If someone has told you synchronous I&#x2F;O is slow, they&#x27;ve obviously misunderstood the entire C10k argument going on for a while.<p>The problem with synchronous I&#x2F;O is not speed, but blocking. Blocking means the only possible concurrency model is based on processes or threads. Consequentially, most performance problems with synchronous I&#x2F;O stem from the thread model: context switching, synchronization, memory overhead, thread-pool starvation and so on.