戶的需求和系統(tǒng)屬性定制文件。當(dāng)你運行make程序時，我們創(chuàng)建的擴展程序?qū)痪幾g（也可能被安裝到某個地方）。

最簡單的extconf.rb有可能只有兩行長，并且，對很多Ruby擴展程序來說，這兩行足夠了：

require?'mkmf' create_makefile("Test")

第一行引入了模塊"mkmf"，這個模塊有我們要用到的各種命令。第二行為擴展程序"Test"創(chuàng)建了一個Makefile文件。（注意"Test"是擴展程序的名字，而Makefile一直都是這個名字）。Test將會在這個目錄被編譯。

Let's say that we run this extconf.rb program in a directory containing a single source file, main.c. The result is a Makefile that will build our extension. On our system, this contains the following commands.

gcc?-fPIC?-I/usr/local/lib/ruby/1.6/i686-linux?-g?-O2??\ ??-c?main.c?-o?main.o gcc?-shared?-o?Test.so?main.o?-lc

The result of this compilation is Test.so, which may be dynamically linked into Ruby at runtime with ``require''. See how the mkmf commands have located platform-specific libraries and used compiler-specific options automatically. Pretty neat, eh?

Although this basic program works for many simple extensions, you may have to do some more work if your extension needs header files or libraries that aren't included in the default compilation environment, or if you conditionally compile code based on the presence of libraries or functions.

A common requirement is to specify nonstandard directories where include files and libraries may be found. This is a two-step process. First, your extconf.rb should contain one or more dir_config commands. This specifies a tag for a set of directories. Then, when you run the extconf.rb program, you tell mkmf where the corresponding physical directories are on the current system.

If extconf.rb contains the line dir_config( name ), then you give the location of the corresponding directories with the command-line options:

--with-name-include=directory

* Add directory/include to the compile command.

--with-name-lib=directory

* Add directory/lib to the link command.

If (as is common) your include and library directories are both subdirectories of some other directory, and (as is also common) they're called include and lib, you can take a shortcut:

--with-name-dir=directory

* Add directory/lib and directory/include to the link command and compile command, respectively.

There's a twist here. As well as specifying all these --with options when you run extconf.rb, you can also use the --with options that were specified when Ruby was built for your machine. This means you can find out the locations of libraries that are used by Ruby itself.

To make all this concrete, lets say you need to use libraries and include files for the CD jukebox we're developing. Your extconf.rb program might contain

require?'mkmf' dir_config('cdjukebox') #?..?more?stuff create_makefile("CDJukeBox")

You'd then run extconf.rb with something like:

%?ruby?extconf.rb?--with-cdjukebox-dir=/usr/local/cdjb

The generated Makefile would assume that the libraries were in /usr/local/cdjb/lib and the include files were in /usr/local/cdjb/include.

The dir_config command adds to the list of places to search for libraries and include files. It does not, however, link the libraries into your application. To do that, you'll need to use one or more have_library or find_library commands.

have_library looks for a given entry point in a named library. If it finds the entry point, it adds the library to the list of libraries to be used when linking your extension. find_library is similar, but allows you to specify a list of directories to search for the library.

require?'mkmf' dir_config('cdjukebox') have_library('cdjb',?'CDPlayerNew') create_makefile("CDJukeBox")

On some platforms, a popular library may be in one of several places. The X Window system, for example, is notorious for living in different directories on different systems. The find_library command will search a list of supplied directories to find the right one (this is different from have_library, which uses only configuration information for the search). For example, to create a Makefile that uses X Windows and a jpeg library, extconf.rb might contain

require?'mkmf' if?have_library("jpeg","jpeg_mem_init")?and ???find_library("X11",?"XOpenDisplay",?"/usr/X11/lib", ????????????????"/usr/X11R6/lib",?"/usr/openwin/lib") then ????create_makefile("XThing") else ????puts?"No?X/JPEG?support?available" end

We've added some additional functionality to this program. All of the mkmf commands return false if they fail. This means that we can write an extconf.rb that generates a Makefile only if everything it needs is present. The Ruby distribution does this so that it will try to compile only those extensions that are supported on your system.

You also may want your extension code to be able to configure the features it uses depending on the target environment. For example, our CD jukebox may be able to use a high-performance MP3 decoder if the end user has one installed. We can check by looking for its header file.

require?'mkmf' dir_config('cdjukebox') have_library('cdjb',?'CDPlayerNew') have_header('hp_mp3.h') create_makefile("CDJukeBox")

We can also check to see if the target environment has a particular function in any of the libraries we'll be using. For example, the setpriority call would be useful but isn't always available. We can check for it with:

require?'mkmf' dir_config('cdjukebox') have_func('setpriority') create_makefile("CDJukeBox")

Both have_header and have_func define preprocessor constants if they find their targets. The names are formed by converting the target name to uppercase and prepending ``HAVE_''. Your C code can take advantage of this using constructs such as:

#if?defined(HAVE_HP_MP3_H) #??include?<hp_mp3.h> #endif #if?defined(HAVE_SETPRIORITY) ??err?=?setpriority(PRIOR_PROCESS,?0,?-10) #endif

If you have special requirements that can't be met with all these mkmf commands, your program can directly add to the global variables $CFLAGS and $LFLAGS, which are passed to the compiler and linker, respectively.

靜態(tài)連接 Static Linking

最后，如果你的系統(tǒng)不支持動態(tài)連接，或者你想你的擴展程序靜態(tài)的連接到Ruby本身，編輯Ruby發(fā)行版本中的ext目錄下的Setup文件，把你的擴展程序的目錄加進去，然后重新編譯Ruby。在Setup文件中列出來的擴展程序都會被靜態(tài)的連接到Ruby可執(zhí)行程序。如果你不想支持任何動態(tài)連接，你可以編輯Setup文件讓它只包含一行：

option?nodynamic

Embedding a Ruby Interpreter

In addition to extending Ruby by adding C code, you can also turn the problem around and embed Ruby itself within your application. Here's an example.

#include?"ruby.h" main()?{ ??/*?...?our?own?application?stuff?...?*/ ??ruby_init(); ??ruby_script("embedded"); ??rb_load_file("start.rb"); ??while?(1)?{ ????if?(need_to_do_ruby)?{ ??????ruby_run(); ????} ????/*?...?run?our?app?stuff?*/ ??} }

To initialize the Ruby interpreter, you need to call ruby_init(). But on some platforms, you may need to take special steps before that:

#if?defined(NT) ??NtInitialize(&argc,?&argv); #endif #if?defined(__MACOS__)?&&?defined(__MWERKS__) ??argc?=?ccommand(&argv); #endif

See main.c in the Ruby distribution for any other special defines or setup needed for your platform.

Embedded Ruby API
void?	ruby_init(")
?	Sets up and initializes the interpreter. This function should be called before any other Ruby-related functions.
void?	ruby_options(int?argc, char?**argv")
?	Gives the Ruby interpreter the command-line options.
void?	ruby_script(char?*name")
?	Sets the name of the Ruby script (and $0) to name.
void?	rb_load_file(char?*file")
?	Loads the given file into the interpreter.
void?	ruby_run(")
?	Runs the interpreter.

You need to take some special care with exception handling; any Ruby calls you make at this top level should be protected to catch exceptions and handle them cleanly. rb_protect, rb_rescue, and related functions are documented on page 192.

For an example of embedding a Ruby interpreter within another program, see also eruby, which is described beginning on page 147.

Bridging Ruby to Other Languages

So far, we've discussed extending Ruby by adding routines written in C. However, you can write extensions in just about any language, as long as you can bridge the two languages with C. Almost anything is possible, including awkward marriages of Ruby and C++, Ruby and Java, and so on.

But you may be able to accomplish the same thing without resorting to C code. For example, you could bridge to other languages using middleware such as CORBA or COM. See the section on Windows automation beginning on page 164 for more details.

Ruby C Language API

Last, but by no means least, here are several C-level functions that you may find useful when writing an extension.

Some functions require an ID: you can obtain an ID for a string by using rb_intern and reconstruct the name from an ID by using rb_id2name.

As most of these C functions have Ruby equivalents that are already described in detail elsewhere in this book, the descriptions here will be brief.

Also note that the following listing is not complete. There are many more functions available---too many to document them all, as it turns out. If you need a method that you can't find here, check ``ruby.h'' or ``intern.h'' for likely candidates. Also, at or near the bottom of each source file is a set of method definitions that describe the binding from Ruby methods to C functions. You may be able to call the C function directly, or search for a wrapper function that calls the function you are looking for. The following list, based on the list in README.EXT, shows the main source files in the interpreter.

Ruby Language Core

class.c error.c eval.c gc.c object.c parse.y variable.c

Utility Functions

dln.c regex.c st.c util.c

Ruby Interpreter

dmyext.c inits.c keywords main.c ruby.c version.c

Base Library

array.c bignum.c compar.c dir.c enum.c file.c hash.c io.c marshal.c math.c numeric.c pack.c prec.c process.c random.c range.c re.c signal.c sprintf.c string.c struct.c time.c

Defining Objects
VALUE?	rb_define_class(char?*name, VALUE?superclass")
?	Defines a new class at the top level with the given name and superclass (for class Object, use rb_cObject).
VALUE?	rb_define_module(char?*name")
?	Defines a new module at the top level with the given name.
VALUE?	rb_define_class_under(VALUE?under, char?*name, VALUE?superclass")
?	Defines a nested class under the class or module under.
VALUE?	rb_define_module_under(VALUE?under, char?*name")
?	Defines a nested module under the class or module under.
void?	rb_include_module(VALUE?parent, VALUE?module")
?	Includes the given module into the class or module parent.
void?	rb_extend_object(VALUE?obj, VALUE?module")
?	Extends obj with module.
VALUE?	rb_require(const?char?*name")
?	Equivalent to ``require name.'' Returns Qtrue or Qfalse.

In some of the function definitions that follow, the parameter argc specifies how many arguments a Ruby method takes. It may have the following values.

argc	Function prototype
0..17	VALUE func(VALUE self, VALUE arg...)
	The C function will be called with this many actual arguments.
-1	VALUE func(int argc, VALUE *argv, VALUE self)
	The C function will be given a variable number of arguments passed as a C array.
-2	VALUE func(VALUE self, VALUE args)
	The C function will be given a variable number of arguments passed as a Ruby array.

In a function that has been given a variable number of arguments, you can use the C function rb_scan_args to sort things out (see below).

Defining Methods
void?	rb_define_method(VALUE?classmod, char?*name, VALUE(*func)(), int?argc")
?	Defines an instance method in the class or module classmod with the given name, implemented by the C function func and taking argc arguments.
void?	rb_define_module_function(VALUE?classmod, char?*name, VALUE(*func)(), int?argc)")
?	Defines a method in class classmod with the given name, implemented by the C function func and taking argc arguments.
void?	rb_define_global_function(char?*name, VALUE(*func)(), int?argc")
?	Defines a global function (a private method of Kernel) with the given name, implemented by the C function func and taking argc arguments.
void?	rb_define_singleton_method(VALUE?classmod, char?*name, VALUE(*func)(), int?argc")
?	Defines a singleton method in class classmod with the given name, implemented by the C function func and taking argc arguments.
int?	rb_scan_args(int?argcount, VALUE?*argv, char?*fmt, ...")
?	Scans the argument list and assigns to variables similar to scanf: fmt is a string containing zero, one, or two digits followed by some flag characters. The first digit indicates the count of mandatory arguments; the second is the count of optional arguments. A ``*'' means to pack the rest of the arguments into a Ruby array. A ``&'' means that an attached code block will be taken and assigned to the given variable (if no code block was given, Qnil will be assigned). After the fmt string, pointers to VALUE are given (as with scanf) to which the arguments are assigned. VALUE?name,?one,?two,?rest; rb_scan_args(argc,?argv,?"12",?&name,?&one,?&two); rb_scan_args(argc,?argv,?"1*",?&name,?&rest);
void?	rb_undef_method(VALUE?classmod, const?char?*name")
?	Undefines the given method name in the given classmod class or module.
void?	rb_define_alias(VALUE?classmod, const?char?*newname, const?char?*oldname")
?	Defines an alias for oldname in class or module classmod.

Defining Variables and Constants
void?	rb_define_const(VALUE?classmod, char?*name, VALUE?value")
?	Defines a constant in the class or module classmod, with the given name and value.
void?	rb_define_global_const(char?*name, VALUE?value")
?	Defines a global constant with the given name and value.
void?	rb_define_variable(const?char?*name, VALUE?*object")
?	Exports the address of the given object that was created in C to the Ruby namespace as name. From Ruby, this will be a global variable, so name should start with a leading dollar sign. Be sure to honor Ruby's rules for allowed variable names; illegally named variables will not be accessible from Ruby.
void?	rb_define_class_variable(VALUE?class, const?char?*name, VALUE?val")
?	Defines a class variable name (which must be specified with a ``@@'' prefix) in the given class, initialized to value.
void?	rb_define_virtual_variable(const?char?*name, VALUE(*getter)(), void(*setter)()")
?	Exports a virtual variable to Ruby namespace as the global $name. No actual storage exists for the variable; attempts to get and set the value will call the given functions with the prototypes: VALUE?getter(ID?id,?VALUE?*data, ?????????????struct?global_entry?*entry); void?setter(VALUE?value,?ID?id,?VALUE?*data, ????????????struct?global_entry?*entry); You will likely not need to use the entry parameter and can safely omit it from your function declarations.
void?	rb_define_hooked_variable(const?char?*name, VALUE?*variable, VALUE(*getter)(), void(*setter)()")
?	Defines functions to be called when reading or writing to variable. See also rb_define_virtual_variable.
void?	rb_define_readonly_variable(const?char?*name, VALUE?*value")
?	Same as rb_define_variable, but read-only from Ruby.
void?	rb_define_attr(VALUE?variable, const?char?*name, int?read, int?write")
?	Creates accessor methods for the given variable, with the given name. If read is nonzero, create a read method; if write is nonzero, create a write method.
void?	rb_global_variable(VALUE?*obj")
?	Registers the given address with the garbage collector.

Calling Methods
VALUE?	rb_funcall(VALUE?recv, ID?id, int?argc, ...")
?	Invokes the method given by id in the object recv with the given number of arguments argc and the arguments themselves (possibly none).
VALUE?	rb_funcall2(VALUE?recv, ID?id, int?argc, VALUE?*args")
?	Invokes the method given by id in the object recv with the given number of arguments argc and the arguments themselves given in the C array args.
VALUE?	rb_funcall3(VALUE?recv, ID?id, int?argc, VALUE?*args")
?	Same as rb_funcall2, but will not call private methods.
VALUE?	rb_apply(VALUE?recv, ID?name, int?argc, VALUE?args")
?	Invokes the method given by id in the object recv with the given number of arguments argc and the arguments themselves given in the Ruby Array args.
ID?	rb_intern(char?*name")
?	Returns an ID for a given name. If the name does not exist, a symbol table entry will be created for it.
char *?	rb_id2name(ID?id")
?	Returns a name for the given id.
VALUE?	rb_call_super(int?argc, VALUE?*args")
?	Calls the current method in the superclass of the current object.

Exceptions
void?	rb_raise(VALUE exception, const?char?*fmt, ...")
?	Raises an exception. The given string fmt and remaining arguments are interpreted as with printf.
void?	rb_fatal(const?char?*fmt, ...")
?	Raises a Fatal exception, terminating the process. No rescue blocks are called, but ensure blocks will be called. The given string fmt and remaining arguments are interpreted as with printf.
void?	rb_bug(const?char?*fmt, ...")
?	Terminates the process immediately---no handlers of any sort will be called. The given string fmt and remaining arguments are interpreted as with printf. You should call this function only if a fatal bug has been exposed. You don't write fatal bugs, do you?
void?	rb_sys_fail(const?char?*msg")
?	Raises a platform-specific exception corresponding to the last known system error, with the given msg.
VALUE?	rb_rescue(VALUE?(*body)(), VALUE?args, VALUE(*rescue)(), VALUE?rargs")
?	Executes body with the given args. If a StandardError exception is raised, then execute rescue with the given rargs.
VALUE?	rb_ensure(VALUE(*body)(), VALUE?args, VALUE(*ensure)(), VALUE?eargs")
?	Executes body with the given args. Whether or not an exception is raised, execute ensure with the given rargs after body has completed.
VALUE?	rb_protect(VALUE?(*body)(), VALUE?args, int?*result")
?	Executes body with the given args and returns nonzero in result if any exception was raised.
void?	rb_notimplement(")
?	Raises a NotImpError exception to indicate that the enclosed function is not implemented yet, or not available on this platform.
void?	rb_exit(int?status")
?	Exits Ruby with the given status. Raises a SystemExit exception and calls registered exit functions and finalizers.
void?	rb_warn(const?char?*fmt, ...")
?	Unconditionally issues a warning message to standard error. The given string fmt and remaining arguments are interpreted as with printf.
void?	rb_warning(const?char?*fmt, ...")
?	Conditionally issues a warning message to standard error if Ruby was invoked with the -w flag. The given string fmt and remaining arguments are interpreted as with printf.

Iterators
void?	rb_iter_break(")
?	Breaks out of the enclosing iterator block.
VALUE?	rb_each(VALUE?obj")
?	Invokes the each method of the given obj.
VALUE?	rb_yield(VALUE?arg")
?	Transfers execution to the iterator block in the current context, passing arg as an argument. Multiple values may be passed in an array.
int?	rb_block_given_p(")
?	Returns true if yield would execute a block in the current context---that is, if a code block was passed to the current method and is available to be called.
VALUE?	rb_iterate(VALUE?(*method)(), VALUE?args, VALUE?(*block)(), VALUE?arg2")
?	Invokes method with argument args and block block. A yield from that method will invoke block with the argument given to yield, and a second argument arg2.
VALUE?	rb_catch(const?char?*tag, VALUE?(*proc)(), VALUE?value")
?	Equivalent to Ruby catch.
void?	rb_throw(const?char?*tag , VALUE?value")
?	Equivalent to Ruby throw.

Accessing Variables
VALUE?	rb_iv_get(VALUE?obj, char?*name")
?	Returns the instance variable name (which must be specified with a ``@'' prefix) from the given obj.
VALUE?	rb_ivar_get(VALUE?obj, ID?name")
?	Returns the instance variable name from the given obj.
VALUE?	rb_iv_set(VALUE?obj, char?*name, VALUE?value")
?	Sets the value of the instance variable name (which must be specified with a ``@'' prefix) in the given obj to value. Returns value.
VALUE?	rb_ivar_set(VALUE?obj, ID?name, VALUE?value")
?	Sets the value of the instance variable name in the given obj to value. Returns value.
VALUE?	rb_gv_set(const?char?*name, VALUE?value")
?	Sets the global variable name (the ``$'' prefix is optional) to value. Returns value.
VALUE?	rb_gv_get(const?char?*name")
?	Returns the global variable name (the ``$'' prefix is optional).
void?	rb_cvar_set(VALUE?class, ID?name, VALUE?val")
?	Sets the class variable name in the given class to value.
VALUE?	rb_cvar_get(VALUE?class, ID?name")
?	Returns the class variable name from the given class.
int?	rb_cvar_defined(VALUE?class, ID?name")
?	Returns Qtrue if the given class variable name has been defined for class; otherwise, returns Qfalse.
void?	rb_cv_set(VALUE?class, const?char?*name, VALUE?val")
?	Sets the class variable name (which must be specified with a ``@@'' prefix) in the given class to value.
VALUE?	rb_cv_get(VALUE?class, const?char?*name")
?	Returns the class variable name (which must be specified with a ``@@'' prefix) from the given class.

Object Status
?	OBJ_TAINT(VALUE?obj")
?	Marks the given obj as tainted.
int?	OBJ_TAINTED(VALUE?obj")
?	Returns nonzero if the given obj is tainted.
?	OBJ_FREEZE(VALUE?obj")
?	Marks the given obj as frozen.
int?	OBJ_FROZEN(VALUE?obj")
?	Returns nonzero if the given obj is frozen.
?	Check_SafeStr(VALUE?str")
?	Raises SecurityError if current safe level > 0 and str is tainted, or a TypeError if str is not a T_STRING.
int?	rb_safe_level(")
?	Returns the current safe level.
void?	rb_secure(int?level")
?	Raises SecurityError if level <= current safe level.
void?	rb_set_safe_level(int?newlevel")
?	Sets the current safe level to newlevel.

Commonly Used Methods
VALUE?	rb_ary_new(")
?	Returns a new Array with default size.
VALUE?	rb_ary_new2(long?length")
?	Returns a new Array of the given length.
VALUE?	rb_ary_new3(long?length, ...")
?	Returns a new Array of the given length and populated with the remaining arguments.
VALUE?	rb_ary_new4(long?length, VALUE?*values")
?	Returns a new Array of the given length and populated with the C array values.
void?	rb_ary_store(VALUE?self, long?index, VALUE?value")
?	Stores value at index in array self.
VALUE?	rb_ary_push(VALUE?self, VALUE?value")
?	Pushes value onto the end of array self. Returns value.
VALUE?	rb_ary_pop(VALUE?self")
?	Removes and returns the last element from the array self.
VALUE?	rb_ary_shift(VALUE?self")
?	Removes and returns the first element from the array self.
VALUE?	rb_ary_unshift(VALUE?self, VALUE?value")
?	Pushes value onto the front of array self. Returns value.
VALUE?	rb_ary_entry(VALUE?self, long?index")
?	Returns array self's element at index.
int?	rb_respond_to(VALUE?self, ID?method")
?	Returns nonzero if self responds to method.
VALUE?	rb_thread_create(VALUE?(*func)(), void?*data")
?	Runs func in a new thread, passing data as an argument.
VALUE?	rb_hash_new(")
?	Returns a new, empty Hash.
VALUE?	rb_hash_aref(VALUE?self, VALUE?key")
?	Returns the element corresponding to key in self.
VALUE?	rb_hash_aset(VALUE?self, VALUE?key, VALUE?value")
?	Sets the value for key to value in self. Returns value.
VALUE?	rb_obj_is_instance_of(VALUE?obj, VALUE?klass")
?	Returns Qtrue if obj is an instance of klass.
VALUE?	rb_obj_is_kind_of(VALUE?obj, VALUE?klass")
?	Returns Qtrue if klass is the class of obj or class is one of the superclasses of the class of obj.
VALUE?	rb_str_new(const?char?*src, long?length")
?	Returns a new String initialized with length characters from src.
VALUE?	rb_str_new2(const?char?*src")
?	Returns a new String initialized with the null-terminated C string src.
VALUE?	rb_str_dup(VALUE?str")
?	Returns a new String object duplicated from str.
VALUE?	rb_str_cat(VALUE?self, const?char?*src, long?length")
?	Concatenates length characters from src onto the String self. Returns self.
VALUE?	rb_str_concat(VALUE?self, VALUE?other")
?	Concatenates other onto the String self. Returns self.
VALUE?	rb_str_split(VALUE?self, const?char?*delim")
?	Returns an array of String objects created by splitting self on delim.

---

Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright ? 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/)).

Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder.

Distribution of the work or derivative of the work in any standard (paper) book form is prohibited unless prior permission is obtained from the copyright holder.