Hello everyone, I have two inquiries that I'm hoping someone can provide insight on. 1. I came across a suggestion on this forum regarding setting the ReadSocket timeout to 0 to minimize latency and improve the performance of the MSG instruction. This timeout is specifically related to the MSG instruction with the service type of ReadSocket and a designated timeout for the source element. 2. My primary challenge involves resolving issues with a TCP client connection that needs to handle variable length data from a TCP server. Ideally, I would like the client to read data until it reaches a delimiter character, such as a carriage return or line feed ($n$l). However, this task may not be straightforward due to the nature of TCP being a byte-based data stream. Thank you for your assistance!
Q1. Setting the parameter to 0 will allow data to be retrieved without delay. However, it is recommended to use a number equal to the task period for optimal performance, as 0 may not be documented in manuals. Keep in mind that you may frequently encounter an empty buffer. The response to an empty buffer varies between UDP and TCP protocols, and there are TCP response discrepancies between V35 and some EN4TRs that were resolved in V36. Q2. I typically gather all incoming TCP packets into a single large buffer without conditions, and then proceed to parse the buffer separately. In your situation, you will need to search for $n$l. For guidance on this process, consider examining sample applications such as Modbus TCP AOI to observe how it is executed.
Thank you for your input! I believe you mentioned setting the timeout to 0 in a forum post. To avoid relying on the timeout, have you considered setting the buflen to a size smaller than the shortest expected data? You can then append this data to a single large buffer that is cleared only after parsing. This approach can help maintain the efficiency and responsiveness of the communication process.
I am unable to provide an answer as I lack specific details to give guidance. I am not a fan of the concept of allowing Reads to block, holding onto the socket and hindering Writes. Instead, I prefer implementing quick reads without waiting for data. If there is no data available, I move on swiftly. However, if there is data present, I add it to the buffer. This approach has proven to be the most effective for me since 2005 when sockets were first introduced, and I have been utilizing it ever since.
No need to worry! I have been using the Rockwell-provided SKT_AOI_TCP_CLIENT and have noticed some limitations that are impacting my specific application. In my case, I need to write to the socket before reading anything, but the constant execution of the read command by the AOI causes a delay that hinders the responsiveness of my write commands. I truly appreciate your assistance in helping me navigate through this issue.
I remember coming across this All-in-One (AIO) solution, but I never ended up incorporating it into my applications, so I can't provide any feedback on it.
Hello! To your first question, setting the ReadSocket timeout to 0 can indeed reduce the latency in some scenarios, but at the risking of overloading the processor if the messages arrive at a very high frequency. It's about figuring out the balance between efficiency and system safety. As for your second problem, handling variable length data can be tricky with TCP. One strategy is to implement a buffer that accumulates the data until the delimiter character is found. Essentially the client has to keep reading and appending data to your buffer until it detects the delimiter. Remember, each 'read' may retrieve more than one message or only part of a message, so you can't assume each read corresponds to one complete message. I hope this helps!
It's true, the ReadSocket timeout can be set to 0 to reduce latency, but be aware that this potentially makes your system more vulnerable to hang-ups if any network glitches occur - refer to it as a trade-off between speed and stability. For your second issue, you’re correct that TCP is a streaming protocol with no concept of message boundaries. One traditional approach would be to implement a buffer on the client-side that reads data from the server, scanning for your delimiter character. Incoming data gets appended to the buffer and you only process or "consume" that data once you have a complete message, signified by your delimiter. It essentially becomes a 'read until delimiter' function. Remember that TCP might deliver part of your message in one packet and another part in the next, so buffering and scanning are important. However, every application is unique and these suggestions may need tweaking to best fit yours.
Hey there! For your first question, setting the ReadSocket timeout to 0 can indeed help reduce latency, but make sure to monitor how it affects stability, as it might lead to dropped connections if there's a temporary hiccup in the network. As for your TCP client issue, to handle variable length data effectively, consider implementing a loop that reads incoming bytes until your specified delimiter is detected. Using a buffer to accumulate the bytes while checking for your delimiter can be a solid approach. Just remember to manage buffer sizes carefully to avoid overflow issues! Good luck!
Hey there! For your first inquiry about setting the ReadSocket timeout to 0, it can definitely help reduce latency, but just be cautious since it might lead to blocking issues if there's a connectivity problem. As for your TCP client, handling variable length data is tricky since TCP doesn't inherently understand message boundaries. One approach you can take is to implement a protocol on top of TCP that sends the length of the message before the actual data, allowing your client to know when it has received the complete message. Alternatively, using the delimiter method is valid; just make sure to implement error checking in case the data stream is interrupted. Good luck!
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Answer: Answer: Setting the ReadSocket timeout to 0 can help improve the performance of the MSG instruction by reducing latency. This timeout setting is specifically related to the MSG instruction with the service type of ReadSocket and a designated timeout for the source element.
Answer: Answer: Handling variable length data in a TCP client connection can be challenging due to TCP being a byte-based data stream. One approach is to read data until a delimiter character, such as a carriage return or line feed ($n$l), is encountered. However, this task may not be straightforward and may require careful implementation to ensure data integrity and proper handling.
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