I am just very thankful that stackoverflow exists, so many questions that would have taken me hours, they are answred here from exprienced people, thanks everyone :).
One question I have, suppose I am connected to a server via a websocket that sends me data every 1 second, and I am processing that data in a function call it on_feed(cons map_t& m). Suppose each on_feed call takes 2 seconds, what will happend? Is there an internal queue in the OS that will process the input and queue them?
I hope I am clear, if not what happens if a server sends data too quickly that I can't process it as my process takes time. (I don't want to use my own queue :) )
Thanks!!
CodePudding user response：
A websocket is a TCP socket. TCP sockets have an internal buffer of some unspecified size that holds unread data, until it's read from the socket.
When enough unread data accumulates there are low-level IP messages and protocols that get communicated to the sender indicating that the peer cannot accept any more data on the socket (and additional messages when this is no longer the case and the sending can resume).
The sender will also have a buffer that holds some amount of data that was written to the socket but not yet transmitted to the peer, also of some unspecified size; so the sender's socket's buffer will also accumulate some amount of data, and when that buffer is full any ordinary write() to the socket will block until such time that more data to the socket can be written.
At that point what happens depends entirely on the application on the other end of the websocket and it is entirely up to the application to figure out what to do next. It may choose to wait forever, or for some indeterminate period of time until it can write more data to the socket; or it may choose to close the socket immediately, it is entirely up to the websocket server.
CodePudding user response：
Is there an internal queue in the OS that will process the input and queue them?"
Most operating system kernels do not have built-in support for the WebSocket protocol. They generally only provide TCP/IP support. You will probably be using a WebSocket library which will be linked to your program. This library will likely not be part of the operating system (in the narrow sense). In order to support WebSocket messages, this library will probably have its own input queue.
what happens if a server sends data too quickly that I can't process it as my process takes time
If the input queue of the WebSocket library is full, then the WebSocket library will probably stop accepting new data from the server, until more input has been processed and there is room in the queue to accept new input.
Therefore, it should generally not be a problem if a server attempts to send data faster than the client can process.
If the server software is programmed to send new data sets to the client at a certain rate, but the client is unable to process the data sets at this rate, then the client will probably stop accepting new data after some time, due to its input buffer being full. After that, the server's output buffer will start to fill. If the server software is well-designed, then it should be able to handle this situation well, and it will stop generating data once the output buffer is full, until there is room again in the output buffer.
However, if the server software is not well-designed, then, depending on the situtation, it may not be able to cope with this type of problem.
Also, even if the server software is well-designed, it may expect the client to be able to process the WebSocket messages in a timely manner, and may abort the connection if the client is taking too long.