You might want to use global C variables in your extension, either for your
own internal use or for receiving php.ini values of your extension’s registered
INI directives (INI is discussed in the next section). As PHP is designed to run
in multi-threaded environments, you shouldn’t define global variables on your
own. PHP supplies a mechanism that creates global variables for you, which
can be used both in threaded and non-threaded environments. You should
always use this mechanism and not define your own global variables. These
global variables are then accessed via a macro and used just as if they are reg-
ular global variables.
The ext_skel script that created your skeleton myfile project created the
necessary code to support global variables. By examining php_myfile.h, you
should see a commented section similar to the following:
ZEND_BEGIN_MODULE_GLOBALS(myfile)
int global_value;
char *global_string;
ZEND_END_MODULE_GLOBALS(myfile)
You can uncomment this section and add any global variables you’d like
in between the two macros. A few lines down in the file, you’ll see that the
skeleton script automatically defined a MYFILE_G(v) macro. This macro should
be used all over your source code to access these global variables. It will make
sure that if you’re in a multi-threaded environment, it will access a per-thread
copy of these globals. No mutual exclusion is required by you.
The last thing you need to do in order for the global variables to work is
to uncomment the following line in myfile.c:
ZEND_DECLARE_MODULE_GLOBALS(myfile)
You might want to initialize your global variables to a default value at
the beginning of each PHP request. In addition, if for example, the global vari-
ables point to allocated memory, you might also want to free the memory at
the end of each request. For this purpose, the global variable mechanism sup-
ports a special macro that allows you to register a constructor and destructor
function for your global variables (see Table 15.8 for an explanation of its
parameters):
ZEND_INIT_MODULE_GLOBALS(module_name, globals_ctor, globals_dtor)
Table 15.8 ZEND_INIT_MODULE_GLOBALS Macro Parameters
Parameter
Meaning
module_name
The name of your extension as passed to the
ZEND_BEGIN_MODULE_GLOBALS() macro. In our case, myfile.
globals_ctor
The constructor function pointer. In the myfile extension, the function
prototype would be something like
void php_myfile_init_globals(zend_myfile_globals
*myfile_globals)
globals_dtor
The destruction function pointer. For example,
void php_myfile_init_globals(zend_myfile_globals
*myfile_globals)
You can see an example of the constructor function and use of the
ZEND_INIT_MODULE_GLOBALS() macro in myfile.c.