}
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）
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
#define BUFFERSIZE (SHMDATASIZE - sizeof(int)) #define SN_EMPTY 0 #define SN_FULL 1 int deleteSemid=0;
union semun {
int val; struct semid_ds *buf; unsigned short int *array; struct seminfo *__buf; };
void server(void); //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 safesemctl(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, char *argv[]) {
if ( argc < 2 ) {
server(); } else {
client(atoi(argv[1])); }
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 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(\ while(1) {
printf(\ fflush(stdout);
locksem(semid, SN_FULL); printf(\
printf(\ unlocksem(semid, SN_EMPTY); } }
void client(int shmid) {
int semid; void *shmdata; char *buffer;
shmdata = safeshmat(shmid, 0, 0); semid = *(int *)shmdata;
buffer = shmdata + sizeof(int);
printf(\ while(1) {
char input[3];
printf(\ printf(\
fgets(input, sizeof(input), stdin); switch(input[0]) {
case '1': clientwrite(shmid, semid, buffer); break;
case '2': exit(0); break; } } }
void delete(void) {
printf(\ if (semctl(deleteSemid, 0, IPC_RMID, 0) == -1 ) {
printf(\ } }
void sigdelete(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); }
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(\ fflush(stdout);
locksem(semid, SN_EMPTY); printf(\
printf(\
fgets(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(\ exit(254); }
return retval; }
int safesemctl(int semid, int semnum, int cmd, union semun arg) {
int retval;
if ( (retval=semctl(semid, semnum, cmd, arg)) == -1) {
printf(\ exit(254); }
return retval; }
int safesemop(int semid, struct sembuf *sops, unsigned nsops) {
int retval;
if ( (retval=semop(semid, sops, nsops)) == -1) {
printf(\ exit(254); }
return retval; }
int safeshmget(key_t key, int size, int shmflg) {
int retval;
if ( (retval=shmget(key, size, shmflg)) == -1) {
printf(\ exit(254); }
return retval; }
void *safeshmat(int shmid, const void *shmaddr, int shmflg) {
void *retval;
if ( (retval=shmat(shmid, shmaddr, shmflg)) == (void *)-1) {
printf(\ exit(254); }
return retval; }
int safeshmctl(int shmid, int cmd, struct shmid_ds *buf) {
int retval;
if ( (retval=shmctl(shmid, cmd, buf)) == -1) {
printf(\ exit(254); }
return retval; }
-------------------------------- atexit 语法:
#include
功能： 当程序终止执行时，函数调用函数指针func所指向的函数。可以执行多重调用(至少32个)，这些函数以其注册的倒序执行。执行成功返回零值，失败则返回非零值