-- by caizj
调试c/c++程序，常用的有两种方式，一是打印日志调试，二是gdb调试，调试不仅可以定位问题，也可以用来熟悉代码。
首先，拿到一份陌生的代码，要先确定代码的大致结构，一些关键数据结构和方法，这里的技巧和经验不展开了
部分关键数据结构：
parse_def.h:
struct Selects;//查询相关
struct CreateTable;//建表相关
struct DropTable;//删表相关
enum SqlCommandFlag;//sql语句对应的command枚举
union Queries;//各类dml和ddl操作的联合
table.h
class Table;
db.h
class Db;部分关键接口
RC parse(const char *st, Query *sqln);//sql parse入口
ExecuteStage::handle_request
ExecuteStage::do_select
DefaultStorageStage::handle_event
DefaultHandler::create_index
DefaultHandler::insert_record
DefaultHandler::delete_record
DefaultHandler::update_record
Db::create_table
Db::find_table
Table::create
Table::scan_record
Table::insert_record
Table::update_record
Table::delete_record
Table::scan_record
Table::create_indexminiob提供的日志接口
deps/common/log/log.h:
#define LOG_PANIC(fmt, ...)
#define LOG_ERROR(fmt, ...)
#define LOG_WARN(fmt, ...)
#define LOG_INFO(fmt, ...)
#define LOG_DEBUG(fmt, ...)
#define LOG_TRACE(fmt, ...)日志相关配置项observer.ini
LOG_FILE_NAME = observer.log
# LOG_LEVEL_PANIC = 0,
# LOG_LEVEL_ERR = 1,
# LOG_LEVEL_WARN = 2,
# LOG_LEVEL_INFO = 3,
# LOG_LEVEL_DEBUG = 4,
# LOG_LEVEL_TRACE = 5,
# LOG_LEVEL_LAST
LOG_FILE_LEVEL=5
LOG_CONSOLE_LEVEL=1
调试工具有很多种，但是它们的关键点都是类似的，比如关联到进程、运行时查看变量值、单步运行、跟踪变量等。GDB是在Linux环境中常用的调试工具。其它环境上也有类似的工具，比如LLDB，或者Windows可能使用Visual Studio直接启动调试。Java的调试工具是jdb。
另外，很多同学喜欢使用Visual Studio Code(vscode)开发项目，vscode提供了很多插件，包括调试的插件，这些调试插件支持gdb、lldb等，可以按照自己的平台环境，设置不同的调试工具。
这里介绍了gdb的基本使用，其它工具的使用方法类似。
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Attach进程
[caizj@localhost run]$ gdb -p `pidof observer` GNU gdb (GDB) Red Hat Enterprise Linux 8.2-15.el8 Copyright (C) 2018 Free Software Foundation, Inc. (gdb) -
设置断点
(gdb) break do_select Breakpoint 1 at 0x44b636: file /home/caizj/source/stunning-engine/src/observer/sql/executor/execute_stage.cpp, line 526. (gdb) info b Num Type Disp Enb Address What 1 breakpoint keep y 0x000000000044b636 in ExecuteStage::do_select(char const*, Query*, SessionEvent*) at /home/caizj/source/stunning-engine/src/observer/sql/executor/execute_stage.cpp:526(gdb) break Table::scan_record Breakpoint 2 at 0x50b82b: Table::scan_record. (2 locations) (gdb) inf b Num Type Disp Enb Address What 1 breakpoint keep y 0x000000000044b636 in ExecuteStage::do_select(char const*, Query*, SessionEvent*) at /home/caizj/source/stunning-engine/src/observer/sql/executor/execute_stage.cpp:526 2 breakpoint keep y <MULTIPLE> 2.1 y 0x000000000050b82b in Table::scan_record(Trx*, ConditionFilter*, int, void*, void (*)(char const*, void*)) at /home/caizj/source/stunning-engine/src/observer/storage/common/table.cpp:421 2.2 y 0x000000000050ba00 in Table::scan_record(Trx*, ConditionFilter*, int, void*, RC (*)(Record*, void*)) at /home/caizj/source/stunning-engine/src/observer/storage/common/table.cpp:426 (gdb) -
继续执行
(gdb) c Continuing. -
触发断点
执行：miniob > select * from t1;
[Switching to Thread 0x7f51345f9700 (LWP 54706)] Thread 8 "observer" hit Breakpoint 1, ExecuteStage::do_select (this=0x611000000540, db=0x6040000005e0 "sys", sql=0x620000023080, session_event=0x608000003d20) at /home/caizj/source/stunning-engine/src/observer/sql/executor/execute_stage.cpp:526 526 RC rc = RC::SUCCESS; (gdb) -
单步调式
575 std::vector<TupleSet> tuple_sets; (gdb) next 576 for (SelectExeNode *&node: select_nodes) { (gdb) n 577 TupleSet tuple_set; (gdb) 578 rc = node->execute(tuple_set); (gdb) -
跳入 跟踪到函数内部
(gdb) s SelectExeNode::execute (this=0x60700002ce80, tuple_set=...) at /home/caizj/source/stunning-engine/src/observer/sql/executor/execution_node.cpp:43 43 CompositeConditionFilter condition_filter; (gdb) -
打印变量
(gdb) p tuple_set $3 = (TupleSet &) @0x7f51345f1760: {tuples_ = std::vector of length 0, capacity 0, schema_ = { fields_ = std::vector of length 0, capacity 0}} (gdb) -
watch变量
(gdb) n 443 RC rc = RC::SUCCESS; (gdb) n 444 RecordFileScanner scanner; (gdb) n 445 rc = scanner.open_scan(*data_buffer_pool_, file_id_, filter); (gdb) watch -l rc Hardware watchpoint 3: -location rc (gdb) c Continuing. Thread 8 "observer" hit Hardware watchpoint 3: -location rc Old value = SUCCESS New value = RECORD_EOF 0x000000000050c2de in Table::scan_record (this=0x60f000007840, trx=0x606000009920, filter=0x7f51345f12a0, limit=2147483647, context=0x7f51345f11c0, record_reader=0x50b74a <scan_record_reader_adapter(Record*, void*)>) at /home/caizj/source/stunning-engine/src/observer/storage/common/table.cpp:454 454 for ( ; RC::SUCCESS == rc && record_count < limit; rc = scanner.get_next_record(&record)) { (gdb) -
结束函数调用
(gdb) finish Run till exit from #0 0x000000000050c2de in Table::scan_record (this=0x60f000007840, trx=0x606000009920, filter=0x7f51345f12a0, limit=2147483647, context=0x7f51345f11c0, record_reader=0x50b74a <scan_record_reader_adapter(Record*, void*)>) at /home/caizj/source/stunning-engine/src/observer/storage/common/table.cpp:454 -
结束调试
(gdb) quit A debugging session is active. Inferior 1 [process 54699] will be detached. Quit anyway? (y or n) y Detaching from program: /home/caizj/local/bin/observer, process 54699 [Inferior 1 (process 54699) detached]