我正在为学校作业实现一个简单的多线程 Web 服务器，并且遇到了用于每个连接的连接文件描述符的一些同步问题。我最初的问题是，一个线程有时会关闭另一个线程中也使用的文件描述符的文件描述符（conn_fd）。当其他线程尝试发送（）或接收（）时，这将导致错误的文件描述符错误。
我的解决方法是存储最多 1000 个的每个文件描述符（我知道是任意数量并且容易出错）当前是否打开。如果accept()返回的文件描述符已经打开，我的程序调用fcntl(conn_fd, F_DUPFD, 0);创建重复的文件描述符，以便一个线程不会无意中关闭另一个线程需要使用的连接。我的程序似乎比我开始跟踪打开的文件描述符之前工作得更好，但我仍然遇到一些同步问题，我不知道如何解决。每个线程的启动路由中的 conn_fd process_connection_request() 似乎正在被破坏。
我尝试在对我的服务器运行 Siege 时使用 Helgrind 来隔离问题。不幸的是，我的代码在 Helgrind 下运行时从未崩溃。它确实表明 conn_fd 存在潜在的竞争条件，但我认为将 main() 和 process_connection_request() 中的互斥体包裹起来可以解决该问题。我以前从未开发过任何多线程或套接字程序，我怀疑我缺少一些简单的东西。非常感谢有关如何解决发送和接收时错误文件描述符问题的任何见解和建议。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <fcntl.h>
#include <time.h>
#include <signal.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define SERVER_PORT 50040
#define MAX_LISTEN_BACKLOG 1024
#define MAX_FILENAME_LENGTH 255
#define REQUEST_BUFF_SIZE 8192
#define THREAD_POOL_SIZE 16
// function prototypes
int int_len(int i);
void *process_connection_request(void *conn_fd);
void sig_handler(int sig);
pthread_t thread;
pthread_attr_t thread_attr;
pthread_mutex_t conn_fd_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t stats_mutex = PTHREAD_MUTEX_INITIALIZER;
int sock_fd;
int conn_fds_open[1000];
int main(void)
{
struct sockaddr_in server_addr;
struct sockaddr_in client_addr;
int conn_fd;
int client_len = sizeof(client_addr);
if((sock_fd = socket(PF_INET, SOCK_STREAM, 0)) < 0)
{
perror("socket() Failed");
exit(EXIT_FAILURE);
}
// set socket options so that we can reuse the socket
const int sock_opt_val = 1;
const socklen_t sock_opt_len = sizeof(sock_opt_val);
setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, (void *) &sock_opt_val, sock_opt_len);
memset(&conn_fds_open, 0, 1000 * sizeof(int));
memset(&server_addr.sin_zero, 0, sizeof(server_addr.sin_zero));
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(SERVER_PORT);
server_addr.sin_addr.s_addr = INADDR_ANY;
if(bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0)
{
perror("bind() Failed");
close(sock_fd);
exit(EXIT_FAILURE);
}
if(listen(sock_fd, MAX_LISTEN_BACKLOG) < 0)
{
perror("listen() Failed");
close(sock_fd);
exit(EXIT_FAILURE);
}
if(pthread_attr_init(&thread_attr) != 0)
{
perror("pthread_attr_init Failed");
close(sock_fd);
exit(EXIT_FAILURE);
}
if(pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_DETACHED) != 0)
{
perror("pthread_attr_setdetachstate Failed");
close(sock_fd);
exit(EXIT_FAILURE);
}
signal(SIGINT, sig_handler);
printf("sock_fd %d\n", sock_fd);
while(1)
{
if((conn_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &client_len)) < 0)
{
perror("accept() Failed");
close(sock_fd);
exit(EXIT_FAILURE);
}
pthread_mutex_lock(&conn_fd_mutex);
if(conn_fds_open[conn_fd] == 1)
{
conn_fd = fcntl(conn_fd, F_DUPFD, 0);
}
conn_fds_open[conn_fd] = 1;
printf("main fd: %d\n", conn_fd);
pthread_mutex_unlock(&conn_fd_mutex);
pthread_create(&thread, &thread_attr, process_connection_request, (void *)&conn_fd);
}
}
int int_len(int i)
{
return (i == 0) ? 1 : floor(log10(abs(i))) + 1;
}
void *process_connection_request(void *conn_fd_ptr)
{
FILE *requested_file = NULL;
FILE *stats_file = NULL;
char *request_buff;
char *response_buff;
char *file_buff;
char *stats_buff;
char *filename_start;
char *filename_stop;
char requested_filename[MAX_FILENAME_LENGTH];
int conn_fd = *(int *)conn_fd_ptr;
int requested_file_size;
int response_buff_size;
int stats_buff_size;
int amt_sent = 0;
int response_code;
time_t now;
char time_buff[30];
time(&now);
strftime(time_buff, 30, "%a, %d %b %Y %X GMT", gmtime(&now));
printf("thread fd: %d\n", conn_fd);
if((request_buff = calloc(REQUEST_BUFF_SIZE, sizeof(char))) == NULL)
{
perror("Calloc Failed");
close(conn_fd);
close(sock_fd);
exit(EXIT_FAILURE);
}
if(recv(conn_fd, (void *)request_buff, REQUEST_BUFF_SIZE, 0) < 0)
{
perror("recv() Failed");
close(conn_fd);
close(sock_fd);
exit(EXIT_FAILURE);
}
// extract the filename from the request header
filename_start = &request_buff[5];
filename_stop = strstr(request_buff, " HTTP");
if((strncmp(request_buff, "GET /", 5) != 0) || (filename_stop == NULL))
{
perror("Invalid Request");
close(conn_fd);
close(sock_fd);
exit(EXIT_FAILURE);
}
strncpy(requested_filename, &request_buff[5], filename_stop - filename_start);
free(request_buff);
requested_filename[filename_stop - filename_start] = '\0';
if((requested_file = fopen(requested_filename, "r")) != NULL)
{
response_code = 200;
fseek(requested_file, 0, SEEK_END);
requested_file_size = ftell(requested_file);
fseek(requested_file, 0, SEEK_SET);
file_buff = calloc(requested_file_size + 1, sizeof(char));
response_buff = calloc((83 + strlen(time_buff) + int_len(requested_file_size) + requested_file_size), sizeof(char));
if(file_buff == NULL || response_buff == NULL)
{
perror("Calloc Failed");
close(conn_fd);
close(sock_fd);
exit(EXIT_FAILURE);
}
fread(file_buff, 1, requested_file_size, requested_file);
response_buff_size = sprintf(response_buff, "HTTP/1.1 200 OK\nDATE: %s\nContent-Length: %d\nConnection: close\nContent-Type: text/html\n\n%s", time_buff, requested_file_size, file_buff);
free(file_buff);
fclose(requested_file);
}
else
{
response_code = 404;
response_buff = malloc(25 * sizeof(char));
strcpy(response_buff, "HTTP/1.1 404 Not Found\n\n");
response_buff_size = 25;
}
while(amt_sent < response_buff_size)
{
int ret = send(conn_fd, response_buff + amt_sent, response_buff_size - amt_sent, 0);
if (ret < 0)
{
perror("send() Failed.");
close(conn_fd);
close(sock_fd);
exit(EXIT_FAILURE);
}
amt_sent += ret;
}
free(response_buff);
pthread_mutex_lock(&conn_fd_mutex);
conn_fds_open[conn_fd] = 0;
close(conn_fd);
pthread_mutex_unlock(&conn_fd_mutex);
// yield to any other connection threads before writing to the stats file
pthread_yield();
pthread_mutex_lock(&stats_mutex);
if((stats_file = fopen("stats.txt", "a")) != NULL)
{
if((stats_buff = malloc((strlen(time_buff) + 51 + strlen(requested_filename)) * sizeof(char))) != NULL)
{
stats_buff_size = sprintf(stats_buff, "Date - %s | Response Code - %d | Requested File - %s\n", time_buff, response_code, requested_filename);
fwrite(stats_buff, stats_buff_size, 1, stats_file);
free(stats_buff);
}
fclose(stats_file);
}
pthread_mutex_unlock(&stats_mutex);
}
void sig_handler(int sig)
{
close(sock_fd);
exit(0);
}
