This change removes a bottleneck at the client/server protocol level for high concurrency workloads.
When reading a packet from a socket, the read can be performed either in non-blocking mode or in blocking mode. The non-blocking mode was originally chosen because it avoids the cost of setting up an alarm in case of a timeout: thus the first attempt to read is done in non-blocking mode, and only if it fails, the next attempts are done in blocking mode.
However, this behavior can hurt performance as the switch from non-blocking mode to blocking mode is expensive, requiring calls to the fcntl function and calls into the kernel.
The solution is to use socket timeouts, with the
SO_SNDTIMEO options. This way, the timeouts are automatically handled by the operating system, which means that all reads can be done in blocking mode.
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