PostgreSQL server端接收连接后fork进程

main->PostmasterMain->ServerLoop:        for(;;){                ...                //会阻塞在这，监视文件描述符的变化                selres = select(nSockets, &rmask, NULL, NULL, &timeout);                if (selres > 0){                        for (i = 0; i < MAXLISTEN; i++){                                //找一个有效的fd                                if (ListenSocket[i] == PGINVALID_SOCKET)                                        break;                                if (FD_ISSET(ListenSocket[i], &rmask)){                                        port = ConnCreate(ListenSocket[i]);->StreamConnection->accept                                        BackendStartup(port);//fork进程                                        |--     pid = fork_process();                                        |       if (pid == 0){//child                                        |               InitPostmasterChild();                                        |               ClosePostmasterPorts(false);                                        |               BackendInitialize(port);                                        |               //该函数不会返回                                        |               BackendRun(port);->PostgresMain：                                        |               |--     for (;;){                                        |               |               if (send_ready_for_query){                                        |               |                       ...                                        |               |                       ReadyForQuery(whereToSendOutput);->pq_flush();->internal_flush->secure_write->secure_raw_write->send                                        |               |                       send_ready_for_query = false;                                        |               |               }                                        |               |               firstchar = ReadCommand(&input_message);                                        |               |               switch(firstchar):{                                        |               |                       case 'Q':exec_simple_query(query_string);                                        |               |                       ...                                        |               |               }                                        |               |--     }                                        |       }                                        |       ...father                                        |--     return STATUS_OK                                           //关闭father socket                                        StreamClose(port->sock);                                        ConnFree(port);                                }                        }                }        }