1. 線程同步
a. 需要線程同步的情況:1)同時訪問同一內存空間;2)需要指定訪問同一內存空間的線程執行順序。
b. 同步技術:互斥量Mutex和信號量Semaphore
將臨界區比喻成洗手間,線程同步理解成一把鎖。
爲了保護個人隱私,進洗手間時鎖上門,出來再打開;
如果有人使用洗手間,其他人需要在外面等待;
等待的人數可能很多,這些人需要排隊進入洗手間。
2. 互斥量Mutual Exclusion,創建和銷燬函數
#include <pthread.h>
int pthread_mutex_init(pthread_mutex_t * mutex,const pthread_mutexattr_t * attr);
int pthread_mutex_destroy(pthread_mutex_t * mutex);
成功返回0,失敗返回其他值
mutex:創建/銷燬互斥量時傳遞保存互斥量的變量地址值
attr:創建的互斥量屬性
但是最好還是使用函數,宏比較難檢查錯誤。
3. 互斥量鎖住、釋放臨界區
int pthread_mutex_lock(pthread_mutex_t * mutex);
int pthread_mutex_unlock(pthread_mutex_t *mutex);
成功返回0,失敗返回其他值
注意:臨界區鎖住後,忘記解鎖,則其他嘗試進入臨界區的線程將會“死鎖”。
4. 信號量的創建、銷燬
int sem_init(sem_t *sem,int pshared,unsigned int value);
int sem_destroy(sem_t * sem);
成功返回0,失敗返回其他值
sem:創建信號量時傳遞保存信號量的變量地址值
pshared:傳遞其他值時,可創建多個進程共享的信號量。0時,只允許一個進程內部使用該信號量
value:指定信號量初始值。
5. post/wait
int sem_post(sem_t *sem);
int sem_wait(sem_t *sem);
成功返回0,失敗時返回其他值
sem:傳遞保存信號量讀取值得變量地址值
調用sem_post函數值,對象+1,sem_wait函數時-1.
信號量的值不能小於0,在信號量爲0的情況,sem_wait函數會進入阻塞直到值大於0。
6. 關於控制訪問順序的同步
代碼:
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
void * read(void * arg);
void * accu(void * arg);
static sem_t sem_one;
static sem_t sem_two;
static int num;
int main(int argc, char *argv[]){
pthread_t id_t1,id_t2;
sem_init(&sem_one,0,0);
sem_init(&sem_two,0,1);
pthread_create(&id_t1,NULL,read,NULL);
pthread_create(&id_t2,NULL,accu,NULL);
pthread_join(id_t1,NULL);
pthread_join(id_t2,NULL);
sem_destroy(&sem_one);
sem_destroy(&sem_two);
return 0;
}
void * read(void * arg){
int i;
for(i=0;i<5;i++){
printf("Input num %d: ",i+1);
sem_wait(&sem_two);
scanf("%d",&num);
sem_post(&sem_one);
}
return NULL;
}
void *accu(void *arg){
int sum = 0,i;
for(i=0;i<5;i++){
sem_wait(&sem_one);
sum += num;
printf("sum = %d \n",sum);
sem_post(&sem_two);
}
printf("result : %d \n",sum);
return NULL;
}
執行結果:
alex@alex-VirtualBox:~/Share/Test/tcpip$ ./sema
Input num 1: 123
sum = 123
Input num 2: 123
Input num 3: sum = 246
1
Input num 4: sum = 247
1
Input num 5: sum = 248
1
sum = 249
result : 249
7. 線程的銷燬
線程不是在線程main返回時自動銷燬,而是使用下面的方法銷燬,不然會一直存在內存空間:
a. pthread_join函數//線程一直等待,阻塞
b. pthread_detach函數//通常使用這種方法銷燬線程,不會引起線程終止或進入阻塞。
調用個了pthread_detach後,不能再調用pthread_join
int pthread_detach(pthread_t thread);
成功:返回0,失敗返回其他值
8. 多線程併發服務器端的實現
chat_server.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <pthread.h>
#include <semaphore.h>
#define BUF_SIZE 100
#define MAX_CLNT 256
void * handle_clnt(void * arg);
void send_msg(char *msg,int len);
void error_handling(char *message);
int clnt_cnt = 0;
int clnt_socks[MAX_CLNT];
pthread_mutex_t mutx;
int main(int argc, char *argv[]){
int serv_sock;
int clnt_sock;
struct sockaddr_in serv_adr;
struct sockaddr_in clnt_adr;
int clnt_adr_sz;
pthread_t t_id;
if(argc != 2){
printf("Usage : %s <port>\n",argv[0]);
exit(1);
}
pthread_mutex_init(&mutx,NULL);
serv_sock = socket(PF_INET,SOCK_STREAM,0);
if(serv_sock == -1){
error_handling("socket() error");
}
memset(&serv_adr,0,sizeof(serv_adr));
serv_adr.sin_family=AF_INET;
serv_adr.sin_addr.s_addr=htonl(INADDR_ANY);
serv_adr.sin_port=htons(atoi(argv[1]));
if(bind(serv_sock,(struct sockaddr*)&serv_adr,sizeof(serv_adr)) == -1){
error_handling("bind() error");
}
if(listen(serv_sock,5) == -1){
error_handling("listen() error");
}
while(1){
clnt_adr_sz = sizeof(clnt_adr);
clnt_sock = accept(serv_sock,(struct sockaddr*)&clnt_adr,&clnt_adr_sz);
pthread_mutex_lock(&mutx);
clnt_socks[clnt_cnt++] = clnt_sock;
pthread_mutex_unlock(&mutx);
pthread_create(&t_id,NULL,handle_clnt,(void *)&clnt_sock);
pthread_detach(t_id);
printf("Connetcted client IP :%s \n",inet_ntoa(clnt_adr.sin_addr));
}
close(serv_sock);
return 0;
}
void error_handling(char *message){
fputs(message,stderr);
fputs("\n",stderr);
exit(1);
}
void * handle_clnt(void * arg){
int clnt_sock = *((int *)arg);
int str_len =0;
int i;
char msg[BUF_SIZE];
while((str_len = read(clnt_sock,msg,sizeof(msg))) != 0)
send_msg(msg,str_len);
pthread_mutex_lock(&mutx);
for(i=0;i<clnt_cnt;i++){
if(clnt_sock == clnt_socks[i]){
while(i++ < clnt_cnt - 1)
clnt_socks[i] = clnt_socks[i+1];
break;
}
}
clnt_cnt--;
pthread_mutex_unlock(&mutx);
close(clnt_sock);
return NULL;
}
//send to all
void send_msg(char *msg,int len)
{
int i;
pthread_mutex_lock(&mutx);
for(i=0;i<clnt_cnt;i++){
write(clnt_socks[i],msg,len);
}
pthread_mutex_unlock(&mutx);
}
執行結果:
alex@alex-VirtualBox:~/Share/Test/tcpip$ gcc chat_server.c -o server -D_REENTRANT -lpthread
alex@alex-VirtualBox:~/Share/Test/tcpip$ ./server 9190
Connetcted client IP :127.0.0.1
Connetcted client IP :192.168.1.104
chat_client.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <semaphore.h>
#include <pthread.h>
#define BUF_SIZE 100
#define NAME_SIZE 20
void error_handling(char *message);
void * send_msg(void * arg);
void * recv_msg(void * arg);
char name[NAME_SIZE] = "[DEFAULT]";
char msg[BUF_SIZE];
int main(int argc,char *argv[]){
int sock;
struct sockaddr_in serv_adr;
pthread_t snd_thread,rcv_thread;
void * thread_return;
if(argc != 4){
printf("Usage : %s <IP> <port> <name>\n",argv[0]);
exit(1);
}
sprintf(name,"[%s]",argv[3]);
sock = socket(PF_INET,SOCK_STREAM,0);
if(sock == -1){
error_handling("socket() error");
}
memset(&serv_adr,0,sizeof(serv_adr));
serv_adr.sin_family = AF_INET;
serv_adr.sin_addr.s_addr = inet_addr(argv[1]);
serv_adr.sin_port = htons(atoi(argv[2]));
if(connect(sock,(struct sockaddr *)&serv_adr,sizeof(serv_adr)) == -1){
error_handling("connect() error\r\n");
}else{
printf("Connected....");
}
pthread_create(&snd_thread,NULL,send_msg,(void *)&sock);
pthread_create(&rcv_thread,NULL,recv_msg,(void *)&sock);
pthread_join(snd_thread,&thread_return);
pthread_join(rcv_thread,&thread_return);
close(sock);
return 0;
}
void error_handling(char *message){
fputs(message,stderr);
fputs("\n",stderr);
exit(1);
}
void * send_msg(void *arg){
int sock = *((int *)arg);
char name_msg[NAME_SIZE + BUF_SIZE];
while(1){
fgets(msg,BUF_SIZE,stdin);
if(!strcmp(msg,"q\n") || ! strcmp(msg,"Q\n")){
close(sock);
exit(0);
}
sprintf(name_msg,"%s %s",name,msg);
write(sock,name_msg,strlen(name_msg));
}
return NULL;
}
void * recv_msg(void * arg){
int sock = *((int *)arg);
char name_msg[NAME_SIZE + BUF_SIZE];
int str_len;
while(1){
str_len = read(sock,name_msg,NAME_SIZE+BUF_SIZE-1);
if(str_len == -1){
return (void *) -1;
}
name_msg[str_len] = 0;
fputs(name_msg,stdout);
}
return NULL;
}
執行結果:
alex@alex-VirtualBox:~/Share/Test/tcpip$ gcc chat_client.c -o client -D_REENTRANT -lpthread
alex@alex-VirtualBox:~/Share/Test/tcpip$ ./client 192.168.1.104 9190 alex
Connected....[stoney] hello
hi
[alex] hi
alex@alex-VirtualBox:~/Share/Test/tcpip$ ./client 127.0.0.1 9190 stoney
Connected....hello
[stoney] hello
[alex] hi