It has a parameter called backlog and it limits the maximum length of queue of pending list.
If I set backlog to 128, is it means no more than 128 packets can be handled by server?
If I have three computers and each of them send 40-50 packets to the server, the total number will over the limitation of backlog; is it same as a computer send 2xx packets to server?
And then, how to handle the exception on client that the limit of backlog reached in the server?
Since I have a testing:
1. PCA sends packets to PCA itself, said sends 1024 packets at a time, each packet contains 34 bytes.
2. PCA has both receiver and sender.
3. PCA send a order number to the reciever.
4. But sometimes, receiver received extra packets (1 or 2 more).
5. Once an extra message is received, the data received will like this:
Can you problem me a direction that how client knows the server has been reach the limit of backlog?
The structure of sender.
Code:
if ( ( sock = socket( PF_INET, SOCK_STREAM, IPPROTO_TCP ) ) != -1 ) {
if ( connect( sock, ( struct sockaddr * )&srvAddr, sizeof( srvAddr ) ) == 0 ) {
while ( 1 ) {
//....
if ( send( sock, sendBuf, MSG_SIZE, 0 ) != MSG_SIZE ) {
printf( "RX ERR!\n" );
break;
}
No recv and don't sender does not exit forever or error occrus!
}
}
The structure of receiver:
Code:
assert( setsockopt( servSock, SOL_SOCKET, SO_REUSEADDR, &s, sizeof( s ) ) == 0 );
/* Bind to the local address */
if (bind(servSock, (struct sockaddr *) &echoServAddr, sizeof(echoServAddr)) < 0)
puts("RX: bind() failed");
/* Mark the socket so it will listen for incoming connections */
if (listen(servSock, MAXPENDING) < 0)
puts("RX: listen() failed");
while ( 1 ) {
/* Set the size of the in-out parameter */
clntLen = sizeof(echoClntAddr);
/* Wait for a client to connect */
if ((clntSock = accept(servSock, (struct sockaddr *) &echoClntAddr,
&clntLen)) < 0)
puts("RX: accept() failed");
/* clntSock is connected to a client! */
printf("\tHandling client %s\n", inet_ntoa(echoClntAddr.sin_addr));
/* Create separate memory for client argument */
if ((threadArgs = (struct ThreadArgs *) malloc(sizeof(struct ThreadArgs))) == NULL) {
puts("malloc() failed");
exit( -1 );
}
threadArgs -> clntSock = clntSock;
/* Create client thread */
if (pthread_create(&threadID, NULL, ThreadMain, (void *) threadArgs) != 0) {
puts("pthread_create() failed");
exit( -1 );
}
}
Code:
static void HandleTCPClient( ... ) {
unsigned char echoBuffer[MSG_SIZE + 1]; /* Buffer for echo string */
int recvMsgSize; /* Size of received message */
int i;
/* Receive message from client */
if ((recvMsgSize = recv(clntSocket, echoBuffer, MSG_SIZE, 0)) < 0) {
puts("RX: recv() failed");
return;
}
/* Send received string and receive again until end of transmission */
while (recvMsgSize > 0) /* zero indicates end of transmission */
{
....
/* See if there is more data to receive */
if ( ( recvMsgSize = recv( clntSocket, echoBuffer, MSG_SIZE, 0 ) ) < 0 ) {
puts("RX: recv() failed");
return;
}
recvCount++;
}
close( clntSocket ); /* Close client socket */
}
It has a parameter called backlog and it limits the maximum length of queue of pending list.
If I set backlog to 128, is it means no more than 128 packets can be handled by server?
No, it means that no more than 128 pending connections can be waiting at once. 128 people somewhere on the internet that are doing connect(my_fd, your_server); and the server has told them "OK, wait in line".
Quote:
Can you problem me a direction that how client knows the server has been reach the limit of backlog?
I think the client will just get "connection refused" when the server already has the maximum number of pending connections waiting. Note that this is pending connections: It won't limit established connections for you, you have to do that yourself.
If the problem does not related with the listen(), it may be an interesting thing.
I sent 1024 packets to the server (a PC has both sender and receiver, that means, it send packets to itself).
When I Ctrl+C to close and reopen the program few times, the receiver may receive extra package and garbage; and some packets are missing.
If I send 65535 packets at a time, this problem happens more frequency.
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