进程间通信的例子-共享内存

haoningabc

消费者
root@ubuntu:~/test/SourceCode/ch14# cat shm1.c /* Our first program is a consumer. After the headers the shared memory segment (the size of our shared memory structure) is created with a call to shmget, with the IPC_CREAT bit specified. */#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <sys/shm.h>#include "shm_com.h"int main(){    int running = 1;    void *shared_memory = (void *)0;    struct shared_use_st *shared_stuff;    int shmid;    srand((unsigned int)getpid());        shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666 | IPC_CREAT);    if (shmid == -1) {        fprintf(stderr, "shmget failed\n");        exit(EXIT_FAILURE);    }/* We now make the shared memory accessible to the program. */    shared_memory = shmat(shmid, (void *)0, 0);    if (shared_memory == (void *)-1) {        fprintf(stderr, "shmat failed\n");        exit(EXIT_FAILURE);    }    printf("Memory attached at %X\n", (int)shared_memory);/* The next portion of the program assigns the shared_memory segment to shared_stuff, which then prints out any text in written_by_you. The loop continues until end is found in written_by_you. The call to sleep forces the consumer to sit in its critical section, which makes the producer wait. */    shared_stuff = (struct shared_use_st *)shared_memory;    shared_stuff->written_by_you = 0;    while(running) {        if (shared_stuff->written_by_you) {            printf("You wrote: %s", shared_stuff->some_text);            sleep( rand() % 4 ); /* make the other process wait for us ! */            shared_stuff->written_by_you = 0;            if (strncmp(shared_stuff->some_text, "end", 3) == 0) {                running = 0;            }        }    }/* Lastly, the shared memory is detached and then deleted. */    if (shmdt(shared_memory) == -1) {        fprintf(stderr, "shmdt failed\n");        exit(EXIT_FAILURE);    }    if (shmctl(shmid, IPC_RMID, 0) == -1) {        fprintf(stderr, "shmctl(IPC_RMID) failed\n");        exit(EXIT_FAILURE);    }    exit(EXIT_SUCCESS);}root@ubuntu:~/test/SourceCode/ch14#

root@ubuntu:~/test/SourceCode/ch14# cat shm_com.h /* A common header file to describe the shared memory we wish to pass about. */#define TEXT_SZ 2048struct shared_use_st {    int written_by_you;    char some_text[TEXT_SZ];};

生产者
root@ubuntu:~/test/SourceCode/ch14# cat shm2.c /* The second program is the producer and allows us to enter data for consumers. It's very similar to shm1.c and looks like this. */#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <sys/shm.h>#include "shm_com.h"int main(){    int running = 1;    void *shared_memory = (void *)0;    struct shared_use_st *shared_stuff;    char buffer[BUFSIZ];    int shmid;    shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666 | IPC_CREAT);    if (shmid == -1) {        fprintf(stderr, "shmget failed\n");        exit(EXIT_FAILURE);    }    shared_memory = shmat(shmid, (void *)0, 0);    if (shared_memory == (void *)-1) {        fprintf(stderr, "shmat failed\n");        exit(EXIT_FAILURE);    }    printf("Memory attached at %X\n", (int)shared_memory);    shared_stuff = (struct shared_use_st *)shared_memory;    while(running) {        while(shared_stuff->written_by_you == 1) {            sleep(1);                        printf("waiting for client...\n");        }        printf("Enter some text: ");        fgets(buffer, BUFSIZ, stdin);                strncpy(shared_stuff->some_text, buffer, TEXT_SZ);        shared_stuff->written_by_you = 1;        if (strncmp(buffer, "end", 3) == 0) {                running = 0;        }    }    if (shmdt(shared_memory) == -1) {        fprintf(stderr, "shmdt failed\n");        exit(EXIT_FAILURE);    }    exit(EXIT_SUCCESS);}root@ubuntu:~/test/SourceCode/ch14#




结果为


说明：使用一个结构，标识written_by_you
当共享内存写入时就设置这个标志，，这个标志被设置时，程序就从共享内存中读取文本