CODEWITHSUNDEEP
c++linuxsocketstcp
erin c
erin c

Reputation: 1345

Interminent Delays in C++ Tcp Communication in Linux

I have a device which sends data every 20 milliseconds over TCP. I have an application which connects to this device, starts the socket communication. My Application listens on a seperate thread and reads the data as fast as data is ready, puts data aside, and some other thread processes it. Device is directly connected to the computer via ethernet cable.

I see a strange problem and I am trying to understand the reason why, Almost once in every minute, it takes approximately 50 milliseconds to receive a packet from the device. I do a blocking read which will try reading for a second, and will finish as fast as data is ready, normally it takes approximately 20 ms as I would expect, but like I said before there are times it takes 50 ms even though it is very rare(1 in 3000). What I noticed is the packets after late packet arrives immediately, so it makes me think that there's some delay on the network layer. I also examined the timestamps of the packets(which is given by the device), they are consistenly increasing by 20 ms's.

Is it normal to see delays like that when the device is directly connected to the computer, Since it is TCP there might be lots of effort under the hood(CRC checks, out of order packages, retransmissions, etc). I still want to find an alternative way to prevent this delay than accepting the fact that it might happen.

Any insights will be greatly appreciated.

Upvotes: 1

Views: 1348

Answers (1)

inkooboo
inkooboo

Reputation: 2944

It's probably result of Nagle's algorithm which is turned on by default in TCP/IP socket.

Use setsockopt() to set the TCP_NODELAY flag on socket that sends data to turn it off.

Upvotes: 1

Related Questions