网络服务器-Loopback (Internet Sockets) VS UNIX Domain Sockets

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本文探讨了在本机进程间通信中，TCP Loopback（Internet Sockets）与UNIX Domain Sockets的性能差异。尽管TCP Loopback在本机通信上涉及更多操作，如封包/解包和校验，但在资源消耗方面仍较低。然而，对于高并发短连接场景，TIME_WAIT状态在TCP中可能成为问题，此时UNIX Domain Sockets展现出优势。文中提供了简单的性能测试结果，并附带了测试代码。

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在本机的进程间通信中，TCP和UNIX域套接字是两种比较简单方便的通信方式，TCP基本以回路地址形式表现，回路地址在本机通信上还是要比UNIX域套接字多了封包/解包/校验和/序列确认等操作

那么对于这两种方式的性能比较可以参考以下文章：

http://bhavin.directi.com/unix-domain-sockets-vs-tcp-sockets/

http://lists.freebsd.org/pipermail/freebsd-performance/2005-February/001143.html

同时做了一个简单的对比测试，虚拟机上（1CPU、256M内存），单进程server、client，10w次5字节echo server结果（进行多次，差不多平均结果，系统其它参数未观察）：

回路地址：
real    0m5.879s
user    0m0.012s
sys     0m2.763s
 
UNIX域套接字：
real    0m11.433s
user    0m0.019s
sys     0m4.641s

其实网络协议处理主要消耗CPU资源，但相对来说资源消耗还是比较低的，不过对于要求非常高的短连接网络并发处理，TIME_WAIT对于回路地址是个问题，这点UNIX域套接字非常有优势。

以下为测试代码：

1. unix域套接字server

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/un.h>

#undef  offsetof
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

int main(int argc, char *argv[])
{
    int sock = 0;
    int conn = 0;
    socklen_t addrlen = 0;
    struct sockaddr_un addr;
    char buf[64] = {0};

    unlink("foo.socket");

    if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
        printf("socket failed\n");
        return -1;
    }

    addr.sun_family = AF_UNIX;
    strcpy(addr.sun_path, "foo.socket");

    addrlen = offsetof(struct sockaddr_un, sun_path) + strlen(addr.sun_path);
    if (bind(sock, (struct sockaddr *)&addr, addrlen) < 0) {
        printf("bind failed\n");
        return -1;
    }

    printf("UNIX domain socket bound\n");

    if (listen(sock, 128) < 0) {
        printf("listen failed\n");
        return -1;
    }

    while (1) {
        if ((conn = accept(sock, (struct sockaddr *)NULL, NULL)) < 0) {
            printf("accept connect failed\n");
            continue;
        }

        if (readn(conn, buf, 5) < 0) {
            printf("read msg failed\n");
            return -1;
        }
        buf[5] = '\0';

        //printf("readn: %s\n", buf);

        if (write(conn, buf, strlen(buf)) < 0) {
            printf("write msg failed\n");
            return -1;
        }

        close(conn);
    }

    close(sock);
    return 0;
}

2. unix域套接字client

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/un.h>

#undef  offsetof
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

int main(int argc, char *argv[])
{
    int i = 0;
    int sock = 0;
    socklen_t addrlen;
    struct sockaddr_un addr;
    char buf[64] = {0};

    while (i++ < 100000) {
        if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
            printf("socket failed\n");
            return -1;
        }

        addr.sun_family = AF_UNIX;
        strcpy(addr.sun_path, "foo.socket");

        addrlen = offsetof(struct sockaddr_un, sun_path) + strlen(addr.sun_path);

        if (connect(sock, (struct sockaddr *)&addr, addrlen) < 0) {
            printf("connet failed\n");
            return -1;
        }

        if (write(sock, "helo\n", 5) < 0) {
            printf("write msg failed\n");
            return -1;
        }

        if (readn(sock, buf, 5) < 0) {
            printf("read msg failed\n");
            return -1;
        }
        buf[5] = '\0';

        //printf("readn: %s", buf);

        close(sock);
    }

    return 0;
}

3. socket套接字server

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

int main(int argc, char** argv)
{
    int on = 1;
    int sock = 0;
    int conn = 0;
    struct sockaddr_in addr;
    char buf[64];

    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        printf("socket failed\n");
        return -1;
    }

    setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));

    memset(&addr, 0, sizeof(addr));

    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    addr.sin_port = htons(6666);

    if (bind(sock, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
        printf("bind failed\n");
        return -1;
    }

    if (listen(sock, 128) < 0) {
        printf("listen failed\n");
        return -1;
    }

    while (1) {
        if ((conn = accept(sock, (struct sockaddr *)NULL, NULL)) < 0) {
            printf("accept connect failed\n");
            continue;
        }

        if (readn(conn, buf, 5) < 0) {
            printf("read msg failed\n");
            return -1;
        }
        buf[5] = '\0';

        //printf("readn: %s", buf);

        if (write(conn, buf, strlen(buf)) < 0) {
            printf("write msg failed\n");
            return -1;
        }

        close(conn);
    }

    close(sock);
    return 0;
}

4. socket套接字client

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
    int i = 0;
    int sock = 0;
    struct sockaddr_in addr;
    char buf[64] = {0};

    while (i++ < 100000) {
        if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
            printf("socket failed\n");
            return -1;
        }

        memset(&addr, 0, sizeof(addr));

        addr.sin_family = AF_INET;
        addr.sin_port = htons(6666);
        addr.sin_addr.s_addr = inet_addr("127.0.0.1");

        if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
            printf("connect failed\n");
            return -1;
        }

        if (write(sock, "helo\n", 5) < 0) {
            printf("write msg failed\n");
            return -1;
        }

        if (readn(sock, buf, 5) < 0) {
            printf("read msg failed\n");
            return -1;
        }
        buf[5] = '\0';

        //printf("reand: %s", buf);

        close(sock);
    }

    return 0;
}

5. 读数据共用函数

int readn(int fd, char *buf, int buflen)
{
    int nleft = 0;
    int nread = 0;
    char *ptr = NULL;

    ptr = buf;
    nleft = buflen;

    while (nleft > 0) {
        if ((nread = read(fd, ptr, nleft)) < 0) {
            if (EINTR == errno) {
                nread = 0;
            }
            else {
                return -1;
            }
        }
        else if (0 == nread) {
            break;
        }

        nleft -= nread;
        ptr += nread;
    }

    return buflen - nleft;
}