[lwip-devel] [patch #8037] LWIP server fails if we connect multiple clients

[Krantip]

URL:
  <http://savannah.nongnu.org/patch/?8037>

                 Summary: LWIP server fails if we connect multiple clients
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: krantip
            Submitted on: Mon 29 Apr 2013 05:04:17 AM GMT
                Category: None
                Priority: 7 - High
                  Status: None
                 Privacy: Public
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None

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Details:

I am using LWIP stack version 4.0.My requirement is,connect minimim 50 clients
to lwip server using single thread.
Single client server is working fine,but if i connect 2-3 clients,then after
some time,I found , tcp_write out of memory error,because of TCP_SND_QUEUELEN
gets over.
I get below error,when it shows tcp-write error.
LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 3, ("tcp_write: too long queue %"U16_F" (max
%"U16_F")\n",
*************************************************************
MY opt.h settigs as below,
#define TCP_TMR_INTERVAL                250
#define TCP_SND_BUF                     5840
#TCP_MSS                                1460
#define MEM_SIZE                        64000
#define MEMP_NUM_TCP_PCB                16
#define MEMP_NUM_TCP_PCB_LISTEN         50
#define MEMP_NUM_TCP_SEG                50
#define TCP_WND                         (4 * TCP_MSS)
#define TCP_SND_QUEUELEN                ((4 * (TCP_SND_BUF) + (TCP_MSS -
1))/(TCP_MSS))
***************************************************************
My server code is as folllows,

signed int prvxMBTCPPortReceive(void *arg, struct tcp_pcb *pxPCB, struct pbuf
*p, signed int Err)
{

        unsigned char *pModbusHeader;
        u16_t len;
        signed int Error;
        tcp_nagle_disable(pxPCB);
        if( Err != ERR_OK )
        {
                return Err;
    }
    if( p == NULL )                                                             
                                                 // If pbuf is NULL then remote 
end has
closed connection.
        {
                prvvMBPortReleaseClient( pxPCB );
                return ERR_OK;
    }

        len = p->tot_len;
        pModbusHeader = p->payload;


        MODTCP1 = ((struct mod_tcp_hdr1 *)pModbusHeader);
        Trans_id = MODTCP1->trans_id;
        Proto_ID = MODTCP1->proto_id;
        Len = MODTCP1->len;
        tcp_recved(pxPCB, p->len);
        tcp_tmr();

        memcpy( Comm3Buff, pModbusHeader + 6, (unsigned short) *(pModbusHeader 
+ 5)
);
        ReceiveBuffLength3 = len - 6;
        ProcessSerialIntr3();

        MODTCP1 = ((struct mod_tcp_hdr1 *)&RxBuff[usTCPBufPos]);
        MODTCP1->trans_id = Trans_id;
        MODTCP1->proto_id = 0;
        MODTCP1->len =  htons((unsigned short)(FrameLength3-1));

        memcpy( &RxBuff[usTCPBufPos + 6], Comm3Buff, (unsigned short) 
(FrameLength3 -
1) );


        if( (Error = tcp_write( pxPCB, RxBuff, (unsigned short) 
(6+FrameLength3-1),
01 )) == ERR_OK )
        {
                ( void )tcp_output( pxPCB );                                    
                        //Make sure data gets sent immediately
        }
        else
        {
                prvvMBPortReleaseClient( pxPCB );                               
                        // Drop the connection in case of an
write error.
        }
        usTCPBufPos = 0;                                                        
                        // Reset the buffer
        pbuf_free( p );
        return ERR_OK;
}




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