如何在线程之间共享变量？
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【中文标题】如何在线程之间共享变量？【英文标题】：How to share variables among threads? 【发布时间】：2021-01-27 03:35:11 【问题描述】：我正在开发一个允许服务器交换消息的服务器-客户端项目 单独与一个客户。但是，我必须修改服务器，以便在服务器发送消息时，将消息发送到所有连接的客户端。
我知道这涉及在线程之间共享变量，但我对如何去做这件事感到困惑？
任何提示/指导将不胜感激！
服务器代码：
#include<stdio.h>
#include<string.h> //strlen
#include<stdlib.h> //strlen
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
#include<unistd.h> //write
#include<pthread.h> //for threading , link with lpthread
#define MAX 80
#define PORT 6543
#define SA struct sockaddr
// Function designed for chat between client and server.
void join( pthread_t *thread_id)
if(!pthread_join( *thread_id , NULL))
printf("thread %ld complted\n",*thread_id);
pthread_exit(0);//to exit the current thread
void func(int *sockfd)
char buff[MAX];
int n;
// infinite loop for chat
for (;;)
bzero(buff, MAX);
// read the message from client and copy it in buffer
read(*sockfd, buff, sizeof(buff));
// print buffer which contains the client contents
printf("From client: %s\t To client : ", buff);
bzero(buff, MAX);
n = 0;
// copy server message in the buffer
while ((buff[n++] = getchar()) != '\n');
// and send that buffer to client
write(*sockfd, buff, sizeof(buff));
// if msg contains "Exit" then server exit and chat ended.
if (strncmp("exit", buff, 4) == 0)
printf("Server Exit...\n");
break;
// Driver function
int main()
int sockfd, connfd, len;
struct sockaddr_in servaddr, cli;
pthread_t thread_id,jointhread_id;
// socket create and verification
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1)
printf("socket creation failed...\n");
exit(0);
else
printf("Socket successfully created..\n");
bzero(&servaddr, sizeof(servaddr));
// assign IP, PORT
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(PORT);
// Binding newly created socket to given IP and verification
if ((bind(sockfd, (SA*)&servaddr, sizeof(servaddr))) != 0)
printf("socket bind failed...\n");
exit(0);
else
printf("Socket successfully binded..\n");
// Now server is ready to listen and verification
if ((listen(sockfd, 5)) != 0)
printf("Listen failed...\n");
exit(0);
else
printf("Server listening..\n");
len = sizeof(cli);
// Accept the data packet from client and verification
while(connfd = accept(sockfd, (SA*)&cli, &len))
if (connfd < 0)
printf("server acccept failed...\n");
exit(0);
else
printf("server acccept the client..%d.\n",connfd);
if( pthread_create( &thread_id , NULL , func , (void*) &connfd) < 0)
perror("could not create thread");
return 1;
if( pthread_create( &jointhread_id , NULL , join , (void*) &thread_id) < 0)
perror("could not create thread");
return 1;
// After chatting close the socket
close(sockfd);
【问题讨论】：
旁注：您的代码中有竞争条件。这是因为您将connfd 传递为&connfd。由于线程正在执行*sockfd，如果accept 返回足够快，connfd [in main] 中的值可能会更改为 后续 线程的值。该线程会看到sockfd 发生不可预测的变化。解决方法是通过 value 传递 connfd。这样做：pthread_create(...,(void *) connfd); 并将 func 更改为：void func(void *ptr) int sockfd = (int) ptr; ...
【参考方案1】：
不幸的是，有许多错误......
线程函数的原型错误
connfd 的竞争条件，如我的*** cmets 中所述（将 connfd 作为指针传递给 func）。
执行getchar 会破坏来自sockfd 读取的消息数据
我在下面制作了一个版本来说明这一点。
但是，要真正使代码更接近您声明的目的所需的代码，需要进行大量的重构。下面还有第二个版本说明了我对此的看法。
这是一个带注释的版本，其中显示了错误和一些修复 [主要是让它干净编译所需的内容]。
它用#if ORIG 包装原始代码，用#if FIX 包装新代码，每个地方都有关于它正在修复的错误的评论
#include <stdio.h>
#include <string.h> // strlen
#include <stdlib.h> // strlen
#include <sys/socket.h>
#include <arpa/inet.h> // inet_addr
#include <unistd.h> // write
#include <pthread.h> // for threading , link with lpthread
#define MAX 80
#define PORT 6543
#define SA struct sockaddr
#define ORIG 0
#define FIX 1
// Function designed for chat between client and server.
// NOTE/BUG -- the main thread has to join the thread
#if ORIG
void
join(pthread_t *thread_id)
if (!pthread_join(*thread_id, NULL))
printf("thread %ld complted\n", *thread_id);
// to exit the current thread
pthread_exit(0);
#endif
// NOTE/BUG: this is the _wrong_ signature for a thread function
#if ORIG
void
func(int *sockfd)
#else
void *
func(void *ptr)
#endif
#if FIX
int sockfd = (long) ptr;
#endif
char buff[MAX];
int n;
// infinite loop for chat
for (;;)
bzero(buff, MAX);
// read the message from client and copy it in buffer
// NOTE/BUG: this has a race condition
// NOTE/BUG: we need the actual length
#if ORIG
read(*sockfd, buff, sizeof(buff));
#else
int rlen = read(sockfd, buff, sizeof(buff));
#endif
// print buffer which contains the client contents
printf("From client: %s\t To client : ", buff);
bzero(buff, MAX);
// copy server message in the buffer
// NOTE/BUG: this is destroying the data that was
#if ORIG
n = 0;
while ((buff[n++] = getchar()) != '\n');
#endif
// and send that buffer to client
#if ORIG
write(*sockfd, buff, sizeof(buff));
#else
write(sockfd, buff, rlen);
#endif
// if msg contains "Exit" then server exit and chat ended.
if (strncmp("exit", buff, 4) == 0)
printf("Server Exit...\n");
break;
// NOTE/BUG: we must return the error code
#if FIX
return (void *) 0;
#endif
// Driver function
int
main()
int sockfd, connfd, len;
struct sockaddr_in servaddr, cli;
pthread_t thread_id, jointhread_id;
// socket create and verification
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1)
printf("socket creation failed...\n");
exit(0);
else
printf("Socket successfully created..\n");
// assign IP, PORT
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(PORT);
// Binding newly created socket to given IP and verification
if ((bind(sockfd, (SA *) & servaddr, sizeof(servaddr))) != 0)
printf("socket bind failed...\n");
exit(0);
else
printf("Socket successfully binded..\n");
// Now server is ready to listen and verification
if ((listen(sockfd, 5)) != 0)
printf("Listen failed...\n");
exit(0);
else
printf("Server listening..\n");
// Accept the data packet from client and verification
len = sizeof(cli);
// NOTE/BUG: connfd can be zero for a valid connection
#if ORIG
while (connfd = accept(sockfd, (SA *) &cli, &len))
#else
while (1)
connfd = accept(sockfd, (SA *) &cli, &len);
#endif
if (connfd < 0)
printf("server acccept failed...\n");
exit(0);
else
printf("server acccept the client..%d.\n", connfd);
#if ORIG
if (pthread_create(&thread_id, NULL, func, (void *) &connfd) < 0)
perror("could not create thread");
return 1;
#else
if (pthread_create(&thread_id, NULL, func, (void *) ((long) connfd)) < 0)
perror("could not create thread");
return 1;
#endif
// NOTE/BUG -- creating a separate thread just to join the above thread does
// not help
#if ORIG
if (pthread_create(&jointhread_id, NULL, join, (void *) &thread_id) < 0)
perror("could not create thread");
return 1;
#endif
// After chatting close the socket
close(sockfd);
return 0;
这是一个重构版本，它实现了您想要的多客户端消息回显。
它使用每个线程的任务块来控制事物。每个客户端在收到消息后，将其发送给所有其他客户端。
它还使用互斥锁进行一些线程间锁定。
让一个给定的客户端线程向其他客户端执行所有回显只是一种方法。还有其他的（例如，所有客户端线程将消息排队到主/主线程，它做回声）
这更接近了，但您需要在func 中完成更多工作来接收/发送客户端消息。
不管怎样，代码如下：
#include <stdio.h>
#include <string.h> // strlen
#include <stdlib.h> // strlen
#include <sys/socket.h>
#include <arpa/inet.h> // inet_addr
#include <unistd.h> // write
#include <pthread.h> // for threading , link with lpthread
#define MAX 80
#define PORT 6543
#define SA struct sockaddr
#define ORIG 0
#define FIX 1
enum
TSKSTATE_IDLE, // task slot free/available
TSKSTATE_PENDING, // task is being created
TSKSTATE_RUNNING, // task is alive and running
TSKSTATE_DONE // task has completed (but not reaped)
;
typedef struct tsk tsk_t;
struct tsk
tsk_t *tsk_next; // chain pointer
pthread_t tsk_tid; // thread id
long tsk_xid; // sequential task id
int tsk_sockfd; // client socket descriptor
int tsk_state; // current task state
pthread_mutex_t tsk_mutex; // per-thread mutex
void *tsk_rtn; // thread's return value
;
// NOTE: using an array obviates the need for a master lock if we used a
// linked list here instead -- by passing TSKMAX to listen below [in main],
// we guarantee that main can always find a free task slot when it needs one
#define TSKMAX 5
tsk_t tsklist[TSKMAX]; // active task list
#define TSKFORALL(_tsk) \
_tsk = &tsklist[0]; _tsk < &tsklist[TSKMAX]; ++_tsk
long tskxid; // sequential task id
__thread tsk_t *tskcur; // current thread's tsk block
pthread_mutex_t master_lock = PTHREAD_MUTEX_INITIALIZER;
// lockall -- lock all threads
void
lockall(void)
pthread_mutex_lock(&master_lock);
// unlockall -- lock all threads
void
unlockall(void)
pthread_mutex_unlock(&master_lock);
// tsklock -- lock single thread
void
tsklock(tsk_t *tsk)
pthread_mutex_lock(&tsk->tsk_mutex);
// tskunlock -- unlock single thread
void
tskunlock(tsk_t *tsk)
pthread_mutex_unlock(&tsk->tsk_mutex);
// tskreapall -- release all completed threads
void
tskreapall(void)
tsk_t *tsk;
lockall();
for (TSKFORALL(tsk))
tsklock(tsk);
if (tsk->tsk_state == TSKSTATE_DONE)
pthread_join(tsk->tsk_tid,&tsk->tsk_rtn);
tsk->tsk_state = TSKSTATE_IDLE;
tskunlock(tsk);
// tsksendall -- send message to all other clients
void
tsksendall(char *msg,int len)
tsk_t *tsk;
lockall();
for (TSKFORALL(tsk))
if (tsk == tskcur)
continue;
tsklock(tsk);
if (tsk->tsk_state == TSKSTATE_RUNNING)
write(tsk->tsk_sockfd,msg,len);
tskunlock(tsk);
void *
func(void *ptr)
tskcur = ptr;
char buff[MAX];
#if ORIG
int n;
#endif
tsklock(tskcur);
tskcur->tsk_state = TSKSTATE_RUNNING;
tskunlock(tskcur);
// infinite loop for chat
// NOTE: this loop still needs work ...
for (;;)
bzero(buff, MAX);
// read the message from client and copy it in buffer
int rlen = read(tskcur->tsk_sockfd, buff, sizeof(buff));
// print buffer which contains the client contents
printf("From client: %s\t To client : ", buff);
bzero(buff, MAX);
// copy server message in the buffer
// NOTE/BUG: this is destroying the data that was
#if ORIG
n = 0;
while ((buff[n++] = getchar()) != '\n');
#endif
// and send that buffer to client
write(tskcur->tsk_sockfd, buff, rlen);
// if msg contains "Exit" then server exit and chat ended.
if (strncmp("exit", buff, 4) == 0)
printf("Server Exit...\n");
break;
// echo message to all other clients
tsksendall(buff,rlen);
tsklock(tskcur);
tskcur->tsk_state = TSKSTATE_DONE;
close(tskcur->tsk_sockfd);
tskcur->tsk_sockfd = -1;
tskunlock(tskcur);
return (void *) 0;
// Driver function
int
main(void)
int sockfd, connfd;
socklen_t len;
struct sockaddr_in servaddr, cli;
int state;
tsk_t *tsktry;
tsk_t *tsknew;
// socket create and verification
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1)
printf("socket creation failed...\n");
exit(0);
else
printf("Socket successfully created..\n");
// assign IP, PORT
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(PORT);
// Binding newly created socket to given IP and verification
if ((bind(sockfd, (SA *) & servaddr, sizeof(servaddr))) != 0)
printf("socket bind failed...\n");
exit(0);
else
printf("Socket successfully binded..\n");
// Now server is ready to listen and verification
if ((listen(sockfd, TSKMAX)) != 0)
printf("Listen failed...\n");
exit(0);
else
printf("Server listening..\n");
// Accept the data packet from client and verification
len = sizeof(cli);
for (TSKFORALL(tsktry))
pthread_mutex_init(&tsktry->tsk_mutex,NULL);
tsktry->tsk_state = TSKSTATE_IDLE;
while (1)
connfd = accept(sockfd, (SA *) &cli, &len);
if (connfd < 0)
printf("server acccept failed...\n");
exit(0);
else
printf("server acccept the client..%d.\n", connfd);
// reap all completed threads
tskreapall();
// find an idle slot
tsknew = NULL;
for (TSKFORALL(tsktry))
tsklock(tsktry);
state = tsktry->tsk_state;
if (state == TSKSTATE_IDLE)
tsknew = tsktry;
tsknew->tsk_state = TSKSTATE_PENDING;
tskunlock(tsktry);
if (tsknew != NULL)
break;
tsknew->tsk_xid = ++tskxid;
tsknew->tsk_sockfd = connfd;
if (pthread_create(&tsknew->tsk_tid, NULL, func, tsknew) < 0)
perror("could not create thread");
return 1;
// After chatting close the socket
close(sockfd);
return 0;
【讨论】：
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