IO Event

include: co/co.h.


enum _ev_t {
     ev_read = 1,
     ev_write = 2,
  • Type of I/O event.


co::io_event is used to convert non-blocking I/O to synchronous mode. The user performs I/O operations on a non-blocking socket in coroutine. When the socket is unreadable or unwritable, the user calls the wait() method of co::io_event to suspend the coroutine and wait for the I/O event; When the socket becomes readable or writable, the scheduling thread will wake up the coroutine again and continue the I/O operation.


1. io_event(sock_t fd, _ev_t ev);
2. io_event(sock_t fd, int n=0); // for windows only
  • 1, parameter fd is a non-blocking socket, parameter ev is ev_read or ev_write. Calling the wait() method will wait for the I/O event specified by ev on the socket. When wait() returns successfully, the user needs to call recv, send or other API to complete the I/O operation. On windows, fd must be a TCP socket (for UDP, it is difficult to simulate the behavior of epoll or kqueue with IOCP).
  • 2, for windows only. fd can be a UDP socket, but users need to manually call WSARecvFrom, WSASendTo or other API to send overlapped I/O requests to IOCP, and then call the wait() method, when wait() returns successfully, it means that IOCP has completed the I/O operation. The specific usage is not detailed here. There are detailed comments in the code. It is recommended to refer directly to the source code of co::io_event, and the implementation of co::accept, co::connect, co::recvfrom, co::sendto on windows.


  • Removes previously registered I/O events from epoll or kqueue.


bool wait(uint32 ms=-1);
  • This method waits for the I/O event on the socket. The parameter ms is the timeout in milliseconds. The default is -1 and never times out.
  • This method blocks until the I/O event arrives, or times out or an error occurs.
  • This method returns true on success, false on timeout or error.

#Code Example

int recv(sock_t fd, void* buf, int n, int ms) {
     const auto sched = xx::gSched;
     CHECK(sched) << "must be called in coroutine..";

     co::io_event ev(fd, ev_read);
     do {
         int r = (int) __sys_api(recv)(fd, buf, n, 0);
         if (r != -1) return r;

         if (errno == EWOULDBLOCK || errno == EAGAIN) {
             if (!ev.wait(ms)) return -1;
         } else if (errno != EINTR) {
             return -1;
     } while (true);