APache的PHP模块启动

首先，了解一下每个Apache模块都会输出一个模块数据结构，其定义结构如下（以PHP模块为例）：

AP_MODULE_DECLARE_DATA module php5_module = {
        STANDARD20_MODULE_STUFF,
        create_php_config,              /* create per-directory config structure */
        merge_php_config,               /* merge per-directory config structures */
        NULL,                                   /* create per-server config structure */
        NULL,                                   /* merge per-server config structures */
        php_dir_cmds,                   /* command apr_table_t */
        php_ap2_register_hook   /* register hooks */
};

STANDARD20_MODULE_STUFF这个宏是必须的，这个宏在经过扩展以后，可以为编译后的模块载入服务器构建提供版本信息，在PHP的模块中，create_php_config函数创建目录配置结构，,merge_php_config合并目录配置结构，php_dir_cmds函数为模块配置相关指令，php_ap2_register_hook 注册模块的钩子程序，对这个结构体会在apache的模块中专门说明，在这里主要关注的是php_ap2_register_hook.这里定义的一些回调方法，会在Apache启动的时候直接调用。 

php_ap2_register_hook函数的实现在源码sapi/apache2handler/sapi_apache2.c文件中：

void php_ap2_register_hook(apr_pool_t *p)
{
        ap_hook_pre_config(php_pre_config, NULL, NULL, APR_HOOK_MIDDLE);
        ap_hook_post_config(php_apache_server_startup, NULL, NULL, APR_HOOK_MIDDLE);
        ap_hook_handler(php_handler, NULL, NULL, APR_HOOK_MIDDLE);
        ap_hook_child_init(php_apache_child_init, NULL, NULL, APR_HOOK_MIDDLE);
}

php_apache_server_startup函数也在同一个文件里面实现：

static int
php_apache_server_startup(apr_pool_t *pconf, apr_pool_t *plog, apr_pool_t *ptemp, server_rec *s)
{
        void *data = NULL;
        const char *userdata_key = "apache2hook_post_config";

        /* Apache will load, unload and then reload a DSO module. This
         * prevents us from starting PHP until the second load. */
        apr_pool_userdata_get(&data, userdata_key, s->process->pool);
        if (data == NULL) {
                /* We must use set() here and *not* setn(), otherwise the
                 * static string pointed to by userdata_key will be mapped
                 * to a different location when the DSO is reloaded and the
                 * pointers won't match, causing get() to return NULL when
                 * we expected it to return non-NULL. */
                apr_pool_userdata_set((const void *)1, userdata_key, apr_pool_cleanup_null, s->process->pool);
                return OK;
        }

        /* Set up our overridden path. */
        if (apache2_php_ini_path_override) {
                apache2_sapi_module.php_ini_path_override = apache2_php_ini_path_override;
        }
#ifdef ZTS
        tsrm_startup(1, 1, 0, NULL);
#endif
        sapi_startup(&apache2_sapi_module);
        apache2_sapi_module.startup(&apache2_sapi_module);
        apr_pool_cleanup_register(pconf, NULL, php_apache_server_shutdown, apr_pool_cleanup_null);
        php_apache_add_version(pconf);

        return OK;
}

在这个函数里会调用apache2_sapi_module.startup函数，而这个函数在前一篇博文 PHP内核-Apache2的SAPI 可以看到，它最终调用的是php_module_startup函数，

该函数在PHP的主要文件main/main.c文件中：

int php_module_startup(sapi_module_struct *sf, zend_module_entry *additional_modules, uint num_additional_modules)
{
        zend_utility_functions zuf;
        zend_utility_values zuv;
        int module_number=0;    /* for REGISTER_INI_ENTRIES() */
        char *php_os;
#ifdef ZTS
        zend_executor_globals *executor_globals;
        void ***tsrm_ls;

        php_core_globals *core_globals;
#endif
#if defined(PHP_WIN32) || (defined(NETWARE) && defined(USE_WINSOCK))
        WORD wVersionRequested = MAKEWORD(2, 0);
        WSADATA wsaData;
#endif
....................

        php_ini_register_extensions(TSRMLS_C);
        zend_startup_modules(TSRMLS_C);

        /* disable certain classes and functions as requested by php.ini */
        php_disable_functions(TSRMLS_C);