# Question about sockets/listeners

**URL:** <https://www.ruby-forum.com/t/question-about-sockets-listeners/123257>\
**Category:** Ruby\
**Created:** [December 15, 2007, 3:38pm UTC](https://www.ruby-forum.com/t/question-about-sockets-listeners/123257 "2007-12-15T15:38:31Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![ratcheer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/aca169/32.png) [@ratcheer](https://www.ruby-forum.com/u/ratcheer)\
**Post date:** [December 15, 2007, 3:38pm UTC](https://www.ruby-forum.com/t/question-about-sockets-listeners/123257/1 "2007-12-15T15:38:31Z")

</div>

hi, i’m very new to ruby and so i’d be very grateful of any help on  
this. I am writing a script that listens for UDP packets on a  
particular port. This is very easy using ‘socket’. I then want to make  
a script that simulates lots of clients sending UDP packets to the  
listener. These clients should send a UDP packet from a particular port  
and then listen for a response on that same port. For this reason, I am  
trying to run each simulated client in a different thread. A simplified  
version of what i have done so far is shown below, however, when I run  
this, the client stops sending packets after the 66th one. Can someone  
explain this to me please? why is it stopping at 66? which limit am i  
hitting?

Also, any suggestions on how to improve the code will be gratefully  
received. Thanks

#### Listener.rb

require “socket”

socket = UDPSocket.open  
socket.bind("",1500)

while true  
message, details = socket.recvfrom(512)  
p message  
end

#### Clients.rb

require ‘socket’

SERVER\_IP = “127.0.0.1”  
SERVER\_PORT = 1500

packets=[]  
threads =[]

# Build an array of packets

for i in 1…100  
packets \<\< “packet#{i}”  
end

# For Packet to be sent, start a new thread

for packets\_to\_send in packets  
sleep 0.1  
threads \<\< Thread.new(packets\_to\_send) do |packet|

#Generate a random port  
port = rand(60000)

# Open a socket on that port

socket = UDPSocket.open  
socket.bind("",port)

# Send the packet

puts “Sending #{packet}”  
socket.send(packet, 0, SERVER\_IP, SERVER\_PORT)

while true  
message, message\_details = socket.recvfrom(512)  
end

end  
end

---

<div class="post-metadata">

**Author:** ![ratcheer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/aca169/32.png) [@ratcheer](https://www.ruby-forum.com/u/ratcheer)\
**Post date:** [December 15, 2007, 4:50pm UTC](https://www.ruby-forum.com/t/question-about-sockets-listeners/123257/2 "2007-12-15T16:50:17Z")

</div>

On Dec 15, 2007, at 9:38 AM, James C. wrote:

> A simplified  
> version of what i have done so far is shown below, however, when I run  
> this, the client stops sending packets after the 66th one. Can  
> someone  
> explain this to me please? why is it stopping at 66? which limit  
> am i  
> hitting?

My first guess is that you are running out of file descriptors. It  
looks like each thread creates a new socket, calls send, then calls  
recvfrom repeatedly, never closing the socket and freeing the file  
descriptor.

You should close the socket after receiving a response. Alternatively  
you could see how to raise the per/process file descriptor limit for  
your system (for bash, try looking at the ulimit command–the exact  
command and syntax depends on the shell you are using).

Gary W.

---

<div class="post-metadata">

**Author:** ![ratcheer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/aca169/32.png) [@ratcheer](https://www.ruby-forum.com/u/ratcheer)\
**Post date:** [December 15, 2007, 4:56pm UTC](https://www.ruby-forum.com/t/question-about-sockets-listeners/123257/3 "2007-12-15T16:56:44Z")

</div>

On Dec 15, 2007, at 9:38 AM, James C. wrote:

> why is it stopping at 66? which limit am i  
> hitting?

You main thread may be existing before all the  
threads have been started.

After creating all the threads you need to wait  
for them to finish by calling t.join on each one.

Gary W.

---

<div class="post-metadata">

**Author:** ![ratcheer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/aca169/32.png) [@ratcheer](https://www.ruby-forum.com/u/ratcheer)\
**Post date:** [December 15, 2007, 5:19pm UTC](https://www.ruby-forum.com/t/question-about-sockets-listeners/123257/4 "2007-12-15T17:19:44Z")

</div>

Gary W. wrote:

> You should close the socket after receiving a response.

Sorry, I should have said, I am expecting mulitple responses from the  
server and hence I want to keep the socket open.

Gary W. wrote:

> You main thread may be existing before all the threads have been started.

The threads shouldn’t be exiting because I have the ‘while true’ in  
there. I have just tried joining the threads and it didn’t fix it. It  
might be the file descriptor thing, i’ll have to have a read up about  
it. Thanks

---

<div class="post-metadata">

**Author:** ![ratcheer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/aca169/32.png) [@ratcheer](https://www.ruby-forum.com/u/ratcheer)\
**Post date:** [December 15, 2007, 5:38pm UTC](https://www.ruby-forum.com/t/question-about-sockets-listeners/123257/5 "2007-12-15T17:38:58Z")

</div>

On Dec 15, 2007 9:38 AM, James C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> hitting?
> 
> Also, any suggestions on how to improve the code will be gratefully  
> received. Thanks

Using a nonthreaded approach, I got up to about 360 packets through on a  
single run. (This program requires the Ruby/EventMachine library):

#-----------------------------------------  
require ‘rubygems’  
require ‘eventmachine’

EM.epoll

SERVER = “127.0.0.1”  
PORT = 1500

module Server  
def receive\_data data  
send\_data “I saw your #{data}”  
end  
end

module Client  
def post\_init  
@@counter ||= 0  
@@counter += 1  
send\_datagram “Data packet #{@@counter}”, SERVER, PORT  
end  
def receive\_data data  
@@received ||= 0  
@@received += 1  
p “Received #{@@received}: #{data}”  
end  
end

EM.run {  
EM.open\_datagram\_socket SERVER, PORT, Server  
(60000…60400).each {|n|  
EM.open\_datagram\_socket SERVER, n, Client  
}  
}

#-------------------------------

I did two things differently: first, I didn’t introduce a delay between  
each  
new socket. If I had, then this program would probably have scaled much  
farther. And second, I used sequential port numbers rather than random  
ones,  
to avoid trying to open an already-open port, and to avoid trying to  
open a  
privileged one.

---

<div class="post-metadata">

**Author:** ![ratcheer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/aca169/32.png) [@ratcheer](https://www.ruby-forum.com/u/ratcheer)\
**Post date:** [December 15, 2007, 6:17pm UTC](https://www.ruby-forum.com/t/question-about-sockets-listeners/123257/6 "2007-12-15T18:17:40Z")

</div>

On Dec 15, 2007 9:38 AM, James C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> hitting?

Ok, I tweaked my test program somewhat:

#---------------------------------------  
require ‘rubygems’  
require ‘eventmachine’

EM.epoll

SERVER = “127.0.0.1”  
PORT = 1500

module Server  
def receive\_data data  
send\_data “I saw your #{data}”  
end  
end

module Client  
def post\_init  
@@counter ||= 0  
@@counter += 1  
send\_datagram “Data packet #{@@counter}”, SERVER, PORT  
end  
def receive\_data data  
@@received ||= 0  
@@received += 1  
p “Received #{@@received}: #{data}”  
close\_connection  
end  
end

EM.run {  
EM.open\_datagram\_socket SERVER, PORT, Server

```
    t = EM::PeriodicTimer.new(0.05) {
            n = rand(1000) + 60000
            EM.open_datagram_socket SERVER, n, Client
    }

```

}

#-----------------------------

Now I’m delaying before opening each client as you were, and I’m using  
random ports chosen in a high range. I’m also closing client sockets  
after  
they receive their responses. This version is now up to 10,000 packets  
and  
it’s still running strong.

Also, on a Linux kernel, I took out the close\_connection statement and  
used  
EPOLL to eliminate Ruby’s limit of 1024 descriptors per process. I had  
to  
add a mechanism to keep the random port number generator from giving the  
number of an already-open port. That program is also still running at  
well  
over 10,000 open sockets and packets now.