How to use IOCP on windows, and implement multi-client server with C++

In the Windows system, you can use IOCP(Input/Output Completion Ports) to achieve high-performance I/O multiplexing mechanism. IOCPIt is an efficient asynchronous I/O mechanism in the Windows system, which can be used to implement high-concurrency network servers. The following are IOCPthe basic steps to use to implement a multi-client server:

1. create socket

socketCreate a TCP server socket using a function, for example:

#include <winsock2.h>

WSADATA wsaData;
WSAStartup(MAKEWORD(2, 2), &wsaData);

SOCKET server_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
struct sockaddr_in server_address;
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = INADDR_ANY;
server_address.sin_port = htons(8888);
bind(server_socket, (struct sockaddr*)&server_address, sizeof(server_address));
listen(server_socket, 10);

1. Create an IOCP object

Use CreateIoCompletionPortthe function to create an IOCP object and associate the server socket with the IOCP object, for example:

HANDLE iocp = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 0);
CreateIoCompletionPort((HANDLE)server_socket, iocp, 0, 0);

1. Handle connection requests

Use AcceptExa function to monitor client connection requests, and associate a new client socket with an IOCP object, for example:

LPFN_ACCEPTEX AcceptExFunc;
GUID GuidAcceptEx = WSAID_ACCEPTEX;
DWORD dwBytes = 0;
WSAIoctl(server_socket, SIO_GET_EXTENSION_FUNCTION_POINTER, &GuidAcceptEx, sizeof(GuidAcceptEx), &AcceptExFunc, sizeof(AcceptExFunc), &dwBytes, NULL, NULL);

SOCKET client_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
int address_length = sizeof(struct sockaddr_in);
char accept_buffer[2 * (sizeof(struct sockaddr_in) + 16)];
AcceptExFunc(server_socket, client_socket, accept_buffer, 0, sizeof(struct sockaddr_in) + 16, sizeof(struct sockaddr_in) + 16, NULL, NULL);
CreateIoCompletionPort((HANDLE)client_socket, iocp, (ULONG_PTR)client_socket, 0);

1. Handle I/O completion events

Use GetQueuedCompletionStatusfunctions to get I/O completion events and handle read and write operations, for example:

while (true) {
    DWORD bytes_transferred = 0;
    ULONG_PTR completion_key = 0;
    LPOVERLAPPED overlapped = NULL;
    GetQueuedCompletionStatus(iocp, &bytes_transferred, &completion_key, &overlapped, INFINITE);

    if (bytes_transferred == 0) {
        closesocket((SOCKET)completion_key);
        printf("Client disconnected\n");
        continue;
    }

    SOCKET client_socket = (SOCKET)completion_key;
    if (overlapped == NULL) {
        char buffer[1024] = {0};
        recv(client_socket, buffer, bytes_transferred, 0);
        printf("Received data: %s\n", buffer);
    } else {
        WSABUF buffer;
        buffer.buf = new char[1024];
        buffer.len = 1024;
        DWORD flags = 0;
        WSARecv(client_socket, &buffer, 1, NULL, &flags, overlapped, NULL);
    }
}

1. send data

Use the client socket to send data, for example:

char* data = "Hello, world!";
send(client_socket, data, strlen(data), 0);

The above are IOCPthe basic steps for implementing a multi-client server. It should be noted that IOCPthe code is relatively complex, and it is necessary to understand concepts such as asynchronous I/O and event-driven programming.