1、linux下c语言编程4使用共享内存实现进程间通信linux下C语言编程4-使用共享内存实现进程间通信共享内存的函数有以下几个:(1)int shmget(key_t key, int size, int shmflg),开辟或使用一块共享内存。(2)void *shmat(int shmid, const void *shmaddr, int shmflg), 将参数shmid所指向的共享内存与当前进程连接。当使用某共享内存时,需要先使用shmat,达成连接。(3)int shmdt(const void *shmaddr),将先前用shmat连接的共享内存与当前进程解除连接。参数shmad
2、dr为shmat返回的共享内存的地址。在完成对共享内存的使用后,需要使用shmdt解除连接。(4)int shmctl(int shmid, int cmd, struct shmid_ds *buf),控制内存的操作。当cmd为IPC_RMID时,删除shmid所指的共享内存。这些函数的表头文件为和,其详细参数请去网上搜索。下面给出一个使用共享内存实现进程间通信的例子:进程A开辟一块新的共享内存,进程B修改这个共享内存,进程C打印输出这个共享内存的内容,进程D删除这个共享内存。进程BCD运行的命令格式为:命令 共享内存ID,如./output 123432。进程A代码如下:int main(
3、) int shmid; shmid = shmget(IPC_PRIVATE, SIZE, IPC_CREAT | 0600); if (shmid 0) perror(shmget error); exit(1); printf(create shared memory OK. shmid=%d/n, shmid); return 0;进程B代码如下:int main(int argc, char *argv) int shmid; char *shmaddr; if (argc != 2) perror(argc error/n); exit(1); shmid = atoi(argv1
4、); shmaddr = (char *)shmat(shmid, NULL, 0); if (int )shmaddr = -1) perror(shmat error./n); exit(1); strcpy(shmaddr, hello, world!); shmdt(shmaddr); return 0; 进程C代码如下:int main(int argc, char *argv) int shmid; char *shmaddr; if (argc != 2) printf(argc error/n); exit(1); shmid = atoi(argv1); shmaddr =
5、(char *)shmat(shmid, NULL, 0); if (int )shmaddr = -1) perror(shmat error./n); exit(1); printf(%s/n, shmaddr); shmdt(shmaddr); return 0; 进程D代码如下:int main(int argc, char *argv) int shmid; if (argc != 2) perror(argc error/n); exit(1); shmid = atoi(argv1); shmctl(shmid, IPC_RMID, NULL); return 0; linux下
6、C语言编程5-多线程编程 Linux系统下的多线程遵循POSIX线程接口,称为pthread。编写Linux下的多线程程序,需要使用头文件pthread.h,编译需要在后面加-lpthread。关于多线程,主要有以下几个过程:1,创建线程2,各个线程的执行3,等待线程的结束涉及的线程函数主要有:1,int pthread_create(pthread_t *restrict tidp, const pthread_attr_t *restrict attr, void *(*start_rtn)(void),void *restrict arg);函数有4个参数:第一个参数为指向线程标识符的指
7、针。第二个参数用来设置线程属性。第三个参数是一个函数指针(有关函数指针,看这里),指向线程运行函数的起始地址。最后一个参数是函数指针所需要的参数。注意:pthread_create函数返回0表示成功。另外如果函数指针需要多个参数的话,就将这些参数做成某个结构体,作为第4个参数。如果有返回值的话,也可将返回值的指针回写到第4个参数中。2,pthread_join()等待一个线程的结束。pthread_exit()用于线程退出,可以指定返回值,以便其他线程通过pthread_join()函数获取该线程的返回值。线程的应用:并行数据库的查询假设我们有3台计算机A, B, C,每台均安装PG数据库,通
8、过网络连接。我们可以通过多线程将查询SQL广播出去,A,B,C并行查询,最终返回各自的结果。如果没有多线程,而只是用了个循环,那么我们获取结果的过程将是顺序的,即等A的结果返回后才能查询B,B结束后查询C,效率低下。代码如下:/最多支持MAX个线程 #define MAX 16 /* 多线程 */ typedef struct PDthread char *host; / IP int port; / 端口 char *dbname; / 数据库名 char *query; / SQL语句 void *rst; / 查询结果 PDthread; typedef struct Nodes int
9、 count; / 实际上的节点数量countrst = (void *)ExecuteQuery(p-host, p-port, p-dbname, p-query); pthread_exit(NULL); return NULL; /* 创建多个线程,1个node对应1个线程 * 输出:thread, pdthread * 输入:node, dbname, query, 这些值写到pdthread变量中,传递给函数PDthreadSelect(因为此函数只能有一个参数) */void PDthreadCreate(pthread_t thread, PDthread *pdthread,
10、 Nodes *node, char *dbname, char *query) int tmp; int i; PDthread *p; for (i=0; icount; i+) / 把Nodes作为PDthread的一部分 p = pdthread + i; p-host = node-hosti; p-port = node-porti; p-dbname = dbname; p-query = query; tmp = pthread_create(&threadi, NULL, PDthreadSelect, p); if (tmp != 0) printf(PDthreadCre
11、ate: 线程%d创建失败!/n, i); else printf(PDthreadCreate: 线程%d被创建/n, i); void PDthreadWait(pthread_t thread, int count) / 等待线程结束 int i; for (i=0; irst return 0; 编译命令:gcc -I/usr/local/pgsql/include -o th th.c -L/usr/local/pgsql/lib -lpq -lpthread,因为使用了libpq库。Linux下通过共享内存进行进程间通信,进程间同步使用信号量来实现(Linux 环境下C编程指南)
12、Linux 环境下C编程指南,通过共享内存进行进程间通信的例子,进程间同步使用信号量来实现。使用说明:这是一个简单的服务器和客户端程序,如果启动程序时不带参数,则执行服务器程序;如果带参数,则执行客户端程序,所带参数只有一个,就是服务器端所显示的共享内存的引用ID。实现原理:服务器端启动后,创建信号量和共享内存,并将共享内存的引用ID显示出来,将信号量的引用ID存放在共享内存中。客户端启动后,利用服务器端提供的内存共享ID将共享内存附加到地址段,读取信号量以实现两个进程之间的同步。之后,这两个进程就可以利用共享内存进行进程间通信,客户端输入的信息将在服务器端显示出来。 #include #in
13、clude #include #include #include #include #include #include #include #define SHMDATASIZE 1000#define BUFFERSIZE (SHMDATASIZE - sizeof(int)#define SN_EMPTY 0#define SN_FULL 1int deleteSemid=0;union semun int val; struct semid_ds *buf; unsigned short int *array; struct seminfo *_buf; ;void server(void
14、); /不加参数时执行void client(int shmid);void delete(void);void sigdelete(int signum);void locksem(int semid, int semnum);void unlocksem(int semid, int semnum);void waitzero(int semid, int semnum);void clientwrite(int shmid, int semid, char *buffer);int safesemget(key_t key, int nsems, int semflg);int safe
15、semctl(int semid, int semnum, int cmd, union semun arg);int safesemop(int semid, struct sembuf *sops, unsigned nsops);int safeshmget(key_t key, int size, int shmflg);void *safeshmat(int shmid, const void *shmaddr, int shmflg);int safeshmctl(int shmid, int cmd, struct shmid_ds *buf);int main(int argc
16、, char *argv) if ( argc 2 ) server(); else client(atoi(argv1); return 0;void server(void) union semun sunion; int semid,shmid; void *shmdata; char *buffer; semid = safesemget(IPC_PRIVATE, 2, SHM_R|SHM_W); deleteSemid = semid; atexit(&delete); /当程序终止执行时,执行 delete 函数 signal(SIGINT, &sigdelete); /接收到信号
17、 SIGINT 则执行 sigdelete 函数 sunion.val = 1; safesemctl(semid, SN_EMPTY, SETVAL, sunion); sunion.val = 0; safesemctl(semid, SN_FULL, SETVAL, sunion); shmid = safeshmget(IPC_PRIVATE, SHMDATASIZE, IPC_CREAT|SHM_R|SHM_W); shmdata = safeshmat(shmid, 0, 0); safeshmctl(shmid, IPC_RMID, NULL); /删除共享内存,当所有附加该共享
18、内存的进程结束或断开与该共享内存的连接时才执行 *(int *)shmdata = semid; buffer = shmdata + sizeof(int); printf(Server is running with SHM id * %d *n, shmid); while(1) printf(Waiting until full.); fflush(stdout); locksem(semid, SN_FULL); printf(done.n); printf(Message received: %s.n, buffer); unlocksem(semid, SN_EMPTY); vo
19、id client(int shmid) int semid; void *shmdata; char *buffer; shmdata = safeshmat(shmid, 0, 0); semid = *(int *)shmdata; buffer = shmdata + sizeof(int); printf(Client operational: shm id is %d, sem id is %dn, shmid, semid); while(1) char input3; printf(nnMenun1.send a messagen); printf(2.Exitn); fget
20、s(input, sizeof(input), stdin); switch(input0) case 1: clientwrite(shmid, semid, buffer); break; case 2: exit(0); break; void delete(void) printf(nMaster exiting; deleting semaphore %d.n, deleteSemid); if (semctl(deleteSemid, 0, IPC_RMID, 0) = -1 ) printf(Error releasing semaphore.n); void sigdelete
21、(int signum) exit(0);void locksem(int semid, int semnum) struct sembuf sb; sb.sem_num = semnum; sb.sem_op = -1; sb.sem_flg = SEM_UNDO; safesemop(semid, &sb, 1);void unlocksem(int semid, int semnum) struct sembuf sb; sb.sem_num = semnum; sb.sem_op = 1; sb.sem_flg = SEM_UNDO; safesemop(semid, &sb, 1);
22、void waitzero(int semid, int semnum) struct sembuf sb; sb.sem_num = semnum; sb.sem_op = 0; sb.sem_flg = 0; safesemop(semid, &sb, 1);void clientwrite(int shmid, int semid, char *buffer) printf(Waiting until empty.); fflush(stdout); locksem(semid, SN_EMPTY); printf(done.n); printf(Enter Message: ); fg
23、ets(buffer, BUFFERSIZE, stdin); unlocksem(semid, SN_FULL);int safesemget(key_t key, int nsems, int semflg) int retval; if ( (retval=semget(key, nsems, semflg) = -1) printf(semget error: %s.n, strerror(errno); exit(254); return retval;int safesemctl(int semid, int semnum, int cmd, union semun arg) in
24、t retval; if ( (retval=semctl(semid, semnum, cmd, arg) = -1) printf(semctl error: %s.n, strerror(errno); exit(254); return retval;int safesemop(int semid, struct sembuf *sops, unsigned nsops) int retval; if ( (retval=semop(semid, sops, nsops) = -1) printf(semop error: %s.n, strerror(errno); exit(254); return retval;int safeshmget(key_t key, int size, int shmflg) int retval; if ( (retval=shmget(key, size, shmflg) = -1) printf(shmget error: %s.n, strerror(errno); exit(254); return retval;void *safes
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