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 == PGINVALID_SOCKET)
break;
if (FD_ISSET(ListenSocket, &rmask)){
port = ConnCreate(ListenSocket);->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);
}
}
}
}
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