问当响应是异步时，如何在Node.js中处理多个同时请求？

EN

int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, time *timeout);

// Pseudocode:

// Say you just sent a request to a mysql database and also sent a http
// request to google maps. You are waiting for data to come from both.
// Instead of calling `read()` which would block the thread you add
// the sockets to the read set:

add mysql_socket to readfds
add maps_socket to readfds

// Now you have nothing else to do so you are free to wait for network
// I/O. Great, call select:

select(2, &readfds, NULL, NULL, NULL);

// Select is a blocking call. Yes, non-blocking I/O involves calling a
// blocking function. Yes it sounds ironic but the main difference is
// that we are not blocking waiting for each individual I/O activity,
// we are waiting for ALL of them

// At some point select returns. This is where we check which request
// matches the response:

check readfds if mysql_socket is set {
    then call mysql_handler_callback()
}

check readfds if maps_socket is set {
    then call maps_handler_callback()
}

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