Mysql的Debug模式实现_MySQL

Mysql的Debug模式实现

前一段领导开发了一个内核的模块，测试的过程中，发现导致MYSQL客户端无法连接服务器。

经过查询文档，追根溯源，终于找到了MYSQL实现链接客户端的代码，在源文件sql-common/client.c里的 CLI_MYSQL_REAL_CONNECT 函数。

但是代码很长，一时半会儿肯定看不明白。这个时候发现，发现代码当中有很多这样的代码：

[cpp]

DBUG_ENTER("mysql_real_connect");

说明只要以调试模式启动MYSQL，就可以跟踪代码的执行。

经过查询文档和测试，只要在 cmake 的时候，增加参数 cmake -WITH_DEBUG=1 就可以了。

然后启动一个MYSQL客户端程序之前，更改一个环境变量：

[plain]

export MYSQL_DEBUG=d:t:O,/tmp/client.trace

使用编辑器打开 /tmp/client.trace 就会得到这样的Debug信息：

[cpp]

| info: Connect socket

| >vio_socket_connect

| | >vio_set_blocking

| |

| | >vio_io_wait

| |

| | >vio_set_blocking

| |

|

| info: No success, close socket, try next address.

| info: End of connect attempts, sock: 4 status: 1 error: 0

| error: Got error 0 on connect to 'localhost'

| >set_mysql_extended_error

| | enter: error :2003 'Can't connect to MySQL server on '%-.100s' (%d)'

|

| error: message: 2003/HY000 (Can't connect to MySQL server on 'localhost' (0))

后面的数字是行号。从这个文件就可以追踪程序的执行啦！

好牛逼啊！我们不禁感叹。之余，学习了一下这个调试模式的具体实现：

在 CMakeList.txt 中，有这么一段代码：

[plain]

IF(WITH_DEBUG)

SET(CMAKE_BUILD_TYPE "Debug" CACHE STRING ${BUILDTYPE_DOCSTRING} FORCE)

[plain]

IF(NOT CMAKE_BUILD_TYPE

AND NOT CMAKE_GENERATOR MATCHES "Visual Studio"

AND NOT CMAKE_GENERATOR MATCHES "Xcode")

# This is the case of no CMAKE_BUILD_TYPE choosen, typical for VS and Xcode

# or if custom C flags are set. In VS and Xcode for non-Debug configurations

# DBUG_OFF is already correctly set. Use DBUG_OFF for Makefile based projects

# without build type too, unless user specifically requests DBUG.

IF(NOT CMAKE_C_FLAGS MATCHES "-DDBUG_ON")

ADD_DEFINITIONS(-DDBUG_OFF)

ENDIF()

ENDIF()

如果没有设置 CMAKE_BUILD_TYPE ，那么就会执行下面一段代码。如果这时候也没有设置一个名为-DDBUG_ON的CFLAGS的环境变量的话，就会增加一个CFLAGS：-DDBUG_OFF。

之后，当编译器编译的时候，根据编译器的参数增加的宏来决定 怎么定义 DBUG_ENTER 之类的函数是空代码，还是实际的报错代码。

[cpp]

/*

* These macros provide a user interface into functions in the

* dbug runtime support library. They isolate users from changes

* in the MACROS and/or runtime support.

*

* The symbols "__LINE__" and "__FILE__" are expanded by the

* preprocessor to the current source file line number and file

* name respectively.

*

* WARNING --- Because the DBUG_ENTER macro allocates space on

* the user function's stack, it must precede any executable

* statements in the user function.

*

*/

# ifdef DBUG_OFF

# define DBUG_ENTER(a1)

# define DBUG_RETURN(a1) return(a1)

# define DBUG_VOID_RETURN return

# define DBUG_EXECUTE(keyword,a1)

# define DBUG_PRINT(keyword,arglist)

# define DBUG_2(keyword,format) /* Obsolete */

# define DBUG_3(keyword,format,a1) /* Obsolete */

# define DBUG_4(keyword,format,a1,a2) /* Obsolete */

# define DBUG_5(keyword,format,a1,a2,a3) /* Obsolete */

# define DBUG_PUSH(a1)

# define DBUG_POP()

# define DBUG_PROCESS(a1)

# define DBUG_FILE (stderr)

# define DBUG_SETJMP setjmp

# define DBUG_LONGJMP longjmp

# define DBUG_DUMP(keyword,a1)

# else

# define DBUG_ENTER(a) /

auto char *_db_func_; auto char *_db_file_; auto int _db_level_; /

auto char **_db_framep_; /

_db_enter_ (a,__FILE__,__LINE__,&_db_func_,&_db_file_,&_db_level_, /

&_db_framep_)

# define DBUG_LEAVE /

(_db_return_ (__LINE__, &_db_func_, &_db_file_, &_db_level_))

# define DBUG_RETURN(a1) return (DBUG_LEAVE, (a1))

# define DBUG_VOID_RETURN {DBUG_LEAVE; return;}

# define DBUG_EXECUTE(keyword,a1) /

{if (_db_on_) {if (_db_keyword_ (keyword)) { a1 }}}

# define DBUG_PRINT(keyword,arglist) /

{if (_db_on_) {_db_pargs_(__LINE__,keyword); _db_doprnt_ arglist;}}

# define DBUG_2(keyword,format) /

DBUG_PRINT(keyword,(format)) /* Obsolete */

# define DBUG_3(keyword,format,a1) /

DBUG_PRINT(keyword,(format,a1)) /* Obsolete */

# define DBUG_4(keyword,format,a1,a2) /

DBUG_PRINT(keyword,(format,a1,a2)) /* Obsolete */

# define DBUG_5(keyword,format,a1,a2,a3) /

DBUG_PRINT(keyword,(format,a1,a2,a3)) /* Obsolete */

# define DBUG_PUSH(a1) _db_push_ (a1)

# define DBUG_POP() _db_pop_ ()

# define DBUG_PROCESS(a1) (_db_process_ = a1)

# define DBUG_FILE (_db_fp_)

# define DBUG_SETJMP(a1) (_db_setjmp_ (), setjmp (a1))

# define DBUG_LONGJMP(a1,a2) (_db_longjmp_ (), longjmp (a1, a2))

# define DBUG_DUMP(keyword,a1,a2) _db_dump_(__LINE__,keyword,a1,a2)

# endif