进程间通信的例子-共享内存
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;};
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; 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#
http://dl.iteye.com/upload/attachment/0072/5365/21246c4a-b248-3034-b4ff-2bbbd1288f9e.jpg
结果为
http://dl.iteye.com/upload/attachment/0072/5380/1c23194e-2e99-3e51-ab3d-2d720e268dd3.jpg
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
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