linux 多線程編程（二）

六、三線程讀寫緩衝區

  1 #include <stdio.h>
  2 #include <stdlib.h>
  3 #include <unistd.h>
  4 #include <pthread.h>
  5 #include<string.h>
  6 char buf[50];
  7 void *twrite(char *arg)
  8 {
  9         strcpy(buf+strlen(buf),arg);
 10         printf("write success\n");
 11 }
 12 void *tread()
 13 {
 14         printf("read:%s\n",buf);
 15 }
 16 int main()
 17 {
 18         pthread_t id1,id2,id3;
 19         char *s1="I am write1\n";
 20         char *s2="I am write2\n";
 21         pthread_create(&id1,NULL,twrite,s1);
 22         pthread_join(id1,NULL);
 23         pthread_create(&id2,NULL,twrite,s2);
 24         pthread_join(id2,NULL);
 25         pthread_create(&id3,NULL,tread,NULL);
 26         pthread_join(id3,NULL);
 27         printf("I am main\n");
 28         return 0;
 29 }

執行結果：

write success
write success
read:I am write1
I am write2
I am main

七、三線程讀寫有名管道

 1 #include <stdio.h>
  2 #include <stdlib.h>
  3 #include <unistd.h>
  4 #include <pthread.h>
  5 #include<string.h>
  6 #include<fcntl.h>
  7 #include<sys/stat.h>
  8 #include<sys/types.h>
  9 #define FIFO "myfifo"
 10 void *twrite(char *arg)
 11 {
 12         int fd;
 13         umask(0);
 14         fd=open(FIFO,O_WRONLY|O_NONBLOCK);
 15         write(fd,arg,strlen(arg)+1);
 16         printf("write success\n");
 17 }
 18 void *tread()
 19 {
 20         int fd;
 21         char buf[1024];
 22         umask(0);
 23         fd=open(FIFO,O_RDONLY|O_NONBLOCK);
 24         read(fd,buf,1024);
 25         printf("read:%s\n",buf);
 26 }       

 27 int main()
 28 {
 29         pthread_t id1,id2,id3;
 30         char *s1="I am write1\n";
 31         char *s2="I am write2\n";
 32         mkfifo(FIFO,O_CREAT|O_EXCL|0777);
 33         pthread_create(&id3,NULL,tread,NULL);
 34         pthread_join(id3,NULL);
 35         pthread_create(&id1,NULL,twrite,s1);
 36         pthread_join(id1,NULL);
 37         pthread_create(&id3,NULL,tread,NULL);
 38         pthread_join(id3,NULL);
 39         pthread_create(&id2,NULL,twrite,s2);
 40         pthread_join(id2,NULL);
 41         pthread_create(&id3,NULL,tread,NULL);
 42         pthread_join(id3,NULL);
 43         return 0;
 44 }

執行結果：

read:
write success
read:I am write1


write success
read:I am write2

問題：

如果註釋掉33、34。第一次讀出的是亂碼？？？