From 902d86acbe01b0368771eb57873e09f2cfcd8184 Mon Sep 17 00:00:00 2001 From: Emiel Bruijntjes Date: Wed, 5 Mar 2014 12:13:54 +0100 Subject: default empty extension added, optimized Makefile --- documentation/loading-extensions.html | 286 ++++++++++++++++++++++++++++++++++ 1 file changed, 286 insertions(+) create mode 100644 documentation/loading-extensions.html (limited to 'documentation/loading-extensions.html') diff --git a/documentation/loading-extensions.html b/documentation/loading-extensions.html new file mode 100644 index 0000000..2556efd --- /dev/null +++ b/documentation/loading-extensions.html @@ -0,0 +1,286 @@ +
+ + +

How does PHP load its extensions?

+

+ You probably already know that native PHP extensions are compiled into *.so + files on unix-like systems, and *.dll files in Windows environments, and that + the global php.ini file holds a list of all extensions available on your system. + This means that if you're building your own extension, you are also going to + create such a *.so or *.dll file and you have to update the PHP + configuration file so that your own extension is loaded by PHP. +

+

Where to find your PHP configuration files?

+

+ If for one reason or another you can not find the PHP configuration file(s) + on your system, you can run the following command from the command line: +

+

+ 

+        php --ini
+
+

+

+ This will output a list of all configuration files that are loaded by PHP. + Extensions are enabled by adding "extension=name.so" lines to the + configuration file - where 'name' should of course be replaced by the name of + your extension. A default PHP installation already comes with many default + extensions, so in the configuration file(s) on your system you will certainly + find a number of these "extension=name.so" lines. +

+

+ The extension lines either take an absolute path ("extension=/path/to/extension.so") + or a relative path ("extension=extension.so"). If you'd like to use relative + paths, you must make sure that you've copied your extension *.so file to the + default extension directory, so that PHP can find it. To find out this default + extension directory, use the following command line instruction: +

+

+ 

+        php -i|grep extension_dir
+
+

+

+ The extension dir often has the form /usr/lib/php5/20121212 - or a different + date string depending on the PHP version you use. +

+ +

The get_module() startup function

+

+ Before we explain how you can create your own extension, we first explain + what PHP does to load an extension. When PHP starts, it loads the *.ini configuration + file(s) that we just described and for each "extension=name.so" line in these + files, it opens the appropriate library, and calls the "get_module()" + function from it. Each extension library (your extension too) must therefore + define and implement this "get_module()" C function. The function is called by + PHP right after the library is loaded (and thus way before pageviews are handled), + and it should return a memory address that points to a structure that holds information + about all functions, classes, variables and constants that are made available + by the extension. +

+

+ The structure that the get_module() returns is defined in the header files of + the Zend engine, but it is a pretty complicated structure without good documentation. + Luckily, the PHP-CPP library makes life easier for you, and offers an Extension + class that can be used instead. +

+

+ 

+        #include <phpcpp.h>
+        
+        /**
+         *  tell the compiler that the get_module is a pure C function
+         */
+        extern "C" {
+            
+            /**
+             *  Function that is called by PHP right after the PHP process
+             *  has started, and that returns an address of an internal PHP
+             *  strucure with all the details and features of your extension
+             *
+             *  @return void*   a pointer to an address that is understood by PHP
+             */
+            PHPCPP_EXPORT void *get_module() 
+            {
+                // static(!) Php::Extension object that should stay in memory
+                // for the entire duration of the process (that's why it's static)
+                static Php::Extension myExtension("my_extension", "1.0");
+                
+                // @todo    add your own functions, classes, namespaces to the extension
+                
+                // return the extension
+                return myExtension;
+            }
+        }
+
+

+

+ In the example above you see a very straightforward implementation of the + get_module() function. Every PHP extension that uses the PHP-CPP library + implements this function in a more or less similar way, and it is the + starting point of each extension. A number of elements require special attention. + For a start, the only header file that you see is the phpcpp.h header + file. If you're using the PHP-CPP library to build your own extensions, + you do not have to include the complicated, unstructured, and mostly undocumented + header files of the Zend engine - all you need is this single phpcpp.h header + file of the PHP-CPP library. If you insist, you are of course free to also + include the header files of the core PHP engine - but you do not have to. + PHP-CPP takes care of dealing with the internals of the PHP engine, and offers + you a simple to use API. +

+

+ The next thing that you'll notice it that we placed the get_module() function + inside an 'extern "C"' code block. As the name of the library already gives away, + PHP-CPP is a C++ library. However, PHP expects your library, and especially your + get_module() function, to be implemented in C and not in C++. That's why we've + wrapped the get_module() function in an 'extern "C"' block. This will instruct + the C++ compiler that the get_module() is a regular C function, and that it + should not apply any C++ name mangling to it. +

+

+ The PHP-CPP library defines a "PHPCPP_EXPORT" macro that should be placed + in front of the get_module() function. This macro makes sure that the get_module() + function is publicly exported, and thus callable by PHP. The macro has a different + implementation based on the compiler and operating system. +

+

+ This, by the way, is also the only macro that PHP-CPP offers. PHP-CPP intends to + be a very straightforward C++ library, without using magic or tricks from + pre-processors. What you see is what you get: If something looks like a + function, you can be sure that it actually IS a function, and when something + looks like a variable, you can be sure that it also IS a variable. +

+

+ Let's move on. Inside the get_module() function the Php::Extension object is + instantiated, and it is returned. It is crucial that you make a static + instance of this Php::Extension class, because the object must exist for the + entire lifetime of the PHP process, and not only for the duration of the get_module() + call. The constructor takes two arguments: the name of your extension and + its version number. +

+

+ The final step in the get_module() function is that the extension object + is returned. This may seem strange at first, because the get_module() function + is supposed to return a pointer-to-void, and not a full Php::Extension object. + Why does the compiler not complain about this? Well, the Php::Extension class + has a cast-to-void-pointer-operator. So although it seems that you're returning + the full extension object, in reality you only return a memory address that + points to a data structure that is understood by the core PHP engine and that + holds all the details of your extension. +

+

+ Note that the example above does not yet export any native functions or + native classes to PHP - it only creates the extension. That is going to be + the next step. +

+ + + +

Exporting native functions

+

+ An extension can of course only be useful if you define functions and/or + classes that can be accessed from PHP scripts. For functions you can do this + by adding your native function implementations to the Extension object: +

+

+ 

+        #include <phpcpp.h>
+        
+        extern void example1();
+        extern void example2(Php::Parameters &params);
+        extern Php::Value example3();
+        extern Php::Value example4(Php::Parameters &params);
+        
+        extern "C" {
+            PHPCPP_EXPORT void *get_module() {
+                static Php::Extension myExtension("my_extension", "1.0");
+                myExtension.add("native1", example1);
+                myExtension.add("native2", example2);
+                myExtension.add("native3", example3);
+                myExtension.add("native4", example4);
+                return myExtension.module();
+            }
+        }
+
+

+

+ What do we see here? We've added four function declarations ("example1", + "example2", "example3" and "example4") to the source code of our extension. + The reason why we've only declared the functions, and not fully implemented + them is to keep the example code relatively small. We assume that the + four example functions are implemented in a different file. In a real world + example you could just as well remove the "extern" keyword and implement the + four functions in the same source file as the get_module() call. +

+

+ The four functions all have a different signature: Some return a value, while + others do not return anything. And some take parameters, while others do not. + Despite the different signature of the functions, they can all be made + available in PHP by adding them to the extension object, by simply calling + the myExtension.add() method. This method takes two parameters: the name by + which the function should be accessible in PHP, and the actual native + function. +

+

+ In the example above we've used different names for the native functions + ("example1" up to "example4") as for the PHP functions ("native1" to + "native4"). This is legal - you do not have to use the same names for your + native functions as for your PHP functions. The following PHP script can be + used to call the four native functions: +

+

+ 

+        <?php
+        native1();
+        native2("a","b");
+        $x = native3();
+        $y = native4(1,2);
+        ?>
+
+

+

+ It is not possible to export every thinkable C/C++ function to the + PHP extension. Only functions that have one of the four supported signatures + can be exported: functions that return + void or a Php::Value object, and that either accept a Php::Parameters object + or no parameters at all, can be added to the extension object and can thus + be exported to PHP. +

+

Parameter types

+

+ PHP has a mechanism to enforce function parameters types, and to accept + parameters either by reference or by value. In the examples above, we have + not yet used that mechanism yes: it is up to the function implementations + themselves to inspect the 'Parameters' object, and check if the + variables are of the right type. +

+

+ However, the 'Extension::add()' method takes a third optional parameter that + you can use to specify the number of parameters that are supported, whether + the parameters are passed by reference or by value, and what the type of + the parameters is: +

+

+ 

+        #include <phpcpp.h>
+        
+        extern void example(Php::Parameters &params);
+        
+        extern "C" {
+            PHPCPP_EXPORT void *get_module() {
+                static Php::Extension myExtension("my_extension", "1.0");
+                myExtension.add("example", example, {
+                    Php::ByVal("a", Php::Type::Numeric),
+                    Php::ByVal("b", "ExampleClass"),
+                    Php::ByRef("c", "OtherClass")
+                });
+                return myExtension.module();
+            }
+        }
+
+

+

+ Above you see that we passed in additional information when we registered the + "example" function. We tell our extension that our function accepts three parameters: + the first parameter must be a regular number, while the other ones are object + instances of type "ExampleClass" and "OtherClass". In the end, your native C++ + "example" function will still be called with a Php::Parameters instance, but + the moment it gets called, you can be sure that the Php::Parameters object + will be filled with three members, and that two of them are objects of the + appropriate type, and that the third one is also passed by reference. +

+

Working with variables

+

+ Variables in PHP are non-typed. A variable can thus hold any possible type: + an integer, string, a floating point number, and even an object or an array. + C++ on the other hand is a typed language. In C++ an integer variable always + has a numeric value, and a string variable always hold a string value. +

+

+ When you mix native code and PHP code, you will need to convert the non-typed + PHP variables into native variables, and the other way round: convert native + variables back into non-typed PHP variables. The PHP-CPP library offers the + "Value" class that makes this a very simple task. +

+

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