The Linux Programming Interface: a linux and unix system Programming Handbook
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Listing 46-6: Displaying all System V message queues on the system ––––––––––––––––––––––––––––––––––––––––––––––––––––––––– svmsg/svmsg_ls.c #define _GNU_SOURCE #include #include #include "tlpi_hdr.h" int main(int argc, char *argv[]) { int maxind, ind, msqid; struct msqid_ds ds; struct msginfo msginfo; /* Obtain size of kernel 'entries' array */ maxind = msgctl(0, MSG_INFO, (struct msqid_ds *) &msginfo); if (maxind == -1) errExit("msgctl-MSG_INFO"); printf("maxind: %d\n\n", maxind); printf("index id key messages\n"); /* Retrieve and display information from each element of 'entries' array */ for (ind = 0; ind <= maxind; ind++) { msqid = msgctl(ind, MSG_STAT, &ds); if (msqid == -1) { if (errno != EINVAL && errno != EACCES) errMsg("msgctl-MSG_STAT"); /* Unexpected error */ continue; /* Ignore this item */ } printf("%4d %8d 0x%08lx %7ld\n", ind, msqid, (unsigned long) ds.msg_perm.__key, (long) ds.msg_qnum); } exit(EXIT_SUCCESS); } ––––––––––––––––––––––––––––––––––––––––––––––––––––––––– svmsg/svmsg_ls.c 46.7 Client-Server Programming with Message Queues In this section, we consider two of various possible designs for client-server applica- tions using System V message queues: z The use of a single message queue for exchanging messages in both directions between server and client. z The use of separate message queues for the server and for each client. The server’s queue is used to receive incoming client requests, and responses are sent to clients via the individual client queues. 954 Chapter 46 Which approach we choose depends on the requirements of our application. We next consider some of the factors that may influence our choice. tải về 6.93 Mb. Chia sẻ với bạn bè của bạn:
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