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    <p>I doubt this answers your question, but I think it will help.</p> <p>In void SerialManager::asyncRead(byte*, const size_t&amp;, bool&amp;), there are two bugs:</p> <ol> <li><p>You're using the value of errno (and printing messages based on it using perror) when read returns success, not only when it errors out (return value &lt; 0). On success, errno is not specified to have any particular value. So you're effectively using garbage data; the EBUSY you're getting probably doesn't mean anything whatsoever. errno is only defined to have a particular value when a particular error has occurred. See 'man errno' on a Linux system, which on my Debian system says in relevant part: "Its value is significant only when the return value of the call indi‐cated an error (i.e., -1 from most system calls; -1 or NULL from most library functions); a function that succeeds is allowed to change errno.". Note the "is allowed to", rather than "must".</p></li> <li><p>You read into a temp buffer, then copy it byte-by-byte into the destination buffer which the caller passed. This is a pointless waste of CPU cycles and memory bandwidth. You could just read straight into the caller's buffer. Even if you must (for some strange reason) read into a temp buffer then copy it elsewhere, you should copy it elsewhere using memcpy(3) or perhaps memmove(3), not using your own byte-by-byte loop.</p></li> </ol> <p>Regarding the design, I don't understand the point of having multiple readers or writers when there is only one serial port. Are you trying to achieve parallelism? I don't see how you can, with only one serial port. If you want asynchronicity but not parallelism, you should investigate fcntl(fd, F_SETFL, existing_flags &amp; O_ASYNC) (although signals are rather old and ugly), or perhaps just set the fd non-blocking, then call select() in the inner event loop of your application and handle any I/O (if any) that's available.</p> <p>Hope this helps!</p>
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