1、Fastdfs的tracker

一、tracker主流程

本文使用FastDFS_v4.06版本。先参考一下这两篇文章，看看主流程做了哪些事:

http://blog.chinaunix.net/uid-20498361-id-3328763.html

http://yangbajing.blog.chinaunix.net/uid-26786622-id-3146373.html

二、tracker_service_init()

注意：它产生了四个工作线程，这些线程的启动是通过向它们各自的管道写数据来进行的。它们会检测到管道读事件（通过libevent），从而进一步调用recv_notify_read()。

int tracker_service_init()  //其中去除了错误处理部分{int result;struct tracker_thread_data *pThreadData;struct tracker_thread_data *pDataEnd;pthread_t tid;pthread_attr_t thread_attr;if ((result=init_pthread_lock(&tracker_thread_lock)) != 0) //设置线程锁{return result;}if ((result=init_pthread_lock(&lb_thread_lock)) != 0){return result;}if ((result=init_pthread_attr(&thread_attr, g_thread_stack_size)) != 0) //设置线程属性{}//初始化g_free_queue结构，并为对应的g_mpool分配内存（大小为256个（block_size+8192）,构成链表，256为最大连接数）。if ((result=free_queue_init(g_max_connections, TRACKER_MAX_PACKAGE_SIZE,\                TRACKER_MAX_PACKAGE_SIZE, sizeof(TrackerClientInfo))) != 0){return result;}//为每个线程分配一个线程结构，此处g_work_threads为4g_thread_data = (struct tracker_thread_data *)malloc(sizeof( \struct tracker_thread_data) * g_work_threads);if (g_thread_data == NULL){}g_tracker_thread_count = 0;pDataEnd = g_thread_data + g_work_threads;for (pThreadData=g_thread_data; pThreadData<pDataEnd; pThreadData++){pThreadData->ev_base = event_base_new(); //注意新版本libevent不再使用event_init()(非线程安全)if (pThreadData->ev_base == NULL){}if (pipe(pThreadData->pipe_fds) != 0){}#if defined(OS_LINUX)if ((result=fd_add_flags(pThreadData->pipe_fds[0], \O_NONBLOCK | O_NOATIME)) != 0){break;}#else#endif//创建线程，线程处理函数是work_thread_entrance(该函数将管道的可读事件添加到libevent中进行监听，该事件的处理函数为recv_notify_read).if ((result=pthread_create(&tid, &thread_attr, \work_thread_entrance, pThreadData)) != 0){break;}else{if ((result=pthread_mutex_lock(&tracker_thread_lock)) != 0){}g_tracker_thread_count++;if ((result=pthread_mutex_unlock(&tracker_thread_lock)) != 0){}}}pthread_attr_destroy(&thread_attr);return 0;}

三、sched_start

对于result=sched_start(&scheduleArray, &schedule_tid, g_thread_stack_size, (bool * volatile)&g_continue_flag)，sched_start 是开启线程sched_thread_entrance （sched_thread.c 260行），定期执行指定的任务；这些任务有log_sync_func、tracker_mem_check_alive、tracker_write_status_to_file。这三个函数以后再看。

static void *sched_thread_entrance(void *args){ScheduleContext *pContext;ScheduleEntry *pPrevious;ScheduleEntry *pCurrent;ScheduleEntry *pSaveNext;ScheduleEntry *pNode;ScheduleEntry *pUntil;int exec_count;int i;int sleep_time;pContext = (ScheduleContext *)args;if (sched_init_entries(&(pContext->scheduleArray)) != 0) //设置每个入口的next_call_time{free(pContext);return NULL;}sched_make_chain(pContext); //按照next_call_time将各个入口排序，并构成链表g_schedule_flag = true;while (*(pContext->pcontinue_flag)) //这个线程就一直在处理这个循环了。{sched_check_waiting(pContext); //在此等待有事务定时到达，并设置已到达定时的任务个数。if (pContext->scheduleArray.count == 0)  //no schedule entry{sleep(1);g_current_time = time(NULL);continue;}g_current_time = time(NULL);sleep_time = pContext->head->next_call_time - g_current_time;/*//fprintf(stderr, "count=%d, sleep_time=%d\n", \pContext->scheduleArray.count, sleep_time);*/while (sleep_time > 0 && *(pContext->pcontinue_flag)){sleep(1);g_current_time = time(NULL);if (sched_check_waiting(pContext) == 0){break;}sleep_time--;}if (!(*(pContext->pcontinue_flag))){break;}exec_count = 0;pCurrent = pContext->head;while (*(pContext->pcontinue_flag) && (pCurrent != NULL \&& pCurrent->next_call_time <= g_current_time)){//fprintf(stderr, "exec task id=%d\n", pCurrent->id);pCurrent->task_func(pCurrent->func_args); //调用入口函数处理任务pCurrent->next_call_time = g_current_time + \pCurrent->interval;pCurrent = pCurrent->next;exec_count++;}if (exec_count == 0 || pContext->scheduleArray.count == 1){continue;}if (exec_count > pContext->scheduleArray.count / 2) //如果有一半以上的任务到达定时了，则重新调整链表顺序。{sched_make_chain(pContext);continue;}pNode = pContext->head;    //如果只有少数几个定时到达，则用以下方法（逐个插入）处理链表顺序。pContext->head = pCurrent;  //new chain headfor (i=0; i<exec_count; i++){if (pNode->next_call_time >= pContext->tail->next_call_time){pContext->tail->next = pNode;pContext->tail = pNode;pNode = pNode->next;pContext->tail->next = NULL;continue;}pPrevious = NULL;pUntil = pContext->head;while (pUntil != NULL && \pNode->next_call_time > pUntil->next_call_time){pPrevious = pUntil;pUntil = pUntil->next;}pSaveNext = pNode->next;if (pPrevious == NULL){pContext->head = pNode;}else{pPrevious->next = pNode;}pNode->next = pUntil;pNode = pSaveNext;}}g_schedule_flag = false;logDebug("file: "__FILE__", line: %d, " \"schedule thread exit", __LINE__);free(pContext);return NULL;}

四、tracker_relationship_init-->relationship_thread_entrance

http://www3.xuebuyuan.com/1542033.html

tracker_relationship_init创建线程执行relationship_thread_entrance()。注意首次执行时，g_tracker_servers.servers为NULL

static void *relationship_thread_entrance(void* arg){#define MAX_SLEEP_SECONDS  10int fail_count;int sleep_seconds;fail_count = 0;while (g_continue_flag) //该线程在此不断循环。{sleep_seconds = 1;if (g_tracker_servers.servers != NULL){if (g_tracker_servers.leader_index < 0){if (relationship_select_leader() != 0){sleep_seconds = 1 + (int)((double)rand()* (double)MAX_SLEEP_SECONDS / RAND_MAX);}}else{if (relationship_ping_leader() == 0){fail_count = 0;}else{fail_count++;if (fail_count >= 3){g_tracker_servers.leader_index = -1;}}}}if (g_last_tracker_servers != NULL){tracker_mem_file_lock();free(g_last_tracker_servers);g_last_tracker_servers = NULL;tracker_mem_file_unlock();}sleep(sleep_seconds);}return NULL;}

五、log_set_cache(true)

设置g_log_contex->log_to_cache = 1，意味着write to buffer firstly, then sync to disk.

六、tracker_accept_loop(sock)

当有连接到来时，唤醒一个线程（向管道中写入incomesock），对应线程将会调用recv_notify_read()，见tracker_service_init()。

void tracker_accept_loop(int server_sock){int incomesock;struct sockaddr_in inaddr;socklen_t sockaddr_len;struct tracker_thread_data *pThreadData;while (g_continue_flag){sockaddr_len = sizeof(inaddr);incomesock = accept(server_sock, (struct sockaddr*)&inaddr, &sockaddr_len);if (incomesock < 0) //error{if (!(errno == EINTR || errno == EAGAIN)){}continue;}pThreadData = g_thread_data + incomesock % g_work_threads;if (write(pThreadData->pipe_fds[1], &incomesock, \sizeof(incomesock)) != sizeof(incomesock)){close(incomesock);}}}

七、后续工作

本文涉及的线程：主线程，4个工作线程，一个调度线程，一个选主线程。本文中尚未展开的函数，recv_notify_read()，三个调度任务函数，选主函数relationship_thread_entrance()，将在后续文章中剖析。与tracker主函数相关的其他一些处理函数可参考源代码。