Programming :: Parallel Data Transfer Using Sockets
Feb 25, 2011
I am doing a project where 2 clients connect to server and communicate (chat) and transfer data one after other using sockets. I have working code for this in C language. Now our main aim is to create a communication link where two clients transfer multiple streams data parallely. To be more precise i want to transfer images files and audio files parallel at same time, so is it possible to send data parallel using one socket connection?
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Feb 4, 2011
NextPendingConnection () returns a new socket with respect to a new client. This new QSocket is passed to the connect () function which connects it to a SLOT 'xyz' with SIGNAL 'readyRead()'. Now in the SLOT 'xyz' how I am supposed to automate the monitoring of ALL connected sockets to see whether some data is available on them? One pathetic way would be to run all the sockets through a for loop and check each one of them for the data. Secondly, I read up on QSocketNotifier() here: [URL]. But I am not sure if that is the correct thing.
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Nov 29, 2010
I am coding a http server which has to send the file(s) such as images, .avi files, .mpeg, that the client is going to request. I have been trying of sending files through sockets.
char info [256];
bzero(info, 256);
//memset(&info,0,sizeof(info));
read(socket, info, 255);
write(socket, HTTP, 255);
FILE *fl= fopen(info,"rb");
fseek(fl, 0, SEEK_END);
long len = ftell(fl);
printf("largo: %ld", len);
unsigned char *ret = (char*) malloc(len);
fseek(fl, 0, SEEK_SET);
fread(ret, 1, len, fl);
However, it's supposed to be shown in Mozilla Firefox (as the client). But it is not doing it, so.. It's just not getting the complete file.
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Jul 24, 2010
I'm trying to add local sockets in my multi-threaded application in order to exchange data between threads. The only problem I got is that most of the information available on the net is related to internet oriented socket programming whileI want to perform local connections. got a thread that does the sniffing via libpcap. And I would like that thread to send each captured packet to a second thread that will analyse the packetof the thread implementations is written in separate .h file.Or maybe there is a more effective method of exchanging data between threads
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Dec 14, 2010
In posix multi threading, how to send thread1 local data to thread2...?
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Jan 24, 2011
What ubuntu server setup will work the best on a non web mostly data based via sockets (mysql php phpadmin) will be the easiest to use and what sockets to use? Lamp?
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Jun 25, 2010
I would like to send a data using one thread and receive a data using other thread by using a same socket connection using USD sockets. The calls i am using for sending and receiving are send(), recv(). let me know is it possible to send and receive the data parallel (Full duplex communication)?
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Oct 28, 2010
I am writing a code in Python where a socket client changes data with the server. That works nice if the connection is up. However it is also supposed to work offline. So I need to be able to detect if the connection is up before sending data, but I was not able to do so. A summary of the code is like that:
Code:
try:
socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socket.connect( (self.host, self.port) )
connected = True
except:
connected = False
if connected:
data = "some data byte"
try:
socket.send(data)
except:
connected=False
socket.close()
If I unplug the cable after the connection is ready then the socket sends data and does not detect the connection failure. What is amazing is that the client detects the connection failure just after the cable has been plugged again. Of course there is a loop in the code above and always that connected==False a new connection is made. How could the program detect the connection failure before sending data and then lead the code to an exception?
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Apr 22, 2010
I have been trying out serial and parallel data communication on Fedora 13 Beta. I can easily see the list of serial ports through:
Code:
setserial -g /dev/ttyS[0-3]
And can also write some data through:
Code:
ll > /dev/ttyS0
But I am unable to see parallel ports
I can see something like:
Code:
/dev/parport0
But when I try out:
ll > /dev/parport0
It throws error.
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Nov 18, 2010
Is there any way to implement a simple ping script in C (unix)? I'm programming simple OpenWRT scripts.
I have found some examples of ping in C:
[URL]
However, nothing happens, nothing is sent.
When I look at the code, in the portion where the socket is created, I can see that the socket is not binding to any interface:
Code:
if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1)
{
perror("socket");
exit(EXIT_FAILURE);
}
setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL, &optval, sizeof(int));
Instead, it uses "setsockopt" to set some options.
My guess is that it is trying to send packets over the eth0 interface instead over the wl0 (wireless) interface (which is the one I want to use to send pings).
Now, my question is: Is there any other way to send pings in C by binding to an interface?
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Jul 25, 2010
I need to create a C/C++ program in Linux that succeeds in detecting how many tcp-sockets and what tcp-sockets are created by the other processes in the system in a particular time interval (e.g., the interval time this application is running in). Then, I'd need to get some information like local/remote port number and local/remote ip address of each of these sockets.
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Aug 27, 2010
I am struggling a little on how to best approach this problem. I have wrote a server program that runs via xinetd, that obviously spits out data at the client end. Fairly straightforward stuff?There is a point in my server code where I need to display an image/gui i.e something that runs on X11 that prompts a user to perform a task on the display connected at the the server side.So far I have written a test program that displays some text at the client end and then launches the browser at the server end. I have also set the following export. Code: export DISPLAY=:0 and then goes on to launch my web browser. Works great when ran locally on the server and when I remotely telnet in to the server and run the code.
However when I try to run the same piece of code as a xinetd service the export seems to have zero affect and the client terminal window displays errors associated with there not being a X11 server running.The code launches fine when I create a socket to serverip:6556 it just the ability to display gui programs to another display that does not seem to be working.
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Feb 1, 2011
Can someone help me with this problem,trying to send a packet,using tcp/ip,the packet should look like this:
Code:
field 1: SOCKS protocol version, 1 byte (0x05 for this version)
field 2: status, 1 byte:
0x00 = request granted
0x01 = general failure
0x02 = connection not allowed by ruleset
0x03 = network unreachable
0x04 = host unreachable
0x05 = connection refused by destination host
0x06 = TTL expired
0x07 = command not supported / protocol error
0x08 = address type not supported
field 3: reserved, must be 0x00
field 4: address type, 1 byte:
0x01 = IPv4 address
0x03 = Domain name
0x04 = IPv6 address
field 5: destination address of
4 bytes for IPv4 address
1 byte of name length followed by the name for Domain name
16 bytes for IPv6 address
field 6: network byte order port number, 2 bytes
and this is my code:
Code:
int domainLen = strlen(domain);
char reply[domainLen + 7];
reply[0] = 5; // version
reply[1] = 0; // succed
reply[2] = 0; // reserved
reply[3] = 3; // its a domain
reply[4] = domainLen;; // lenght of domain
for(int j = 0; j < domainLen; ++j)
{
reply[j + 5] = domain[j];
}
reply[5 + domainLen] = 80; // port
reply[20] = '�';
Send(reply, sizeof(reply));
domain is "www.google.com". Am I doing it right ? I dont know much about bits.
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Jun 9, 2010
I have a problem creating my second socket in client file. the program was running well but when I try to add another socket to connect to the same server, I got a problem connecting to the first socket! it doesn't make sense. the original code was:
sockfd[i] = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd[i] < 0) error("(MAIN) - Error openning socket 1");
port_num[i] = portno;
bzero((char*) &serv_addr[i], sizeof(serv_addr[i]));
[Code].....
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Jun 9, 2010
I am using the API libpcap in order to filter the traffic of the port 53 from my PC ro other PCs, in other words the DNS traffic.I want to get more information about the DNS traffic that is being sent to the DNS server, in other words the queries. So far I have no idea how to read the information data or payload of the UDP package in order to read the content of the traffic for example if there is any PTR, A, MX, etc Resource Record.According to the RFC 1053 there is a header that is possible to use in order to easily get this info.
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Apr 20, 2010
I have a problem passing a file descriptor from one process to another.
I have two processes A and B. Both are running in different network and
filesystem namespaces, so it is impossible to use unix domain sockets or
net sockets to pass a file descriptor from process A to process B.
The usage of STREAMS is also impossible, as you can see in
fixunix.com/unix/84093-streams-pipes-ioctl-i_sendfd.html
[quotation begin]
Linux doesn't have STREAMS, which are the System V way
of doing this task. ...
[quotation end]
Are there additional possibilities for file descriptor passing like
using named pipes or something like that or does anybody know
a good workaround for this problem ?
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Nov 30, 2010
I have written a server application which has select for both incoming new client connection requests and incoming data from client. I am able to process incoming connection requests and client data.
For example, server has 8 clients connected to it. If client 3 disconnects from server, how will server come to know this client has disconnected and to close its client socket fd gracefully? Does server's select get data on that client socket fd as 'close' data or any error code in recv() function that notifies server to close this client socket fd? Also if client disconnects abruptly without sending close request to server, how should server handle this? Does server get "EPIPE" error?
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Jul 8, 2011
Hi, is it possible to send a request to a http server without using sockets?
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Mar 31, 2011
Iam using socket programming in one of my problem. The scenario is like this.
=>one module is working as a socket server(process p1) is able to handle client sockets on that port.
=>one module is working as socket client (process p2) is connected to server socket and Tx/Rx data on this socket. This module has some more threads, based on received data from server socket it will connect to http on other thread and get information...
=>one more module is working as socket client (process p3) is also connected to server socket and doing some other transactions.
Here my problem is when in presence of p2, p3 http connection taking more time than the expected. If we wont start p3(means only one server-client socket) then http connection is fast enough.
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Apr 15, 2009
constructing a protocol where in it involves sending and receiving different files, so sending data over consists of file name, size of the file and content of the file, so while receiving can i use functions like strchr() to differentiate these fields for sockets? so to allocate memory for file to save i need to have its size.
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Oct 1, 2010
I have a bash script with a line like this in it:
Code: mysqldump -uusername -ppassword --master-data=2 --single-transaction --quick --add-drop-table --add-drop-database somedatabase | gzip > ./somedatabase.sql.gz The problem is, I have about 16 databases I'm dumping like this, but it's dumping
[Code]....
So, does putting in a & after a command work in a bash script at all? The thought was, if I want to run them in parallel, should I do this?
Code: #!/bin/bash
./scripts/dumpthis &
./scripts/dumpthat &
./scripts/dumpsomemore & Where "dumpthis" is just the first snippet of code above.
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Nov 27, 2010
I use an application called redbutton-browser to access some of the things available on the redbutton digital tv channels. It compiles fine if I use a simple make but fails if I try to run parallel jobs with make -j4. I'd like some help altering the Makefile so that it does a few commands sequentially before it does the rest of the Makefile in parallel.
The relevant bit of the Makefile looks like this:
Code:
ISO13522-MHEG-5.c:xsd2c.c ISO13522-MHEG-5.xsd add_instance_vars.conf add_rtti.conf
make xsd2c
./xsd2c ISO13522-MHEG-5.xsd
./add_instance_vars ISO13522-MHEG-5.c ISO13522-MHEG-5.h
./add_rtti ISO13522-MHEG-5.c > rtti.h
[Code]....
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May 29, 2011
i want to know whether we can write a shell script which can utilize 2 CPU's of a cluster...I heard its possible through C Shell [URL] But im familiar with bourne shell only....So is there a possibility to write Parallel Scripts.
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Mar 18, 2010
I need to spawn 2 processes in parallel and each takes an hour or so to finish. Is the following one of the correct ways of using `at` in a script run by crontab?
Code:
#!/bin/bash
# define the env var, cd, etc... assume everything ok up to this point
date +"The start time is %H:%M:%S"
rm -f a.fin
at now <<END_OF_AT
do_a &> a.log
[Code]....
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Jul 29, 2011
I came across some problems. I need to conduct parallel computing on CUDA. I input "uname -a"and read these: "Linux BXSJC 2.6.38.8-35.fc15.i686 #1 SMP Wed Jul 6 14:46:26 UTC 2011 i686 i686 i386 GNU/Linux". I use CUDAtoolkit 4.0. when I input: cd /home/bxsjc NVIDIA_GPU_Computing_SDK/C and "make -i ",the computer returns
[Code]...
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Aug 8, 2010
I have a little hardware project and I would like to use the parallel port. I basically want to display status code on top of other custom peripheral on an headless server. I only use output as the display (7 segment) is not part of the device itself. The problem is, the parallel port only have 8 standard I/O pins. I have read somewhere that there is a way to change the mode of the port to enable more data pins using a specification not backward compatible with the "classic" mode (so not enabled by default). I didn't find any other information about this. As I would like to have all 17 non-ground pin to avoid using more circuitry than necessary, how to turn this mode on?
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Jul 22, 2014
I am trying to replicate what is happening on this page under the tcsh shell, but using the bash shell found in Wheezy. Here is the page I am referring to:[URL] The command I am trying to replicate is on page 6 under figure 2.4. The command is "prompt> ./mem &; ./mem &".
I would like to run the same program twice, concurrently, but do not know how. Note that I am not trying to use a bash script, but rather by simply using syntax on the command line.
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Sep 3, 2010
I'm looking for a way in Perl to be able to take a list of servers, ssh multiple commands to it and store the results. If I do this process serially, sometimes one server will hang the whole script and if it doesn't, it still takes hours to complete.
I'm thinking what I need to do is make a parent loop that calls out a separate process that passes the server name to the child sub process and then executes all the commands I have defined in its own process. If one server 'hangs', at least that won't stop the script from doing all the other servers in the list.
I'm guessing using the fork() command would serve me best, however, all the online descriptions I have found have been vague at best.
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Oct 15, 2010
Never done it before, don't know how but its due next week. I am a computer systems student and have been required to built a hardware that will be operated by a program in G++ through the parallel ports. The hardware, thats a piece of cake, the software, now that's were the real problem is. I don't even know were to start.
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Apr 29, 2011
I have a script which basically does many tasks and most of them can run in parallel. The server it runs on has 4 cores, so I changed parts of it to a makefile, and then run them with "make -j 4" which helps a lot. But looking at "top" while it runs, I see it could be improved. Sometimes tasks wait for other servers, so a higher -j value would help. And sometimes multiple tasks are waiting on the same disk, then I think a lower -j value would be better.
The kernel is fairly good at sharing CPU time among the cores, but resources like memory and disks are not shared very well. As an experiment, I tried compiling the kernel with "make -j" with no number. It didn't go very well.
So I wondered if anybody know of a better tool for things like this. I think it should be possible to write something that could change the -j value while it runs.For example:
- Start as many tasks in the background as there are cores. When tasks finish, start another one until done.
- After a little while, check CPU and memory usage to decide if more tasks could run in parallel. Or maybe less?
- If different tasks iowait a lot, check if they wait on the same disk. If so, renice/ionice/suspend some of them. In these situations I think it's better to have them run one after another.
- Other ideas?
I thought of making a script like that, but I doubt I'm the first one with that problem. Also, there are probably lots of things I haven't thought of.
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