# 使用 pthread 的 echo server (有bug! why?)

Author: WhoAmI
Date: 20230523
email:[e-mail]
Copyright: CC BY-NC-SA


**《荀子‧勸學》不積跬步，無以至千里；不積小流，無以成江海。**

**I. Mutex variables MUST be declared with type pthread_mutex_t, and must be initialized before they can be used.**
II. 了解 pthread_mutex_lock / pthread_mutex_unlock 與可能問題和代價
III. 程式執行效率與startvation 等問題

[POSIX thread (pthread) libraries](https://www.yolinux.com/TUTORIALS/LinuxTutorialPosixThreads.html)





[Multithreaded Programming (POSIX pthreads Tutorial)](https://randu.org/tutorials/threads/)

這是一個使用pthread 的簡單 echo server!
請用 putty 測試, 您可能測試正常! **但是事實上 有 BUG!!!**

**但是這是有問題的server! 不穩定! 當您連線的 client 很快時就可能會出錯! Why?**

**HINT:** //Get Client's FD 可能出問題! Why? 如何修改?

因此server 的網路程式必須更僅慎! 如有必要需壓力測試!
[pthread_create - create a new thread](https://man7.org/linux/man-pages/man3/pthread_create.3.html)

int pthread_create(pthread_t *restrict thread,
const pthread_attr_t *restrict attr,
void *(*start_routine)(void *),
void *restrict arg);
:::info
Compile and link with -pthread.
特別小心 void *restrict arg
:::
[pthread_join - join with a terminated thread](https://man7.org/linux/man-pages/man3/pthread_join.3.html)

[pthread_detach - detach a thread](https://man7.org/linux/man-pages/man3/pthread_detach.3.html)

[ pthread_exit - terminate calling thread](https://man7.org/linux/man-pages/man3/pthread_exit.3.html)

int pthread_mutex_init(pthread_mutex_t *restrict mutex,
const pthread_mutexattr_t *restrict attr);
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

int pthread_mutex_lock(pthread_mutex_t *mutex);

int pthread_mutex_unlock(pthread_mutex_t *mutex);

**注意 有 BUG!!!!**
請找出來, 還有何時可能有問題? 如何修改?

Hint: malloc

//BUG! simple TCP server
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <resolv.h>
#include <arpa/inet.h>
#include <pthread.h>
void PANIC(char* msg);
#define PANIC(msg) { perror(msg); exit(EXIT_FAILURE); }
#define SERVER_PORT 22222

void* ServerThread(void* arg)
{
    char buf[100];
    int bytes_read;
    int fd = *(int *)arg; //Get Client's FD
    for(;;)
    {
        bytes_read = recv(fd, buf, sizeof(buf), 0);
        send(fd, buf, bytes_read, 0);
        if(strncmp(buf, "q", 1)==0)break;
    }
    printf("Connection Close!\n");
    close(fd);
    return arg;
}

int main(void)
{
    int fd;
    struct sockaddr_in server_addr;
    pthread_t my_thread;
    int client_fd, addr_size;
    if ( (fd= socket(PF_INET, SOCK_STREAM, 0)) < 0 )
        PANIC("Socket");
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(SERVER_PORT);
    server_addr.sin_addr.s_addr = INADDR_ANY;
    if ( bind(fd, (struct sockaddr *)&server_addr, sizeof(server_addr))!= 0 )PANIC("bind");
    if ( listen(fd, 20)!=0 )PANIC("listen");
    for(;;)
    {
        addr_size = sizeof(server_addr);
        client_fd = accept(fd, (struct sockaddr *)&server_addr, &addr_size);
        printf("Connected: %s:%d\n", inet_ntoa(server_addr.sin_addr), ntohs(server_addr.sin_port));
        if ( pthread_create(&my_thread, NULL, ServerThread, &client_fd) != 0 )   //unstable!  FIXIT!
            perror("Thread creation");
        else
            pthread_detach(my_thread);
    }
    exit(0);
}

修正 上面的 bug
請自行 補上
setsockopt SO_REUSEADDR 的處理
與 SIGPIPE signal 的處理

#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <resolv.h>
#include <arpa/inet.h>
#include <pthread.h>
void PANIC(char* msg);
#define PANIC(msg) { perror(msg); exit(EXIT_FAILURE); }
#define SERVER_PORT 22222

void* ServerThread(void* arg)
{
    char buf[256];
    int bytes_read;
    int *fd = (int *)arg; //Get Client's FD

    printf("Client %d\n",*fd);

    for(;;)
    {
        bytes_read = recv(*fd, buf, sizeof(buf)-1, 0);

        if(bytes_read<=0)break;
        buf[bytes_read]=0;

        printf("read: %d bytes:%s\n", bytes_read, buf);
        send(*fd, buf, bytes_read, 0);
        if(strncmp(buf, "q", 1)==0)break;
    }
    printf("Connection Close!\n");
    close(*fd);
    free(fd);
    
    return arg;
}

int main(void)
{
    int fd;
    struct sockaddr_in server_addr;
    pthread_t my_thread;
    int *client_fd, addr_size;
    if ( (fd= socket(PF_INET, SOCK_STREAM, 0)) < 0 )
        PANIC("Socket");
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(SERVER_PORT);
    server_addr.sin_addr.s_addr = INADDR_ANY;
    if ( bind(fd, (struct sockaddr *)&server_addr, sizeof(server_addr))!= 0 )PANIC("bind");
    if ( listen(fd, 20)!=0 )PANIC("listen");
    for(;;)
    {
        addr_size = sizeof(server_addr);
        client_fd = malloc(sizeof (int));
        *client_fd = accept(fd, (struct sockaddr *)&server_addr, &addr_size);
        
        printf("Connected: %s:%d\n", inet_ntoa(server_addr.sin_addr), ntohs(server_addr.sin_port));
        if ( pthread_create(&my_thread, NULL, ServerThread, client_fd) != 0 )   //unstable!  FIXIT!
            perror("Thread creation");
        else
            pthread_detach(my_thread);
    }
    exit(0);
}

#define LONGSTRING(...) #__VA_ARGS__

簡單 pthread 版 web server

/*
 *Author: WhoAmI
 *Date: 20230523
 *
 */

//Simple HTTP server
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <resolv.h>
#include <arpa/inet.h>
#include <pthread.h>
void PANIC(char* msg);
#define PANIC(msg) { perror(msg); exit(EXIT_FAILURE); }
#define SERVER_PORT 22222
#define INFO(EXP) \
do { if (EXP) \
        fprintf (stderr, "Warning: " #EXP "=%d\n",EXP); } \
while (0)

#define LONGSTRING(...) #__VA_ARGS__

const char  *indexhtml2=LONGSTRING(HTTP/1.1 200 OK\nContent-Type: text/html;  charset=UTF-8\r\n\r\n<html><body>Welcome</body>
</html>);

const char *indexhtml = LONGSTRING(HTTP/1.1 200 OK\nContent-Type: text/html;  charset=UTF-8\r\n\r\n
<!DOCTYPE html>
<html>
<style>
table, th, td {
  border:1px solid black;
}
</style>
<body>

<h2>A basic HTML table</h2>

<table style="width:100%">
  <tr>
    <th>Company</th>
    <th>Contact</th>
    <th>Name</th>
  </tr>
  <tr>
    <td>John </td>
    <td>Maria</td>
    <td>Joe</td>
  </tr>
  <tr>
    <td>FoodPanda</td>
    <td>Chang</td>
    <td>Beer</td>
  </tr>
</table>

<p>we have added borders to the table.</p>

</body>
</html>

             
);

#define debugx(x) 

static void sig_pipe(int signum)
{
    printf(" Broken Pipe!\n");
}
static void HandleSignal(void){  //handle all signals
   signal(SIGPIPE, sig_pipe);
}
void* ServerThread(void* arg)
{
    char buf[2048];
    int bytes_read;
    int len=0;
    int *fd = (int *)arg; //Get Client's FD

    printf("Client %d\n",*fd);

    for(;;)
    {
        bytes_read = read(*fd, buf, sizeof(buf)-1);

        if(bytes_read<=0)break;
        buf[bytes_read]=0;
        INFO(bytes_read);
        
        len=strlen(indexhtml);
        debugx(printf("read: %d bytes:\n%s\n", bytes_read, buf));
        
        write(*fd, indexhtml, len+1);
        debugx(printf("%s",indexhtml));
        
        if(strncmp(buf, "q", 1)==0)break;
        
        break;
    }
    printf("Connection Close!\n");
    close(*fd);
    free(fd);
    
    return arg;
}

int main(void)
{
    int fd;
    struct sockaddr_in server_addr;
    int yes=1;
    pthread_t my_thread;
    int *client_fd, addr_size;
    
    
    HandleSignal();
    if ( (fd= socket(PF_INET, SOCK_STREAM, 0)) < 0 )
        PANIC("Socket");
    if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) PANIC("setsockopt");
  
        
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(SERVER_PORT);
    server_addr.sin_addr.s_addr = INADDR_ANY;
    if ( bind(fd, (struct sockaddr *)&server_addr, sizeof(server_addr))!= 0 )PANIC("bind");
    if ( listen(fd, 20)!=0 )PANIC("listen");
    for(;;)
    {
        addr_size = sizeof(server_addr);
        client_fd = malloc(sizeof (int));
        printf("Waiting\n");
        *client_fd = accept(fd, (struct sockaddr *)&server_addr, &addr_size);
        
        printf("Connected: %s:%d\n", inet_ntoa(server_addr.sin_addr), ntohs(server_addr.sin_port));
        if ( pthread_create(&my_thread, NULL, ServerThread, client_fd) != 0 )   //unstable!  FIXIT!
            perror("Thread creation");
        else
            pthread_detach(my_thread);
    }
    exit(0);
}

:::info

Futher Reading:

[Pthread Scheduling, Fairness, Power, Performance](https://hackmd.io/@pingulinux/Pthread-Scheduling-Fairness-Power)

[Circular Buffer](https://hackmd.io/@pingulinux/CircularBuffer)

:::


HW. double linked list (不考慮排序), thread 2,3 write new data, thread1 read and delete data, 您如何設計?