共享記憶體多程序間通訊，程序間同步使用訊號量來實現
阿新 • • 發佈：2019-01-04
Linux 環境下C程式設計指南，通過共享記憶體進行程序間通訊的例子，程序間同步使用訊號量來實現。
程式碼 11-5
使用說明：這是一個簡單的伺服器和客戶端程式，如果啟動程式時不帶引數，則執行伺服器程式；
如果帶引數，則執行客戶端程式，所帶引數只有一個，就是伺服器端所顯示的共享記憶體的引用ID。
實現原理：伺服器端啟動後，建立訊號量和共享記憶體，並將共享記憶體的引用ID顯示出來，將訊號量
的引用ID存放在共享記憶體中。客戶端啟動後，利用伺服器端提供的記憶體共享ID將共享記憶體附加到地址段，
讀取訊號量以實現兩個程序之間的同步。之後，這兩個程序就可以利用共享記憶體進行程序間通訊，客戶
端輸入的資訊將在伺服器端顯示出來。
#include <stdlib.h> #include <errno.h> #include <string.h> #include <signal.h> #include <stdio.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/sem.h> #include <sys/shm.h> #define SHMDATASIZE 1000 #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); 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; //1 建立訊號量燈semget(key, nsems, semflg) semid = safesemget(IPC_PRIVATE, 2, SHM_R|SHM_W); deleteSemid = semid; //2 當程式終止執行時，執行刪除訊號量，semctl(deleteSemid, 0, IPC_RMID, 0) atexit(&delete); //3 接收到訊號 SIGINT 則執行 sigdelete 函式 exit(0) signal(SIGINT, &sigdelete); //4 設定兩個訊號燈，空與滿，val =1 semctl(semid, semnum, cmd, arg) sunion.val = 1; safesemctl(semid, SN_EMPTY, SETVAL, sunion); sunion.val = 0; safesemctl(semid, SN_FULL, SETVAL, sunion); //5 建立共享記憶體 shmid = safeshmget(IPC_PRIVATE, SHMDATASIZE, IPC_CREAT|SHM_R|SHM_W); //6 將共享記憶體載入到自己的地址空間,shmdata為對映區的其始地址 shmdata = safeshmat(shmid, 0, 0); //7 刪除共享記憶體，當所有附加該共享記憶體的程序結束或斷開與該共享記憶體的連線時才執行 safeshmctl(shmid, IPC_RMID, NULL); //8 共享記憶體首地址為訊號燈id *(int *)shmdata = semid; //buffer指向共享記憶體+四個位元組後 buffer = shmdata + sizeof(int); printf("Server is running with SHM id ** %d **/n", shmid); while(1) { printf("Waiting until full..."); fflush(stdout); //申請1個訊號燈資源，使訊號燈1阻塞 locksem(semid, SN_FULL); printf("done./n"); printf("Message received: %s./n", buffer); //釋放1個訊號燈資源， unlocksem(semid, SN_EMPTY); } } void client(int shmid) { int semid; void *shmdata; char *buffer; //1 程序載入共享記憶體到自己地址空間 shmdata = safeshmat(shmid, 0, 0); //2 共享記憶體中第一個int為訊號燈 semid = *(int *)shmdata; //3 共享記憶體指標 buffer = shmdata + sizeof(int); printf("Client operational: shm id is %d, sem id is %d/n", shmid, semid); while(1) { char input[3]; printf("/n/nMenu/n1.send a message/n"); printf("2.Exit/n"); //輸入三個字元 fgets(input, sizeof(input), stdin); switch(input[0]) { 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"); } } //程式退出 void sigdelete(int signum) { exit(0); } //申請訊號燈鎖sb.sem_op = -1;semnum第幾個訊號燈 void locksem(int semid, int semnum) { //sem_op = -1申請一個資源 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("Waiting until empty..."); fflush(stdout); locksem(semid, SN_EMPTY); printf("done./n"); printf("Enter Message: "); fgets(buffer, BUFFERSIZE, stdin); unlocksem(semid, SN_FULL); } //safeshmget 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) { int retval; if ( (retval=semctl(semid, semnum, cmd, arg)) == -1) { printf("semctl error: %s./n", strerror(errno)); exit(254); } return retval; } //訊號燈操作設定 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; } //IPC_PRIVATE, 2, SHM_R|SHM_W /******************************************************************** 函式名稱: safeshmget 函式功能: 從快取中讀取nSize位元組大小的資料到pBuf中 計算到快取尾還能讀出快取位元組數，如果尾部大小夠讀，則從尾部直 接讀出，否則，則先從快取尾讀，再從快取頭讀取 輸入引數: No 輸出引數: No 輸入輸出: No 返回引數: No *******************************************************************/ 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; } //將共享記憶體載入到自己的地址空間 void *safeshmat(int shmid, const void *shmaddr, int shmflg) { void *retval; if ( (retval=shmat(shmid, shmaddr, shmflg)) == (void *)-1) { printf("shmat error: %s./n", strerror(errno)); exit(254); } return retval; } int safeshmctl(int shmid, int cmd, struct shmid_ds *buf) { int retval; if ( (retval=shmctl(shmid, cmd, buf)) == -1) { printf("shmctl error: %s./n", strerror(errno)); exit(254); } return retval; } -------------------------------- atexit 語法: #include <stdlib.h> int atexit( void (*func)(void) );
功能： 當程式終止執行時，函式呼叫函式指標func所指向的函式。可以執行多重呼叫(至少32個)，這些函式以其註冊的倒序執行。執行成功返回零值，失敗則返回非零值。