在阅读PHP源码的时候，会遇到很多诸如：CG()，EG() 这样的宏，如果不了解这些宏的意义，会给理解源码造成很大困难。

Zend引擎中有两个重要的全局变量结构体，就是Zend引擎关闭之前都会存在的变量：

typedef struct _zend_compiler_globals zend_compiler_globals;
typedef struct _zend_executor_globals zend_executor_globals;

/* Compiler */
#ifdef ZTS
# define CG(v) TSRMG(compiler_globals_id, zend_compiler_globals *, v)
int zendparse(void *compiler_globals);
#else
# define CG(v) (compiler_globals.v)
extern ZEND_API struct _zend_compiler_globals compiler_globals;
int zendparse(void);
#endif


/* Executor */
#ifdef ZTS
# define EG(v) TSRMG(executor_globals_id, zend_executor_globals *, v)
#else
# define EG(v) (executor_globals.v)
extern ZEND_API zend_executor_globals executor_globals;
#endif

EG 的含义就是 executor_globals，Zend执行器相关的全局变量；

这两个结构都包含了很多元素，对理解PHP内核有很重要的意义：

struct _zend_compiler_globals {
	zend_stack bp_stack;
	zend_stack switch_cond_stack;
	zend_stack foreach_copy_stack;
	zend_stack object_stack;
	zend_stack declare_stack;

	zend_class_entry *active_class_entry;

	/* variables for list() compilation */
	zend_llist list_llist;
	zend_llist dimension_llist;
	zend_stack list_stack;

	zend_stack function_call_stack;

	char *compiled_filename;

	int zend_lineno;
	int comment_start_line;
	char *heredoc;
	int heredoc_len;

	zend_op_array *active_op_array;

	HashTable *function_table;	/* function symbol table */
	HashTable *class_table;		/* class table */

	HashTable filenames_table;

	HashTable *auto_globals;

	zend_bool in_compilation;
	zend_bool short_tags;
	zend_bool asp_tags;
	zend_bool allow_call_time_pass_reference;

	zend_declarables declarables;

	/* For extensions support */
	zend_bool extended_info;	/* generate extension information for debugger/profiler */
	zend_bool handle_op_arrays;	/* run op_arrays through op_array handlers */

	zend_bool unclean_shutdown;

	zend_bool ini_parser_unbuffered_errors;

	zend_llist open_files;

	long catch_begin;

	struct _zend_ini_parser_param *ini_parser_param;

	int interactive;

	zend_uint start_lineno;
	zend_bool increment_lineno;

	znode implementing_class;

	zend_uint access_type;

	char *doc_comment;
	zend_uint doc_comment_len;

#ifdef ZEND_MULTIBYTE
	zend_encoding **script_encoding_list;
	int script_encoding_list_size;
	zend_bool detect_unicode;

	zend_encoding *internal_encoding;

	/* multibyte utility functions */
	zend_encoding_detector encoding_detector;
	zend_encoding_converter encoding_converter;
	zend_encoding_oddlen encoding_oddlen;
#endif /* ZEND_MULTIBYTE */

#ifdef ZTS
	HashTable **static_members;
	int last_static_member;
#endif
};


struct _zend_executor_globals {
	zval **return_value_ptr_ptr;

	zval uninitialized_zval;
	zval *uninitialized_zval_ptr;

	zval error_zval;
	zval *error_zval_ptr;

	zend_function_state *function_state_ptr;
	zend_ptr_stack arg_types_stack;

	/* symbol table cache */
	HashTable *symtable_cache[SYMTABLE_CACHE_SIZE];
	HashTable **symtable_cache_limit;
	HashTable **symtable_cache_ptr;

	zend_op **opline_ptr;

	HashTable *active_symbol_table;
	HashTable symbol_table;		/* main symbol table */

	HashTable included_files;	/* files already included */

	jmp_buf *bailout;

	int error_reporting;
	int orig_error_reporting;
	int exit_status;

	zend_op_array *active_op_array;

	HashTable *function_table;	/* function symbol table */
	HashTable *class_table;		/* class table */
	HashTable *zend_constants;	/* constants table */

	zend_class_entry *scope;

	zval *This;

	long precision;

	int ticks_count;

	zend_bool in_execution;
	HashTable *in_autoload;
	zend_function *autoload_func;
	zend_bool full_tables_cleanup;
	zend_bool ze1_compatibility_mode;

	/* for extended information support */
	zend_bool no_extensions;

#ifdef ZEND_WIN32
	zend_bool timed_out;
#endif

	HashTable regular_list;
	HashTable persistent_list;

	zend_ptr_stack argument_stack;

	int user_error_handler_error_reporting;
	zval *user_error_handler;
	zval *user_exception_handler;
	zend_stack user_error_handlers_error_reporting;
	zend_ptr_stack user_error_handlers;
	zend_ptr_stack user_exception_handlers;

	/* timeout support */
	int timeout_seconds;

	int lambda_count;

	HashTable *ini_directives;
	HashTable *modified_ini_directives;

	zend_objects_store objects_store;
	zval *exception;
	zend_op *opline_before_exception;

	struct _zend_execute_data *current_execute_data;

	struct _zend_module_entry *current_module;

	zend_property_info std_property_info;

	zend_bool active; 

	void *reserved[ZEND_MAX_RESERVED_RESOURCES];
};

PHP内核中重要的两个全局变量