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生产者-消费者问题，也叫做缓存绑定问题(bounded-buffer),是一个多进程同步问题。
- 即有两个进程:制造少和消费者，共享一个固定大小的缓存
- 制造商的工作是制造一段数据，放进缓存，如此重复。
- 消费者一次消费一段数据，从缓存中取出。
- 要保证不让制造商在缓存还是满的时候仍要向内写数据，不让消费者试图从空的缓存中取出数据。
#include#include #include #include #include #include #include #include #include "ipc.h"int main ( int argc , char * argv[] ){ int i,producer_pid,consumer_pid,item,shmid; semaphore mutex,empty,full;//定义互斥量mutex,定义信号量empty,full; union semun sem_union; void* shared_memory = (void*)0; struct shared_use_st * shared_stuff; /* int semget ( key_t key , int num_sems , int sem_flags ); 1.第一个参数key是一个用来允许不相关的进程访问相同信号量的整数值， 所有的信号量信号量是为不同的程序提供一个key来简介访问的, 对于每一个信号量系统生成一个信号量标识符。符号量键值只可以由semget 获得，所有其他的信号量函数所用的信号量标识符都是由semget所返回的。 2.num_sems参数是所需要的信号量数目，这个值通常是1 3.sem_flags参数是一个标记集合 IPC_CREAT与IPC_EXCL的组合来保证我们可以的到一个新的唯一的信号量 如果得不到会报错 4.返回值如果是一个整数，这是用于其他信号量函数的标识符， 如果失败，则会返回-1 */ if ( ( mutex = semget ( (key_t) KEY_MUTEX , 1 , 0666|IPC_CREAT)) == -1 ) { fprintf ( stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if (( empty = semget( (key_t) KEY_EMPTY , 1 , 0666|IPC_CREAT)) == -1 ) { fprintf ( stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if (( full = semget((key_t) KEY_FULL , 1 , 0666|IPC_CREAT)) == -1 ) { fprintf ( stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if ((shmid = shmget ((key_t)KEY_SHM,sizeof (struct shared_use_st),0666|IPC_CREAT))==-1) { fprintf ( stderr , "Failerd to create shared memory!"); exit(EXIT_FAILURE); } sem_union.val = 1; if ( semctl(mutex,0,SETVAL,sem_union) == -1 ) { fprintf ( stderr , "Failed to set semaphore!"); exit(EXIT_FAILURE); } sem_union.val = 0; if ( semctl(full,0,SETVAL,sem_union) == -1 ) { fprintf ( stderr , "Failed to set semaphore!"); exit(EXIT_FAILURE); } sem_union.val = BUFFER_SIZE; if ( semctl(empty, 0 , SETVAL , sem_union) == -1 ) { fprintf ( stderr , "Failed to set semaphore!"); exit(EXIT_FAILURE); } /* void* shmat ( int shmid , const void* shmaddr , int shmflg ) 链接共享内存标识符为shmid的共享内存，链接成功后把共享内存区对象 映射到调用进程的地址空间,随后可像本地空间一样访问。 shmid 共享内存标识符 shmaddr 指定共享内存出现在进程内存地址的什么位置，直接指定为NULL让内核自己决定 一个合适的地址位置. SHM_RDONLY 为只读模式，其他为读写模式 */ if (( shared_memory = shmat( shmid ,(void*)0 , 0)) == (void*)-1 ) { fprintf ( stderr , "shmat failed\n"); exit(EXIT_FAILURE); } shared_stuff = ( struct shared_use_st * ) shared_memory; for ( i = 0; i < BUFFER_SIZE ; i ++ ) { shared_stuff->buffer[i] = 0; } shared_stuff->low = 0; shared_stuff->high = 0; shared_stuff->cur = 0; exit(EXIT_SUCCESS);} /* int shmdt ( const void* shmaddr ) 与shmat相反，是用来断开与共享内存附加点的地址，进制本进程访问瓷片共享内存 shmaddr:链接共享内存的起始地址 成功返回0,除错返回-1 */
#include "ipc.h"int main ( int argc , char * argv[] ){ int i,item,shmid; semaphore mutex,empty,full; union semun sem_union; void* shared_memory = (void*)0; struct shared_use_st *shared_stuff; if ((mutex = semget((key_t)KEY_MUTEX,1,0666|IPC_CREAT)) == -1 ) { fprintf ( stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if ((empty = semget((key_t)KEY_EMPTY,1,0666|IPC_CREAT)) == -1 ) { fprintf ( stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if ((full = semget((key_t)KEY_FULL,1,0666|IPC_CREAT)) == -1 ) { fprintf ( stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if ((shmid=shmget((key_t)KEY_SHM,sizeof(struct shared_use_st),0666|IPC_CREAT)) == -1 ) { fprintf ( stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if ((shared_memory = shmat(shmid,(void*)0,0)) == (void*)-1) { fprintf ( stderr , "shmat failed\n"); exit(EXIT_FAILURE); } shared_stuff = ( struct shared_use_st * ) shared_memory; for ( i = 0 ; i < 30 ; i++ ) { item = ++(shared_stuff->cur); sleep(1); printf ( "Producing item %d\n" , item ); sem_p ( empty );//减少一个空位 sem_p ( mutex );//锁上互斥锁 (shared_stuff->buffer)[(shared_stuff->high)] = item; (shared_stuff->high) = ((shared_stuff->high)+1) % BUFFER_SIZE; printf ( "Inserting item %d\n" , item ); sem_v ( mutex ); sem_v ( full ); } if ( shmdt(shared_memory) == -1 ) { fprintf ( stderr , "shmat failed\n"); exit(EXIT_FAILURE); } printf ( "Finish!\n" ); getchar(); exit(EXIT_SUCCESS);} #include "ipc.h"int main ( int argc , char* argv[] ){ int i,item,shmid; semaphore mutex,empty,full; void* shared_memory = ( void* ) 0; struct shared_use_st* shared_stuff; if ((mutex=semget((key_t)KEY_MUTEX,1,0666|IPC_CREAT)) == -1 ) { fprintf (stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if ((empty=semget((key_t)KEY_EMPTY,1,0666|IPC_CREAT)) == -1 ) { fprintf (stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if ((full=semget((key_t)KEY_FULL,1,0666|IPC_CREAT)) == -1 ) { fprintf (stderr , "Failed to create semaphore!"); exit(EXIT_FAILURE); } if ((shared_memory = shmat(shmid,(void*)0,0) ) ==(void*)-1 ) { fprintf ( stderr , "shmat failed\n"); exit(EXIT_FAILURE); } shared_stuff = (struct shared_use_st*)shared_memory; for(i=0;i<30;i++) { sem_p(full); sem_p(mutex); item = shared_stuff->buffer[shared_stuff->low]; (shared_stuff->buffer)[(shared_stuff->low)]=0; shared_stuff->low = ((shared_stuff->low)+1)%BUFFER_SIZE; printf ( "Removing item %d\n" , item ); sem_v(mutex); sem_v(empty); printf ( "Consuming item %d\n" ,item ); sleep(2); } if ( shmdt(shared_memory) == -1 ) { fprintf ( stderr , "shmat failed\n" ); exit ( EXIT_FAILURE); } printf ( "Finish!\n" ); getchar(); exit(EXIT_SUCCESS);}