MySQL 8 的 C++ 源码中，处理网络请求和 SQL 命令的流程涉及多个函数和类。以下是关键的函数和类，以及它们的作用：

1. do_command 函数

do_command 函数是 MySQL 服务器中处理客户端命令的核心函数。它从客户端读取一个命令并执行。这个函数在 sql/sql_parse.cc 文件中定义。

函数原型

cpp复制

bool do_command(THD *thd);

主要步骤

1. 初始化：

   • 清除可能的错误状态。

   • 设置线程的当前查询块为空。

   • 清除错误消息和诊断区域。

2. 读取命令：

   • 设置网络读取超时。

   • 调用 thd->get_protocol()->get_command 从客户端读取命令。

3. 处理命令：

   • 如果读取命令失败，处理错误并返回。

   • 否则，调用 dispatch_command 处理具体的命令。

4. 清理：

   • 无论成功还是失败，清理线程的资源和状态。

2. dispatch_command 函数

dispatch_command 函数根据客户端发送的命令类型（如 COM_QUERY、COM_STMT_PREPARE 等）调用相应的处理函数。这个函数也在 sql/sql_parse.cc 文件中定义。

函数原型

cpp复制

bool dispatch_command(THD *thd, COM_DATA *com_data, enum enum_server_command command);

主要步骤

1. 检查命令类型：

   • 根据命令类型调用相应的处理函数。例如：

     • COM_QUERY：调用 mysql_parse 解析和执行 SQL 查询。

     • COM_STMT_PREPARE：调用 mysql_parse 解析和准备预处理语句。

     • COM_QUIT：处理客户端断开连接。

2. 执行命令：

   • 调用相应的处理函数执行命令。

3. 返回结果：

   • 返回命令执行的结果。

3. handle_connection 函数

handle_connection 函数是处理新连接的线程函数。它在 sql/sql_connect.cc 文件中定义。这个函数负责初始化新连接的线程，并调用 do_command 处理客户端命令。

函数原型

cpp复制

extern "C" void *handle_connection(void *arg);

主要步骤

1. 初始化线程：

   • 初始化线程的资源和状态。

   • 设置线程的 TLS（线程局部存储）。

2. 处理连接：

   • 调用 do_command 处理客户端命令。

   • 如果客户端断开连接，清理线程的资源。

3. 清理线程：

   • 释放线程的资源。

   • 退出线程。

4. Connection_handler_manager 类

Connection_handler_manager 类负责管理连接处理程序。它在 sql/sql_connect.cc 文件中定义。这个类的主要职责包括：

• 接受新的连接。

• 创建新的线程来处理连接。

• 管理连接的生命周期。

主要方法

• process_new_connection：处理新的连接。

• add_connection：将新的连接添加到连接处理程序中。

##

/**Read one command from connection and execute it (query or simple command).This function is called in loop from thread function.For profiling to work, it must never be called recursively.@retval0  success@retval1  request of thread shutdown (see dispatch_command() description)
*/bool do_command(THD *thd) {bool return_value;int rc;NET *net = nullptr;enum enum_server_command command = COM_SLEEP;COM_DATA com_data;DBUG_TRACE;assert(thd->is_classic_protocol());/*indicator of uninitialized lex => normal flow of errors handling(see my_message_sql)*/thd->lex->set_current_query_block(nullptr);/*XXX: this code is here only to clear possible errors of init_connect.Consider moving to prepare_new_connection_state() instead.That requires making sure the DA is cleared before non-parsing statementssuch as COM_QUIT.*/thd->clear_error();  // Clear error messagethd->get_stmt_da()->reset_diagnostics_area();/*This thread will do a blocking read from the client whichwill be interrupted when the next command is received fromthe client, the connection is closed or "net_wait_timeout"number of seconds has passed.*/net = thd->get_protocol_classic()->get_net();my_net_set_read_timeout(net, thd->variables.net_wait_timeout);net_new_transaction(net);/*WL#15369 : to make connections threads sleep to test ifER_THREAD_STILL_ALIVE, and ER_NUM_THREADS_STILL_ALIVE arebeing logged in the intended way, i.e. when connection threadsare still alive, even after forcefully disconnecting them inclose_connections().*/DBUG_EXECUTE_IF("simulate_connection_thread_hang", sleep(15););/*Synchronization point for testing of KILL_CONNECTION.This sync point can wait here, to simulate slow code executionbetween the last test of thd->killed and blocking in read().The goal of this test is to verify that a connection does nothang, if it is killed at this point of execution.(Bug#37780 - main.kill fails randomly)Note that the sync point wait itself will be terminated by akill. In this case it consumes a condition broadcast, but doesnot change anything else. The consumed broadcast should notmatter here, because the read/recv() below doesn't use it.*/DEBUG_SYNC(thd, "before_do_command_net_read");/* For per-query performance counters with log_slow_statement */struct System_status_var query_start_status;thd->clear_copy_status_var();if (opt_log_slow_extra) {thd->copy_status_var(&query_start_status);}rc = thd->m_mem_cnt.reset();if (rc)thd->m_mem_cnt.set_thd_error_status();else {/*Because of networking layer callbacks in place,this call will maintain the following instrumentation:- IDLE events- SOCKET events- STATEMENT events- STAGE eventswhen reading a new network packet.In particular, a new instrumented statement is started.See init_net_server_extension()*/thd->m_server_idle = true;rc = thd->get_protocol()->get_command(&com_data, &command);thd->m_server_idle = false;}if (rc) {
#ifndef NDEBUGchar desc[VIO_DESCRIPTION_SIZE];vio_description(net->vio, desc);DBUG_PRINT("info", ("Got error %d reading command from socket %s",net->error, desc));
#endif  // NDEBUGMYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES(thd->m_statement_psi, false);/* Instrument this broken statement as "statement/com/error" */thd->m_statement_psi = MYSQL_REFINE_STATEMENT(thd->m_statement_psi, com_statement_info[COM_END].m_key);/* Check if we can continue without closing the connection *//* The error must be set. */assert(thd->is_error());thd->send_statement_status();/* Mark the statement completed. */MYSQL_END_STATEMENT(thd->m_statement_psi, thd->get_stmt_da());thd->m_statement_psi = nullptr;thd->m_digest = nullptr;if (rc < 0) {return_value = true;  // We have to close it.goto out;}net->error = NET_ERROR_UNSET;return_value = false;goto out;}#ifndef NDEBUGchar desc[VIO_DESCRIPTION_SIZE];vio_description(net->vio, desc);DBUG_PRINT("info", ("Command on %s = %d (%s)", desc, command,Command_names::str_notranslate(command).c_str()));expected_from_debug_flag = TDM::ANY;DBUG_EXECUTE_IF("tdon", { expected_from_debug_flag = TDM::ON; });DBUG_EXECUTE_IF("tdzero", { expected_from_debug_flag = TDM::ZERO; });DBUG_EXECUTE_IF("tdna", { expected_from_debug_flag = TDM::NOT_AVAILABLE; });
#endif  // NDEBUGDBUG_PRINT("info", ("packet: '%*.s'; command: %d",(int)thd->get_protocol_classic()->get_packet_length(),thd->get_protocol_classic()->get_raw_packet(), command));if (thd->get_protocol_classic()->bad_packet)assert(0);  // Should be caught earlier// Reclaim some memorythd->get_protocol_classic()->get_output_packet()->shrink(thd->variables.net_buffer_length);/* Restore read timeout value */my_net_set_read_timeout(net, thd->variables.net_read_timeout);DEBUG_SYNC(thd, "before_command_dispatch");return_value = dispatch_command(thd, &com_data, command);thd->get_protocol_classic()->get_output_packet()->shrink(thd->variables.net_buffer_length);out:/* The statement instrumentation must be closed in all cases. */assert(thd->m_digest == nullptr);assert(thd->m_statement_psi == nullptr);return return_value;
}

##

/**Perform one connection-level (COM_XXXX) command.@param thd             connection handle@param command         type of command to perform@param com_data        com_data union to store the generated command@todoset thd->lex->sql_command to SQLCOM_END here.@todoThe following has to be changed to an 8 byte integer@retval0   ok@retval1   request of thread shutdown, i. e. if command isCOM_QUIT
*/
bool dispatch_command(THD *thd, const COM_DATA *com_data,enum enum_server_command command) {assert(thd->lex->m_IS_table_stats.is_valid() == false);assert(thd->lex->m_IS_tablespace_stats.is_valid() == false);
#ifndef NDEBUGauto tabstat_grd = create_scope_guard([&]() {assert(thd->lex->m_IS_table_stats.is_valid() == false);assert(thd->lex->m_IS_tablespace_stats.is_valid() == false);});
#endif /* NDEBUG */bool error = false;Global_THD_manager *thd_manager = Global_THD_manager::get_instance();DBUG_TRACE;DBUG_PRINT("info", ("command: %d", command));Sql_cmd_clone *clone_cmd = nullptr;/* SHOW PROFILE instrumentation, begin */
#if defined(ENABLED_PROFILING)thd->profiling->start_new_query();
#endif/* Performance Schema Interface instrumentation, begin */thd->m_statement_psi = MYSQL_REFINE_STATEMENT(thd->m_statement_psi, com_statement_info[command].m_key);thd->set_command(command);/*Commands which always take a long time are logged intothe slow log only if opt_log_slow_admin_statements is set.*/thd->enable_slow_log = true;thd->lex->sql_command = SQLCOM_END; /* to avoid confusing VIEW detectors *//*KILL QUERY may come after cleanup in mysql_execute_command(). Next queryexecution is interrupted due to this. So resetting THD::killed here.THD::killed value can not be KILL_TIMEOUT here as timer used for statementmax execution time is disarmed in the cleanup stage ofmysql_execute_command. KILL CONNECTION should terminate the connection.Hence resetting THD::killed only for KILL QUERY case here.*/if (thd->killed == THD::KILL_QUERY) thd->killed = THD::NOT_KILLED;thd->set_time();if (is_time_t_valid_for_timestamp(thd->query_start_in_secs()) == false) {/*If the time has gone past end of epoch we need to shutdown the server. Butthere is possibility of getting invalid time value on some platforms.For example, gettimeofday() might return incorrect value on solarisplatform. Hence validating the current time with 5 iterations beforeinitiating the normal server shutdown process because of time gettingpast 2038.*/const int max_tries = 5;LogErr(WARNING_LEVEL, ER_CONFIRMING_THE_FUTURE, max_tries);int tries = 0;while (++tries <= max_tries) {thd->set_time();if (is_time_t_valid_for_timestamp(thd->query_start_in_secs()) == true) {LogErr(WARNING_LEVEL, ER_BACK_IN_TIME, tries);break;}LogErr(WARNING_LEVEL, ER_FUTURE_DATE, tries);}if (tries > max_tries) {/*If the time has got past epoch, we need to shut this server down.We do this by making sure every command is a shutdown and wehave enough privileges to shut the server downTODO: remove this when we have full 64 bit my_time_t support*/LogErr(ERROR_LEVEL, ER_UNSUPPORTED_DATE);const ulong master_access = thd->security_context()->master_access();thd->security_context()->set_master_access(master_access | SHUTDOWN_ACL);error = true;kill_mysql();}}thd->set_query_id(next_query_id());thd->reset_rewritten_query();thd_manager->inc_thread_running();if (!(server_command_flags[command] & CF_SKIP_QUESTIONS))thd->status_var.questions++;/**Clear the set of flags that are expected to be cleared at thebeginning of each command.*/thd->server_status &= ~SERVER_STATUS_CLEAR_SET;if (thd->get_protocol()->type() == Protocol::PROTOCOL_PLUGIN &&!(server_command_flags[command] & CF_ALLOW_PROTOCOL_PLUGIN)) {MYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES(thd->m_statement_psi, false);my_error(ER_PLUGGABLE_PROTOCOL_COMMAND_NOT_SUPPORTED, MYF(0));thd->killed = THD::KILL_CONNECTION;error = true;goto done;}/**Enforce password expiration for all RPC commands, except thefollowing:COM_QUERY/COM_STMT_PREPARE and COM_STMT_EXECUTE do a morefine-grained check later.COM_STMT_CLOSE and COM_STMT_SEND_LONG_DATA don't return anything.COM_PING only discloses information that the server is running,and that's available through other means.COM_QUIT should work even for expired statements.*/if (unlikely(thd->security_context()->password_expired() &&command != COM_QUERY && command != COM_STMT_CLOSE &&command != COM_STMT_SEND_LONG_DATA && command != COM_PING &&command != COM_QUIT && command != COM_STMT_PREPARE &&command != COM_STMT_EXECUTE)) {MYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES(thd->m_statement_psi, false);my_error(ER_MUST_CHANGE_PASSWORD, MYF(0));goto done;}if (mysql_event_tracking_command_notify(thd, AUDIT_EVENT(EVENT_TRACKING_COMMAND_START), command,Command_names::str_global(command).c_str())) {MYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES(thd->m_statement_psi, false);goto done;}/*For COM_QUERY,wait until query attributes are extracted.*/if (command != COM_QUERY) {MYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES(thd->m_statement_psi, false);}switch (command) {case COM_INIT_DB: {LEX_STRING tmp;thd->status_var.com_stat[SQLCOM_CHANGE_DB]++;thd->convert_string(&tmp, system_charset_info,com_data->com_init_db.db_name,com_data->com_init_db.length, thd->charset());const LEX_CSTRING tmp_cstr = {tmp.str, tmp.length};if (!mysql_change_db(thd, tmp_cstr, false)) {query_logger.general_log_write(thd, command, thd->db().str,thd->db().length);my_ok(thd);}break;}case COM_REGISTER_SLAVE: {// TODO: access of protocol_classic should be removedif (!register_replica(thd, thd->get_protocol_classic()->get_raw_packet(),thd->get_protocol_classic()->get_packet_length()))my_ok(thd);break;}case COM_RESET_CONNECTION: {thd->status_var.com_other++;thd->cleanup_connection();my_ok(thd);break;}case COM_CLONE: {thd->status_var.com_other++;/* Try loading clone plugin */clone_cmd = new (thd->mem_root) Sql_cmd_clone();if (clone_cmd && clone_cmd->load(thd)) {clone_cmd = nullptr;}thd->lex->m_sql_cmd = clone_cmd;thd->lex->sql_command = SQLCOM_CLONE;break;}case COM_SUBSCRIBE_GROUP_REPLICATION_STREAM: {Security_context *sctx = thd->security_context();if (!sctx->has_global_grant(STRING_WITH_LEN("GROUP_REPLICATION_STREAM")).first) {my_error(ER_SPECIFIC_ACCESS_DENIED_ERROR, MYF(0), "");error = true;break;}if (!error && call_gr_incoming_connection_cb(thd, thd->active_vio->mysql_socket.fd,thd->active_vio->ssl_arg? static_cast<SSL *>(thd->active_vio->ssl_arg): nullptr)) {my_error(ER_UNKNOWN_COM_ERROR, MYF(0));error = true;break;}my_ok(thd);break;}case COM_CHANGE_USER: {int auth_rc;thd->status_var.com_other++;thd->cleanup_connection();USER_CONN *save_user_connect =const_cast<USER_CONN *>(thd->get_user_connect());LEX_CSTRING save_db = thd->db();/*LOCK_thd_security_ctx protects the THD's security-context frominspection by SHOW PROCESSLIST while we're updating it. However,there is no need to protect this context while we're reading it,sinceother threads are not supposed to modify it.Nested acquiring of LOCK_thd_data is fine (see below).*/const Security_context save_security_ctx(*(thd->security_context()));MUTEX_LOCK(grd_secctx, &thd->LOCK_thd_security_ctx);auth_rc = acl_authenticate(thd, COM_CHANGE_USER);auth_rc |= mysql_event_tracking_connection_notify(thd, AUDIT_EVENT(EVENT_TRACKING_CONNECTION_CHANGE_USER));if (auth_rc) {*thd->security_context() = save_security_ctx;thd->set_user_connect(save_user_connect);thd->reset_db(save_db);my_error(ER_ACCESS_DENIED_CHANGE_USER_ERROR, MYF(0),thd->security_context()->user().str,thd->security_context()->host_or_ip().str,(thd->password ? ER_THD(thd, ER_YES) : ER_THD(thd, ER_NO)));thd->killed = THD::KILL_CONNECTION;error = true;} else {
#ifdef HAVE_PSI_THREAD_INTERFACE/* we've authenticated new user */PSI_THREAD_CALL(notify_session_change_user)(thd->get_psi());
#endif /* HAVE_PSI_THREAD_INTERFACE */if (save_user_connect) decrease_user_connections(save_user_connect);mysql_mutex_lock(&thd->LOCK_thd_data);my_free(const_cast<char *>(save_db.str));save_db = NULL_CSTR;mysql_mutex_unlock(&thd->LOCK_thd_data);}break;}case COM_STMT_EXECUTE: {/* Clear possible warnings from the previous command */thd->reset_for_next_command();Prepared_statement *stmt = nullptr;if (!mysql_stmt_precheck(thd, com_data, command, &stmt)) {PS_PARAM *parameters = com_data->com_stmt_execute.parameters;copy_bind_parameter_values(thd, parameters,com_data->com_stmt_execute.parameter_count);mysqld_stmt_execute(thd, stmt, com_data->com_stmt_execute.has_new_types,com_data->com_stmt_execute.open_cursor, parameters);thd->bind_parameter_values = nullptr;thd->bind_parameter_values_count = 0;}break;}case COM_STMT_FETCH: {/* Clear possible warnings from the previous command */thd->reset_for_next_command();Prepared_statement *stmt = nullptr;if (!mysql_stmt_precheck(thd, com_data, command, &stmt))mysqld_stmt_fetch(thd, stmt, com_data->com_stmt_fetch.num_rows);break;}case COM_STMT_SEND_LONG_DATA: {Prepared_statement *stmt;thd->get_stmt_da()->disable_status();if (!mysql_stmt_precheck(thd, com_data, command, &stmt))mysql_stmt_get_longdata(thd, stmt,com_data->com_stmt_send_long_data.param_number,com_data->com_stmt_send_long_data.longdata,com_data->com_stmt_send_long_data.length);break;}case COM_STMT_PREPARE: {/* Clear possible warnings from the previous command */thd->reset_for_next_command();Prepared_statement *stmt = nullptr;DBUG_EXECUTE_IF("parser_stmt_to_error_log", {LogErr(INFORMATION_LEVEL, ER_PARSER_TRACE,com_data->com_stmt_prepare.query);});DBUG_EXECUTE_IF("parser_stmt_to_error_log_with_system_prio", {LogErr(SYSTEM_LEVEL, ER_PARSER_TRACE, com_data->com_stmt_prepare.query);});if (!mysql_stmt_precheck(thd, com_data, command, &stmt))mysqld_stmt_prepare(thd, com_data->com_stmt_prepare.query,com_data->com_stmt_prepare.length, stmt);break;}case COM_STMT_CLOSE: {Prepared_statement *stmt = nullptr;thd->get_stmt_da()->disable_status();if (!mysql_stmt_precheck(thd, com_data, command, &stmt))mysqld_stmt_close(thd, stmt);break;}case COM_STMT_RESET: {/* Clear possible warnings from the previous command */thd->reset_for_next_command();Prepared_statement *stmt = nullptr;if (!mysql_stmt_precheck(thd, com_data, command, &stmt))mysqld_stmt_reset(thd, stmt);break;}case COM_QUERY: {/*IMPORTANT NOTE:Every execution path for COM_QUERY should call onceMYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES()*/assert(thd->m_digest == nullptr);thd->m_digest = &thd->m_digest_state;thd->m_digest->reset(thd->m_token_array, max_digest_length);if (alloc_query(thd, com_data->com_query.query,com_data->com_query.length)) {MYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES(thd->m_statement_psi, false);break;  // fatal error is set}const char *packet_end = thd->query().str + thd->query().length;if (opt_general_log_raw)query_logger.general_log_write(thd, command, thd->query().str,thd->query().length);DBUG_PRINT("query", ("%-.4096s", thd->query().str));#if defined(ENABLED_PROFILING)thd->profiling->set_query_source(thd->query().str, thd->query().length);
#endifconst LEX_CSTRING orig_query = thd->query();Parser_state parser_state;if (parser_state.init(thd, thd->query().str, thd->query().length)) {MYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES(thd->m_statement_psi, false);break;}parser_state.m_input.m_has_digest = true;// we produce digest if it's not explicitly turned off// by setting maximum digest length to zeroif (get_max_digest_length() != 0)parser_state.m_input.m_compute_digest = true;// Initially, prepare and optimize the statement for the primary// storage engine. If an eligible secondary storage engine is// found, the statement may be reprepared for the secondary// storage engine later.const auto saved_secondary_engine = thd->secondary_engine_optimization();thd->set_secondary_engine_optimization(Secondary_engine_optimization::PRIMARY_TENTATIVELY);copy_bind_parameter_values(thd, com_data->com_query.parameters,com_data->com_query.parameter_count);/* This will call MYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES() */dispatch_sql_command(thd, &parser_state);// Check if the statement failed and needs to be restarted in// another storage engine.check_secondary_engine_statement(thd, &parser_state, orig_query.str,orig_query.length);thd->set_secondary_engine_optimization(saved_secondary_engine);DBUG_EXECUTE_IF("parser_stmt_to_error_log", {LogErr(INFORMATION_LEVEL, ER_PARSER_TRACE, thd->query().str);});DBUG_EXECUTE_IF("parser_stmt_to_error_log_with_system_prio", {LogErr(SYSTEM_LEVEL, ER_PARSER_TRACE, thd->query().str);});while (!thd->killed && (parser_state.m_lip.found_semicolon != nullptr) &&!thd->is_error()) {/*Multiple queries exits, execute them individually*/const char *beginning_of_next_stmt = parser_state.m_lip.found_semicolon;/* Finalize server status flags after executing a statement. */thd->update_slow_query_status();thd->send_statement_status();const std::string &cn = Command_names::str_global(command);mysql_event_tracking_general_notify(thd, AUDIT_EVENT(EVENT_TRACKING_GENERAL_STATUS),thd->get_stmt_da()->is_error() ? thd->get_stmt_da()->mysql_errno(): 0,cn.c_str(), cn.length());size_t length =static_cast<size_t>(packet_end - beginning_of_next_stmt);log_slow_statement(thd);thd->reset_copy_status_var();/* Remove garbage at start of query */while (length > 0 &&my_isspace(thd->charset(), *beginning_of_next_stmt)) {beginning_of_next_stmt++;length--;}/* PSI end */MYSQL_END_STATEMENT(thd->m_statement_psi, thd->get_stmt_da());thd->m_statement_psi = nullptr;thd->m_digest = nullptr;/* SHOW PROFILE end */
#if defined(ENABLED_PROFILING)thd->profiling->finish_current_query();
#endif/* SHOW PROFILE begin */
#if defined(ENABLED_PROFILING)thd->profiling->start_new_query("continuing");thd->profiling->set_query_source(beginning_of_next_stmt, length);
#endifmysql_thread_set_secondary_engine(false);/* PSI begin */thd->m_digest = &thd->m_digest_state;thd->m_digest->reset(thd->m_token_array, max_digest_length);thd->m_statement_psi = MYSQL_START_STATEMENT(&thd->m_statement_state, com_statement_info[command].m_key,thd->db().str, thd->db().length, thd->charset(), nullptr);THD_STAGE_INFO(thd, stage_starting);thd->set_query(beginning_of_next_stmt, length);thd->set_query_id(next_query_id());/*Count each statement from the client.*/thd->status_var.questions++;thd->set_time(); /* Reset the query start time. */parser_state.reset(beginning_of_next_stmt, length);thd->set_secondary_engine_optimization(Secondary_engine_optimization::PRIMARY_TENTATIVELY);/* TODO: set thd->lex->sql_command to SQLCOM_END here */dispatch_sql_command(thd, &parser_state);check_secondary_engine_statement(thd, &parser_state,beginning_of_next_stmt, length);thd->set_secondary_engine_optimization(saved_secondary_engine);}thd->bind_parameter_values = nullptr;thd->bind_parameter_values_count = 0;/* Need to set error to true for graceful shutdown */if ((thd->lex->sql_command == SQLCOM_SHUTDOWN) &&(thd->get_stmt_da()->is_ok()))error = true;DBUG_PRINT("info", ("query ready"));break;}case COM_FIELD_LIST:  // This isn't actually needed{char *fields;/* Locked closure of all tables */LEX_STRING table_name;LEX_STRING db;push_deprecated_warn(thd, "COM_FIELD_LIST","SHOW COLUMNS FROM statement");/*SHOW statements should not add the used tables to the list of tablesused in a transaction.*/MDL_savepoint mdl_savepoint = thd->mdl_context.mdl_savepoint();thd->status_var.com_stat[SQLCOM_SHOW_FIELDS]++;if (thd->copy_db_to(&db.str, &db.length)) break;thd->convert_string(&table_name, system_charset_info,(char *)com_data->com_field_list.table_name,com_data->com_field_list.table_name_length,thd->charset());const Ident_name_check ident_check_status =check_table_name(table_name.str, table_name.length);if (ident_check_status == Ident_name_check::WRONG) {/* this is OK due to convert_string() null-terminating the string */my_error(ER_WRONG_TABLE_NAME, MYF(0), table_name.str);break;} else if (ident_check_status == Ident_name_check::TOO_LONG) {my_error(ER_TOO_LONG_IDENT, MYF(0), table_name.str);break;}mysql_reset_thd_for_next_command(thd);lex_start(thd);/* Must be before we init the table list. */if (lower_case_table_names && !is_infoschema_db(db.str, db.length))table_name.length = my_casedn_str(files_charset_info, table_name.str);Table_ref table_list(db.str, db.length, table_name.str, table_name.length,table_name.str, TL_READ);/*Init Table_ref members necessary when the undelryingtable is view.*/table_list.query_block = thd->lex->query_block;thd->lex->query_block->m_table_list.link_in_list(&table_list,&table_list.next_local);thd->lex->add_to_query_tables(&table_list);if (is_infoschema_db(table_list.db, table_list.db_length)) {ST_SCHEMA_TABLE *schema_table =find_schema_table(thd, table_list.alias);if (schema_table) table_list.schema_table = schema_table;}if (!(fields =(char *)thd->memdup(com_data->com_field_list.query,com_data->com_field_list.query_length)))break;// Don't count end \0thd->set_query(fields, com_data->com_field_list.query_length - 1);query_logger.general_log_print(thd, command, "%s %s",table_list.table_name, fields);if (open_temporary_tables(thd, &table_list)) break;if (check_table_access(thd, SELECT_ACL, &table_list, true, UINT_MAX,false))break;thd->lex->sql_command = SQLCOM_SHOW_FIELDS;// See comment in opt_trace_disable_if_no_security_context_access()const Opt_trace_start ots(thd, &table_list, thd->lex->sql_command,nullptr, nullptr, 0, nullptr, nullptr);mysqld_list_fields(thd, &table_list, fields);thd->lex->cleanup(true);/* No need to rollback statement transaction, it's not started. */assert(thd->get_transaction()->is_empty(Transaction_ctx::STMT));close_thread_tables(thd);thd->mdl_context.rollback_to_savepoint(mdl_savepoint);if (thd->transaction_rollback_request) {/*Transaction rollback was requested since MDL deadlock wasdiscovered while trying to open tables. Rollback transactionin all storage engines including binary log and release alllocks.*/trans_rollback_implicit(thd);thd->mdl_context.release_transactional_locks();}thd->cleanup_after_query();thd->lex->destroy();break;}case COM_QUIT:/* Prevent results of the form, "n>0 rows sent, 0 bytes sent" */thd->set_sent_row_count(0);/* We don't calculate statistics for this command */query_logger.general_log_print(thd, command, NullS);// Don't give 'abort' message// TODO: access of protocol_classic should be removedif (thd->is_classic_protocol())thd->get_protocol_classic()->get_net()->error = NET_ERROR_UNSET;thd->get_stmt_da()->disable_status();  // Don't send anything backerror = true;                          // End serverbreak;case COM_BINLOG_DUMP_GTID:// TODO: access of protocol_classic should be removederror = com_binlog_dump_gtid(thd, (char *)thd->get_protocol_classic()->get_raw_packet(),thd->get_protocol_classic()->get_packet_length());break;case COM_BINLOG_DUMP:// TODO: access of protocol_classic should be removederror = com_binlog_dump(thd, (char *)thd->get_protocol_classic()->get_raw_packet(),thd->get_protocol_classic()->get_packet_length());break;case COM_REFRESH: {int not_used;push_deprecated_warn(thd, "COM_REFRESH", "FLUSH statement");/*Initialize thd->lex since it's used in many base functions, such asopen_tables(). Otherwise, it remains uninitialized and may cause crashduring execution of COM_REFRESH.*/lex_start(thd);thd->status_var.com_stat[SQLCOM_FLUSH]++;const ulong options = (ulong)com_data->com_refresh.options;if (trans_commit_implicit(thd)) break;thd->mdl_context.release_transactional_locks();if (check_global_access(thd, RELOAD_ACL)) break;query_logger.general_log_print(thd, command, NullS);
#ifndef NDEBUGbool debug_simulate = false;DBUG_EXECUTE_IF("simulate_detached_thread_refresh",debug_simulate = true;);if (debug_simulate) {/*Simulate a reload without a attached thread session.Provides a environment similar to that of when theserver receives a SIGHUP signal and reloads cachesand flushes tables.*/bool res;current_thd = nullptr;res = handle_reload_request(nullptr, options | REFRESH_FAST, nullptr,&not_used);current_thd = thd;if (res) break;} else
#endifif (handle_reload_request(thd, options, (Table_ref *)nullptr,&not_used))break;if (trans_commit_implicit(thd)) break;close_thread_tables(thd);thd->mdl_context.release_transactional_locks();thd->lex->destroy();my_ok(thd);break;}case COM_STATISTICS: {System_status_var current_global_status_var;ulong uptime;size_t length [[maybe_unused]];ulonglong queries_per_second1000;char buff[250];const size_t buff_len = sizeof(buff);query_logger.general_log_print(thd, command, NullS);thd->status_var.com_stat[SQLCOM_SHOW_STATUS]++;mysql_mutex_lock(&LOCK_status);calc_sum_of_all_status(&current_global_status_var);mysql_mutex_unlock(&LOCK_status);if (!(uptime = (ulong)(thd->query_start_in_secs() - server_start_time)))queries_per_second1000 = 0;elsequeries_per_second1000 = thd->query_id * 1000LL / uptime;length = snprintf(buff, buff_len - 1,"Uptime: %lu  Threads: %d  Questions: %lu  ""Slow queries: %llu  Opens: %llu  Flush tables: %lu  ""Open tables: %u  Queries per second avg: %u.%03u",uptime, (int)thd_manager->get_thd_count(),(ulong)thd->query_id,current_global_status_var.long_query_count,current_global_status_var.opened_tables,refresh_version, table_cache_manager.cached_tables(),(uint)(queries_per_second1000 / 1000),(uint)(queries_per_second1000 % 1000));// TODO: access of protocol_classic should be removed.// should be rewritten using store functionsif (thd->get_protocol_classic()->write(pointer_cast<const uchar *>(buff),length))break;if (thd->get_protocol()->flush()) break;thd->get_stmt_da()->disable_status();break;}case COM_PING:thd->status_var.com_other++;my_ok(thd);  // Tell client we are alivebreak;case COM_PROCESS_INFO:bool global_access;LEX_CSTRING db_saved;thd->status_var.com_stat[SQLCOM_SHOW_PROCESSLIST]++;push_deprecated_warn(thd, "COM_PROCESS_INFO","SHOW PROCESSLIST statement");global_access = (check_global_access(thd, PROCESS_ACL) == 0);if (!thd->security_context()->priv_user().str[0] && !global_access) break;query_logger.general_log_print(thd, command, NullS);db_saved = thd->db();DBUG_EXECUTE_IF("force_db_name_to_null", thd->reset_db(NULL_CSTR););mysqld_list_processes(thd, global_access ? NullS : thd->security_context()->priv_user().str,false, false);DBUG_EXECUTE_IF("force_db_name_to_null", thd->reset_db(db_saved););break;case COM_PROCESS_KILL: {push_deprecated_warn(thd, "COM_PROCESS_KILL","KILL CONNECTION/QUERY statement");if (thd_manager->get_thread_id() & (~0xfffffffful))my_error(ER_DATA_OUT_OF_RANGE, MYF(0), "thread_id", "mysql_kill()");else {thd->status_var.com_stat[SQLCOM_KILL]++;sql_kill(thd, com_data->com_kill.id, false);}break;}case COM_SET_OPTION: {thd->status_var.com_stat[SQLCOM_SET_OPTION]++;switch (com_data->com_set_option.opt_command) {case (int)MYSQL_OPTION_MULTI_STATEMENTS_ON:// TODO: access of protocol_classic should be removedthd->get_protocol_classic()->add_client_capability(CLIENT_MULTI_STATEMENTS);my_eof(thd);break;case (int)MYSQL_OPTION_MULTI_STATEMENTS_OFF:thd->get_protocol_classic()->remove_client_capability(CLIENT_MULTI_STATEMENTS);my_eof(thd);break;default:my_error(ER_UNKNOWN_COM_ERROR, MYF(0));break;}break;}case COM_DEBUG:thd->status_var.com_other++;if (check_global_access(thd, SUPER_ACL)) break; /* purecov: inspected */query_logger.general_log_print(thd, command, NullS);my_eof(thd);
#ifdef WITH_LOCK_ORDERLO_dump();
#endif /* WITH_LOCK_ORDER */break;case COM_SLEEP:case COM_CONNECT:         // Impossible herecase COM_TIME:            // Impossible from clientcase COM_DELAYED_INSERT:  // INSERT DELAYED has been removed.case COM_END:default:my_error(ER_UNKNOWN_COM_ERROR, MYF(0));break;}done:assert(thd->open_tables == nullptr ||(thd->locked_tables_mode == LTM_LOCK_TABLES));/* Finalize server status flags after executing a command. */thd->update_slow_query_status();if (thd->killed) thd->send_kill_message();thd->send_statement_status();/* After sending response, switch to clone protocol */if (clone_cmd != nullptr) {assert(command == COM_CLONE);error = clone_cmd->execute_server(thd);}if (command == COM_SUBSCRIBE_GROUP_REPLICATION_STREAM && !error) {wait_for_gr_connection_end(thd);}thd->rpl_thd_ctx.session_gtids_ctx().notify_after_response_packet(thd);if (!thd->is_error() && !thd->killed)mysql_event_tracking_general_notify(thd, AUDIT_EVENT(EVENT_TRACKING_GENERAL_RESULT), 0, nullptr, 0);const std::string &cn = Command_names::str_global(command);mysql_event_tracking_general_notify(thd, AUDIT_EVENT(EVENT_TRACKING_GENERAL_STATUS),thd->get_stmt_da()->is_error() ? thd->get_stmt_da()->mysql_errno() : 0,cn.c_str(), cn.length());/* command_end is informational only. The plugin cannot abortexecution of the command at this point. */mysql_event_tracking_command_notify(thd, AUDIT_EVENT(EVENT_TRACKING_COMMAND_END), command, cn.c_str());log_slow_statement(thd);THD_STAGE_INFO(thd, stage_cleaning_up);thd->reset_query();thd->set_command(COM_SLEEP);thd->set_proc_info(nullptr);thd->lex->sql_command = SQLCOM_END;/* Performance Schema Interface instrumentation, end */MYSQL_END_STATEMENT(thd->m_statement_psi, thd->get_stmt_da());thd->m_statement_psi = nullptr;thd->m_digest = nullptr;thd->reset_query_for_display();/* Prevent rewritten query from getting "stuck" in SHOW PROCESSLIST. */thd->reset_rewritten_query();thd_manager->dec_thread_running();/* Freeing the memroot will leave the THD::work_part_info invalid. */thd->work_part_info = nullptr;/*If we've allocated a lot of memory (compared to the default preallocationsize = 8192; note that we don't actually preallocate anymore), freeit so that one big query won't cause us to hold on to a lot of RAM forever.If not, keep the last block so that the next query will hopefully be able torun without allocating memory from the OS.The factor 5 is pretty much arbitrary, but ends up allowing threeallocations (1 + 1.5 + 1.5²) under the current allocation policy.*/constexpr size_t kPreallocSz = 40960;if (thd->mem_root->allocated_size() < kPreallocSz)thd->mem_root->ClearForReuse();elsethd->mem_root->Clear();/* SHOW PROFILE instrumentation, end */
#if defined(ENABLED_PROFILING)thd->profiling->finish_current_query();
#endifreturn error;
}

##

/**Parse an SQL command from a text string and pass the resulting AST to thequery executor.@param thd          Current session.@param parser_state Parser state.
*/void dispatch_sql_command(THD *thd, Parser_state *parser_state) {DBUG_TRACE;DBUG_PRINT("dispatch_sql_command", ("query: '%s'", thd->query().str));statement_id_to_session(thd);DBUG_EXECUTE_IF("parser_debug", turn_parser_debug_on(););mysql_reset_thd_for_next_command(thd);// It is possible that rewritten query may not be empty (in case of// multiqueries). So reset it.thd->reset_rewritten_query();lex_start(thd);thd->m_parser_state = parser_state;invoke_pre_parse_rewrite_plugins(thd);thd->m_parser_state = nullptr;// we produce digest if it's not explicitly turned off// by setting maximum digest length to zeroif (get_max_digest_length() != 0)parser_state->m_input.m_compute_digest = true;LEX *lex = thd->lex;const char *found_semicolon = nullptr;bool err = thd->get_stmt_da()->is_error();size_t qlen = 0;if (!err) {err = parse_sql(thd, parser_state, nullptr);if (!err) err = invoke_post_parse_rewrite_plugins(thd, false);found_semicolon = parser_state->m_lip.found_semicolon;qlen = found_semicolon ? (found_semicolon - thd->query().str): thd->query().length;/*We set thd->query_length correctly to not log several queries, when weexecute only first. We set it to not see the ';' otherwise it would getinto binlog and Query_log_event::print() would give ';;' output.*/if (!thd->is_error() && found_semicolon && (ulong)(qlen)) {thd->set_query(thd->query().str, qlen - 1);}}DEBUG_SYNC_C("sql_parse_before_rewrite");if (!err) {/*Rewrite the query for logging and for the Performance Schemastatement tables. (Raw logging happened earlier.)Sub-routines of mysql_rewrite_query() should try to only rewrite whennecessary (e.g. not do password obfuscation when query contains nopassword).If rewriting does not happen here, thd->m_rewritten_query is stillempty from being reset in alloc_query().*/if (thd->rewritten_query().length() == 0) mysql_rewrite_query(thd);if (thd->rewritten_query().length()) {lex->safe_to_cache_query = false;  // see comments belowthd->set_query_for_display(thd->rewritten_query().ptr(),thd->rewritten_query().length());} else if (thd->slave_thread) {/*In the slave, we add the information to pfs.events_statements_history,but not to pfs.threads, as that is what the test suite expects.*/MYSQL_SET_STATEMENT_TEXT(thd->m_statement_psi, thd->query().str,thd->query().length);} else {thd->set_query_for_display(thd->query().str, thd->query().length);}if (!(opt_general_log_raw || thd->slave_thread)) {if (thd->rewritten_query().length())query_logger.general_log_write(thd, COM_QUERY,thd->rewritten_query().ptr(),thd->rewritten_query().length());else {query_logger.general_log_write(thd, COM_QUERY, thd->query().str, qlen);}}}const bool with_query_attributes = (thd->bind_parameter_values_count > 0);MYSQL_NOTIFY_STATEMENT_QUERY_ATTRIBUTES(thd->m_statement_psi,with_query_attributes);DEBUG_SYNC_C("sql_parse_after_rewrite");if (!err) {thd->m_statement_psi = MYSQL_REFINE_STATEMENT(thd->m_statement_psi, sql_statement_info[thd->lex->sql_command].m_key);if (mqh_used && thd->get_user_connect() &&check_mqh(thd, lex->sql_command)) {if (thd->is_classic_protocol())thd->get_protocol_classic()->get_net()->error = NET_ERROR_UNSET;} else {if (!thd->is_error()) {/* Actually execute the query */if (found_semicolon) {lex->safe_to_cache_query = false;thd->server_status |= SERVER_MORE_RESULTS_EXISTS;}lex->set_trg_event_type_for_tables();int error [[maybe_unused]];if (unlikely((thd->security_context()->password_expired() ||thd->security_context()->is_in_registration_sandbox_mode()) &&lex->sql_command != SQLCOM_SET_PASSWORD &&lex->sql_command != SQLCOM_ALTER_USER)) {if (thd->security_context()->is_in_registration_sandbox_mode())my_error(ER_PLUGIN_REQUIRES_REGISTRATION, MYF(0));elsemy_error(ER_MUST_CHANGE_PASSWORD, MYF(0));error = 1;} else {resourcegroups::Resource_group *src_res_grp = nullptr;resourcegroups::Resource_group *dest_res_grp = nullptr;MDL_ticket *ticket = nullptr;MDL_ticket *cur_ticket = nullptr;auto mgr_ptr = resourcegroups::Resource_group_mgr::instance();const bool switched = mgr_ptr->switch_resource_group_if_needed(thd, &src_res_grp, &dest_res_grp, &ticket, &cur_ticket);error = mysql_execute_command(thd, true);if (switched)mgr_ptr->restore_original_resource_group(thd, src_res_grp,dest_res_grp);thd->resource_group_ctx()->m_switch_resource_group_str[0] = '\0';if (ticket != nullptr)mgr_ptr->release_shared_mdl_for_resource_group(thd, ticket);if (cur_ticket != nullptr)mgr_ptr->release_shared_mdl_for_resource_group(thd, cur_ticket);}}}} else {/*Log the failed raw query in the Performance Schema. This statement didnot parse, so there is no way to tell if it may contain a password of not.The tradeoff is:a) If we do log the query, a user typing by accident a broken querycontaining a password will have the password exposed. This is veryunlikely, and this behavior can be documented. Remediation is touse a new password when retyping the corrected query.b) If we do not log the query, finding broken queries in the clientapplication will be much more difficult. This is much more likely.Considering that broken queries can typically be generated by attempts atSQL injection, finding the source of the SQL injection is critical, so thedesign choice is to log the query text of broken queries (a).*/thd->set_query_for_display(thd->query().str, thd->query().length);/* Instrument this broken statement as "statement/sql/error" */thd->m_statement_psi = MYSQL_REFINE_STATEMENT(thd->m_statement_psi, sql_statement_info[SQLCOM_END].m_key);assert(thd->is_error());DBUG_PRINT("info",("Command aborted. Fatal_error: %d", thd->is_fatal_error()));}THD_STAGE_INFO(thd, stage_freeing_items);sp_cache_enforce_limit(thd->sp_proc_cache, stored_program_cache_size);sp_cache_enforce_limit(thd->sp_func_cache, stored_program_cache_size);thd->lex->destroy();thd->end_statement();thd->cleanup_after_query();assert(thd->change_list.is_empty());DEBUG_SYNC(thd, "query_rewritten");
}

##

extern "C" {
static void *handle_connection(void *arg) {Global_THD_manager *thd_manager = Global_THD_manager::get_instance();Connection_handler_manager *handler_manager =Connection_handler_manager::get_instance();Channel_info *channel_info = static_cast<Channel_info *>(arg);bool pthread_reused [[maybe_unused]] = false;if (my_thread_init()) {connection_errors_internal++;channel_info->send_error_and_close_channel(ER_OUT_OF_RESOURCES, 0, false);handler_manager->inc_aborted_connects();Connection_handler_manager::dec_connection_count();delete channel_info;my_thread_exit(nullptr);return nullptr;}for (;;) {THD *thd = init_new_thd(channel_info);if (thd == nullptr) {connection_errors_internal++;handler_manager->inc_aborted_connects();Connection_handler_manager::dec_connection_count();break;  // We are out of resources, no sense in continuing.}#ifdef HAVE_PSI_THREAD_INTERFACEif (pthread_reused) {/*Reusing existing pthread:Create new instrumentation for the new THD job,and attach it to this running pthread.*/PSI_thread *psi = PSI_THREAD_CALL(new_thread)(key_thread_one_connection,0 /* no sequence number */,thd, thd->thread_id());PSI_THREAD_CALL(set_thread_os_id)(psi);PSI_THREAD_CALL(set_thread)(psi);}
#endif#ifdef HAVE_PSI_THREAD_INTERFACE/* Find the instrumented thread */PSI_thread *psi = PSI_THREAD_CALL(get_thread)();/* Save it within THD, so it can be inspected */thd->set_psi(psi);
#endif /* HAVE_PSI_THREAD_INTERFACE */mysql_thread_set_psi_id(thd->thread_id());mysql_thread_set_psi_THD(thd);const MYSQL_SOCKET socket =thd->get_protocol_classic()->get_vio()->mysql_socket;mysql_socket_set_thread_owner(socket);thd_manager->add_thd(thd);if (thd_prepare_connection(thd))handler_manager->inc_aborted_connects();else {while (thd_connection_alive(thd)) {if (do_command(thd)) break;}end_connection(thd);}close_connection(thd, 0, false, false);thd->get_stmt_da()->reset_diagnostics_area();thd->release_resources();// Clean up errors now, before possibly waiting for a new connection.
#if OPENSSL_VERSION_NUMBER < 0x10100000LERR_remove_thread_state(0);
#endif /* OPENSSL_VERSION_NUMBER < 0x10100000L */thd_manager->remove_thd(thd);Connection_handler_manager::dec_connection_count();#ifdef HAVE_PSI_THREAD_INTERFACE/* Stop telemetry, while THD is still available. */if (psi != nullptr) {PSI_THREAD_CALL(abort_telemetry)(psi);}/* Decouple THD and the thread instrumentation. */thd->set_psi(nullptr);mysql_thread_set_psi_THD(nullptr);
#endif /* HAVE_PSI_THREAD_INTERFACE */delete thd;#ifdef HAVE_PSI_THREAD_INTERFACE/* Delete the instrumentation for the job that just completed. */PSI_THREAD_CALL(delete_current_thread)();
#endif /* HAVE_PSI_THREAD_INTERFACE */// Server is shutting down so end the pthread.if (connection_events_loop_aborted()) break;channel_info = Per_thread_connection_handler::block_until_new_connection();if (channel_info == nullptr) break;pthread_reused = true;if (connection_events_loop_aborted()) {// Close the channel and exit as server is undergoing shutdown.channel_info->send_error_and_close_channel(ER_SERVER_SHUTDOWN, 0, false);delete channel_info;channel_info = nullptr;Connection_handler_manager::dec_connection_count();break;}}my_thread_end();my_thread_exit(nullptr);return nullptr;
}
}  // extern "C"

##

bool Per_thread_connection_handler::add_connection(Channel_info *channel_info) {int error = 0;my_thread_handle id;DBUG_TRACE;// Simulate thread creation for test case before we check thread cacheDBUG_EXECUTE_IF("fail_thread_create", error = 1; goto handle_error;);if (!check_idle_thread_and_enqueue_connection(channel_info)) return false;/*There are no idle threads available to take up the newconnection. Create a new thread to handle the connection*/channel_info->set_prior_thr_create_utime();error =mysql_thread_create(key_thread_one_connection, &id, &connection_attrib,handle_connection, (void *)channel_info);
#ifndef NDEBUG
handle_error:
#endif  // !NDEBUGif (error) {connection_errors_internal++;if (!create_thd_err_log_throttle.log())LogErr(ERROR_LEVEL, ER_CONN_PER_THREAD_NO_THREAD, error);channel_info->send_error_and_close_channel(ER_CANT_CREATE_THREAD, error,true);Connection_handler_manager::dec_connection_count();return true;}Global_THD_manager::get_instance()->inc_thread_created();DBUG_PRINT("info", ("Thread created"));return false;
}

##gdb调试栈，处理客户端连接

(gdb) bt
#0  my_thread_create (thread=0x7ffde2e84658, attr=0x57cc6d05fd80 <connection_attrib>, func=0x57cc69d4da88 <pfs_spawn_thread(void*)>, arg=0x57cca0dc1ea0)at /home/yym/mysql8/mysql-8.1.0/mysys/my_thread.cc:80
#1  0x000057cc69d4dd3a in pfs_spawn_thread_vc (key=5, seqnum=0, thread=0x7ffde2e84658, attr=0x57cc6d05fd80 <connection_attrib>,start_routine=0x57cc67e0e643 <handle_connection(void*)>, arg=0x57cca10e5ca0) at /home/yym/mysql8/mysql-8.1.0/storage/perfschema/pfs.cc:3089
#2  0x000057cc67e0e010 in inline_mysql_thread_create (key=5, sequence_number=0, thread=0x7ffde2e84658, attr=0x57cc6d05fd80 <connection_attrib>,start_routine=0x57cc67e0e643 <handle_connection(void*)>, arg=0x57cca10e5ca0) at /home/yym/mysql8/mysql-8.1.0/include/mysql/psi/mysql_thread.h:139
#3  0x000057cc67e0ecaf in Per_thread_connection_handler::add_connection (this=0x57cca0c26e10, channel_info=0x57cca10e5ca0)at /home/yym/mysql8/mysql-8.1.0/sql/conn_handler/connection_handler_per_thread.cc:420
#4  0x000057cc67f73289 in Connection_handler_manager::process_new_connection (this=0x57cca028d4d0, channel_info=0x57cca10e5ca0)at /home/yym/mysql8/mysql-8.1.0/sql/conn_handler/connection_handler_manager.cc:260
#5  0x000057cc679ceea4 in Connection_acceptor<Mysqld_socket_listener>::connection_event_loop (this=0x57cca0d1f290)at /home/yym/mysql8/mysql-8.1.0/sql/conn_handler/connection_acceptor.h:65
#6  0x000057cc679bf5a3 in mysqld_main (argc=22, argv=0x57cc9ea287b8) at /home/yym/mysql8/mysql-8.1.0/sql/mysqld.cc:8355
#7  0x000057cc679aa4cd in main (argc=9, argv=0x7ffde2e84d68) at /home/yym/mysql8/mysql-8.1.0/sql/main.cc:25(gdb) bt
#0  handle_connection (arg=0x57cca10e5ca0) at /home/yym/mysql8/mysql-8.1.0/sql/conn_handler/connection_handler_per_thread.cc:252
#1  0x000057cc69d4dbdc in pfs_spawn_thread (arg=0x57cca0dc1ea0) at /home/yym/mysql8/mysql-8.1.0/storage/perfschema/pfs.cc:3043
#2  0x00007834cd694ac3 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
#3  0x00007834cd726850 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81