I understand asynchronous and synchronous, whether it is blocking or not, but I just don’t understand how openresty implements asynchronous non-blocking IO and achieves high concurrency processing capabilities? I usually write Lua interfaces, but I can see considerable QPS when doing stress tests, but it feels no different from the running process of http API written in other languages (such as PHP interface). Can any hero use an example to briefly explain its implementation on asynchronous non-blocking, and compare it with the PHP interface why PHP cannot implement it.