今天抽空研究了下live555的任务实现：

TaskScheduler分为三种任务：socket handler,event handler,delay task。这三种任务的特点是，前两个加入执行队列后会一直存在，而delay task在执行完一次后会立即弃掉。

socket handler保存在队列BasicTaskScheduler0::HandlerSet* fHandlers中;

event handler保存在数组BasicTaskScheduler0::TaskFunc * fTriggeredEventHandlers[MAX_NUM_EVENT_TRIGGERS]中;

delay task保存在队列BasicTaskScheduler0::DelayQueue fDelayQueue中。

一.研究delaytask：

可以参考：http://www.cnblogs.com/nightwatcher/archive/2011/04/10/2011158.html

在学习操作delay task的函数之前，先研究下live555中的这个DelayQueue ：

1.  
   class DelayQueueEntry {
2.  
   public:
3.  
   virtual ~DelayQueueEntry();
4.  
    
5.  
   intptr_t token() {
6.  
   return fToken;
7.  
   }
8.  
    
9.  
   protected: // abstract base class
10.  
    DelayQueueEntry(DelayInterval delay);
11.  
     
12.  
    virtual void handleTimeout(); //执行超时任务;
13.  
     
14.  
    private:
15.  
    friend class DelayQueue;
16.  
    DelayQueueEntry* fNext; //后一个对象
17.  
    DelayQueueEntry* fPrev; //前一个对象
18.  
    DelayInterval fDeltaTimeRemaining; 超时时间（倒计时），该结构体含两个参数，一个是秒，一个是微秒;
19.  
     
20.  
    intptr_t fToken; //游标，方便查表
21.  
    static intptr_t tokenCounter; //队列计数器;
22.  
    };
23.  
     
24.  
     
25.  
    class DelayQueue: public DelayQueueEntry {
26.  
    public:
27.  
    DelayQueue();
28.  
    virtual ~DelayQueue();
29.  
     
30.  
    void addEntry(DelayQueueEntry* newEntry); // returns a token for the entry
31.  
    void updateEntry(DelayQueueEntry* entry, DelayInterval newDelay); //更新一个任务的超时时间
32.  
    void updateEntry(intptr_t tokenToFind, DelayInterval newDelay); //通过游标查找某个任务，再更新其超时时间
33.  
    void removeEntry(DelayQueueEntry* entry); // but doesn't delete it //将某个任务从队列从移除，但是不销毁该对象
34.  
    DelayQueueEntry* removeEntry(intptr_t tokenToFind); // but doesn't delete it /通过游标，将某个任务从队列从移除，但是不销毁该对象
35.  
     
36.  
    DelayInterval const& timeToNextAlarm(); //倒计时还剩多久时间
37.  
    void handleAlarm(); //将超时的任务移除，然后执行
38.  
     
39.  
    private:
40.  
    DelayQueueEntry* head() { return fNext; }
41.  
    DelayQueueEntry* findEntryByToken(intptr_t token);
42.  
    void synchronize(); //更新超时时间
43.  
     
44.  
    EventTime fLastSyncTime;
45.  
    };
46.  
     
47.  
     
48.  
     
49.  
    class AlarmHandler: public DelayQueueEntry {
50.  
    public:
51.  
    AlarmHandler(TaskFunc* proc, void* clientData, DelayInterval timeToDelay)
52.  
    : DelayQueueEntry(timeToDelay), fProc(proc), fClientData(clientData) {
53.  
    }
54.  
     
55.  
    private: // redefined virtual functions
56.  
    virtual void handleTimeout() {
57.  
    (*fProc)(fClientData); //通过调用函数指针 +参数　执行任务
58.  
    DelayQueueEntry::handleTimeout();
59.  
    }
60.  
     
61.  
    private:
62.  
    TaskFunc* fProc; //delaytask的函数指针
63.  
    void* fClientData; //delaytask的函数所需要的参数
64.  
    };

操作该队列的方法在BasicTaskScheduler0.h、BasicTaskScheduler0.cpp 中声明和实现：

1.  
   TaskToken BasicTaskScheduler0::scheduleDelayedTask(int64_t microseconds, TaskFunc* proc, void* clientData) {
2.  
     if (microseconds < 0) microseconds = 0;
3.  
     DelayInterval timeToDelay((long)(microseconds/1000000), (long)(microseconds%1000000));
4.  
     AlarmHandler* alarmHandler = new AlarmHandler(proc, clientData, timeToDelay); //创建一个AlarmHandler对象;
5.  
     fDelayQueue.addEntry(alarmHandler); //加入任务队列中;
6.  
    
7.  
     return (void*)(alarmHandler->token());//返回该任务在队列中的游标
8.  
   }
9.  
    
10.  
    void BasicTaskScheduler0::unscheduleDelayedTask(TaskToken& prevTask) {
11.  
      DelayQueueEntry* alarmHandler = fDelayQueue.removeEntry((intptr_t)prevTask);//根据任务对象的游标，将任务移除队列
12.  
      prevTask = NULL;
13.  
      delete alarmHandler;//销毁对象
14.  
    }

二.event handler

event handler是被存在数组中。数组大小固定等于32（#define MAX_NUM_EVENT_TRIGGERS 32），用EventTriggerId来表示数组中的项，EventTriggerId是一个32位整数，因为数组是32项，所以用EventTriggerId中的第n位置为1，则表明对应数组中的第n项。成员变量fTriggersAwaitingHandling也是EventTriggerId类型，它里面置1的那些位对应了数组中所有需要处理的项。这样做节省了内存和计算，但降低了可读性，呵呵，而且也不够灵活，只能支持32项或64项，其它数量不被支持。

1.  
   EventTriggerId BasicTaskScheduler0::createEventTrigger(TaskFunc* eventHandlerProc) {
2.  
   unsigned i = fLastUsedTriggerNum;
3.  
   EventTriggerId mask = fLastUsedTriggerMask;
4.  
    
5.  
   do {
6.  
   i = (i+1)%MAX_NUM_EVENT_TRIGGERS; //序号加一
7.  
   mask >>= 1; //mask右移一位，代表一个新的序号
8.  
   if (mask == 0) mask = 0x80000000; //默认为第32位为1
9.  
    
10.  
    if (fTriggeredEventHandlers[i] == NULL) {//如果数组的该位置没有存入数据，则将函数指针存入fTriggeredEventHandlers，数据位置空，触发事件时传入
11.  
    // This trigger number is free; use it:
12.  
    fTriggeredEventHandlers[i] = eventHandlerProc;
13.  
    fTriggeredEventClientDatas[i] = NULL; // sanity
14.  
     
15.  
    fLastUsedTriggerMask = mask; //记录最新的Mask和序号
16.  
    fLastUsedTriggerNum = i;
17.  
     
18.  
    return mask; //分配成功，返回项数
19.  
    }
20.  
    } while (i != fLastUsedTriggerNum);
21.  
     
22.  
    // All available event triggers are allocated; return 0 instead:
23.  
    return 0;
24.  
    }
25.  
     
26.  
    void BasicTaskScheduler0::deleteEventTrigger(EventTriggerId eventTriggerId) {
27.  
    fTriggersAwaitingHandling &=~ eventTriggerId;
28.  
     
29.  
    if (eventTriggerId == fLastUsedTriggerMask) { // common-case optimization:如果删除的事件正好是最后一个非空项，则直接将函数指针和参数置空;
30.  
    fTriggeredEventHandlers[fLastUsedTriggerNum] = NULL;
31.  
    fTriggeredEventClientDatas[fLastUsedTriggerNum] = NULL;
32.  
    } else {
33.  
    // "eventTriggerId" should have just one bit set.
34.  
    // However, we do the reasonable thing if the user happened to 'or' together two or more "EventTriggerId"s:
35.  
    EventTriggerId mask = 0x80000000;
36.  
    for (unsigned i = 0; i < MAX_NUM_EVENT_TRIGGERS; ++i) {
37.  
    if ((eventTriggerId&mask) != 0) { //通过移位，然后与操作比对，找出要删除的元素
38.  
    fTriggeredEventHandlers[i] = NULL;
39.  
    fTriggeredEventClientDatas[i] = NULL;
40.  
    }
41.  
    mask >>= 1;
42.  
    }
43.  
    }
44.  
    }
45.  
     
46.  
    void BasicTaskScheduler0::triggerEvent(EventTriggerId eventTriggerId, void* clientData) {
47.  
    // First, record the "clientData":
48.  
    if (eventTriggerId == fLastUsedTriggerMask) { // common-case optimization:
49.  
    fTriggeredEventClientDatas[fLastUsedTriggerNum] = clientData;
50.  
    } else {
51.  
    EventTriggerId mask = 0x80000000;
52.  
    for (unsigned i = 0; i < MAX_NUM_EVENT_TRIGGERS; ++i) {
53.  
    if ((eventTriggerId&mask) != 0) {
54.  
    fTriggeredEventClientDatas[i] = clientData; //事件触发时，传入函数的参数
55.  
     
56.  
    fLastUsedTriggerMask = mask;
57.  
    fLastUsedTriggerNum = i;
58.  
    }
59.  
    mask >>= 1;
60.  
    }
61.  
    }
62.  
     
63.  
    // Then, note this event as being ready to be handled.
64.  
    // (Note that because this function (unlike others in the library) can be called from an external thread, we do this last, to
65.  
    // reduce the risk of a race condition.)
66.  
    fTriggersAwaitingHandling |= eventTriggerId;
67.  
    }

最后在BasicTaskScheduler::SingleStep中执行该事件函数。

三.socket handler

先看下几个用到的结构体

1.  
   class HandlerDescriptor {
2.  
   HandlerDescriptor(HandlerDescriptor* nextHandler);
3.  
   virtual ~HandlerDescriptor();
4.  
    
5.  
   public:
6.  
   int socketNum;//套接字的序号;
7.  
   int conditionSet; //socket状态，有SOCKET_READABLE，SOCKET_WRITABLE，SOCKET_EXCEPTION三种;
8.  
   TaskScheduler::BackgroundHandlerProc* handlerProc;//事件执行的函数;
9.  
   void* clientData;//事件执行的函数的参数;
10.  
     
11.  
    private:
12.  
    // Descriptors are linked together in a doubly-linked list:
13.  
    friend class HandlerSet;
14.  
    friend class HandlerIterator;
15.  
    HandlerDescriptor* fNextHandler;//下一个节点;
16.  
    HandlerDescriptor* fPrevHandler;//上一个节点;
17.  
    };
18.  
     
19.  
    //Handlerset主要实现了一个HandlerDescriptort的双向链表，并实现了对链表的插入，查找，删除,移动的操作;
20.  
    class HandlerSet {
21.  
    public:
22.  
    HandlerSet();
23.  
    virtual ~HandlerSet();
24.  
     
25.  
    void assignHandler(int socketNum, int conditionSet, TaskScheduler::BackgroundHandlerProc* handlerProc, void* clientData);//插入;
26.  
    void clearHandler(int socketNum);//删除;
27.  
    void moveHandler(int oldSocketNum, int newSocketNum);//移动;
28.  
     
29.  
    private:
30.  
    HandlerDescriptor* lookupHandler(int socketNum);//查找;
31.  
     
32.  
    private:
33.  
    friend class HandlerIterator;
34.  
    HandlerDescriptor fHandlers;//HandlerDescriptort链表头部;
35.  
    };
36.  
     
37.  
    //主要实现在HandlerSet中的迭代容器;
38.  
    class HandlerIterator {
39.  
    public:
40.  
    HandlerIterator(HandlerSet& handlerSet);
41.  
    virtual ~HandlerIterator();
42.  
     
43.  
    HandlerDescriptor* next(); //返回set中的下一个HandlerDescriptor，并保存当前的查找位置;
44.  
    void reset();
45.  
     
46.  
    private:
47.  
    HandlerSet& fOurSet;
48.  
    HandlerDescriptor* fNextPtr;
49.  
    };

处理socket handler的函数：

1.  
   void BasicTaskScheduler
2.  
   ::setBackgroundHandling(int socketNum, int conditionSet, BackgroundHandlerProc* handlerProc, void* clientData) {
3.  
   if (socketNum < 0) return;
4.  
   FD_CLR((unsigned)socketNum, &fReadSet); //删除该套接字;
5.  
   FD_CLR((unsigned)socketNum, &fWriteSet); //删除该套接字;
6.  
   FD_CLR((unsigned)socketNum, &fExceptionSet); //删除该套接字;
7.  
   if (conditionSet == 0) { //将该套接字对应的节点从链表中删除;
8.  
   fHandlers->clearHandler(socketNum);
9.  
   if (socketNum+1 == fMaxNumSockets) {
10.  
    --fMaxNumSockets;
11.  
    }
12.  
    } else {
13.  
    fHandlers->assignHandler(socketNum, conditionSet, handlerProc, clientData);//将该节点加入双向链表;
14.  
    if (socketNum+1 > fMaxNumSockets) {
15.  
    fMaxNumSockets = socketNum+1;
16.  
    }
17.  
    if (conditionSet&SOCKET_READABLE) FD_SET((unsigned)socketNum, &fReadSet);//加入可读集合;
18.  
    if (conditionSet&SOCKET_WRITABLE) FD_SET((unsigned)socketNum, &fWriteSet);//加入可写集合;
19.  
    if (conditionSet&SOCKET_EXCEPTION) FD_SET((unsigned)socketNum, &fExceptionSet);//加入异常集合;
20.  
    }
21.  
    }
22.  
     
23.  
    void BasicTaskScheduler::moveSocketHandling(int oldSocketNum, int newSocketNum) {
24.  
    //先对套接字参数进行验证;
25.  
    if (oldSocketNum < 0 || newSocketNum < 0) return; // sanity check
26.  
    //根据老的套接字对应的集合，设置新套接字的集合;
27.  
    if (FD_ISSET(oldSocketNum, &fReadSet)) {FD_CLR((unsigned)oldSocketNum, &fReadSet); FD_SET((unsigned)newSocketNum, &fReadSet);}
28.  
    if (FD_ISSET(oldSocketNum, &fWriteSet)) {FD_CLR((unsigned)oldSocketNum, &fWriteSet); FD_SET((unsigned)newSocketNum, &fWriteSet);}
29.  
    if (FD_ISSET(oldSocketNum, &fExceptionSet)) {FD_CLR((unsigned)oldSocketNum, &fExceptionSet); FD_SET((unsigned)newSocketNum, &fExceptionSet);}
30.  
    //更新套接字;
31.  
    fHandlers->moveHandler(oldSocketNum, newSocketNum);
32.  
     
33.  
    if (oldSocketNum+1 == fMaxNumSockets) {
34.  
    --fMaxNumSockets;
35.  
    }
36.  
    if (newSocketNum+1 > fMaxNumSockets) {
37.  
    fMaxNumSockets = newSocketNum+1;
38.  
    }
39.  
    }