对ListenSocket 的研究(四)

磨砺技术珠矶，践行数据之道，追求卓越价值  

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[作者：高健@博客园 luckyjackgao@gmail.com]

对postmaster.c 中的 readmask，rmask,nsocket等进行分析，可以看到：它们之间有如下的关系(与细节无关的代码省略)：

/*                                
 * Initialise the masks for select() for the ports we are listening on. 
 * Return the number of sockets to listen on.                                
 */                                
static int                                
initMasks(fd_set *rmask)                                
{                                
    int            maxsock = -1;                
    int            i;          
    FD_ZERO(rmask);           
    for (i = 0; i < MAXLISTEN; i++)                            
    {                            
        int fd = ListenSocket[i];
        if (fd == PGINVALID_SOCKET)                        
            break; 
        FD_SET(fd, rmask);     
        if (fd > maxsock)                        
            maxsock = fd;                    
    }                        
    return maxsock + 1;                            
}

和

static int                                
ServerLoop(void)                                                    
{                                        
    ......                             
    nSockets = initMasks(&readmask);    
    for (;;)                                    
    {                                    
        fd_set        rmask;                        
        int            selres;                    
                                        
        /*                                
         * Wait for a connection request to arrive.  
         * We wait at most one minute, to ensure that the other background 
         * tasks handled below get done even when no requests are arriving. 
         * If we are in PM_WAIT_DEAD_END state, then we don't want to accept 
         * any new connections, so we don't call select() at all; just sleep  
         * for a little bit with signals unblocked.                                
         */                                
        memcpy((char *) &rmask, (char *) &readmask, sizeof(fd_set));   
                                        
        PG_SETMASK(&UnBlockSig);       
        if (pmState == PM_WAIT_DEAD_END)                                
        {                                
            ...                            
        }                                
        else                                
        {                                
            ...                         
            selres = select(nSockets, &rmask, NULL, NULL, &timeout); 
        }                                
                                     
        /*                                
         * Block all signals until we wait again.  (This makes it safe for our  
         * signal handlers to do nontrivial work.)                                
         */                                
        PG_SETMASK(&BlockSig);                                
                                        
        /* Now check the select() result */                                
        if (selres < 0)                                
        {                                
            ...                            
        }                                
                                        
        /*                                
         * New connection pending on any of our sockets? If so, fork a child 
         * process to deal with it.                                
         */                                
        if (selres > 0)                                
        {                                
            ...                            
        }                             
        ...                                
    }                                    
}

可以看出来，nsocket就是用于监听网络通信的地 fd_set中的文件描述符最大值+1。
至于原始的文件描述符，就是来自于 ListenSocket数组。
为了进一步研究，还需要从源头上看ListenSocket是如何被赋值的。

[作者：高健@博客园 luckyjackgao@gmail.com]

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磨砺技术珠矶，践行数据之道，追求卓越价值