In computer networks, the switch device employs circular-bounded buffer (called

Question

In computer networks, the switch device employs circular-bounded

buffer (called shared memory) to store incoming frames before

forwarding it towards its final destination. If there are no frames

to be served, the switch

Explanation / Answer

#include #include #include static struct state { /* Internal record of attached segments. */ int shmid; /* shmid of attached segment */ char *shmaddr; /* attach point */ int shmflg; /* flags used on attach */ } ap[MAXnap]; /* State of current attached segments. */ int nap; /* Number of currently attached segments. */ ... char *addr; /* address work variable */ register int i; /* work area */ register struct state *p; /* ptr to current state entry */ ... p = &ap[nap++]; p->shmid = ... p->shmaddr = ... p->shmflg = ... p->shmaddr = shmat(p->shmid, p->shmaddr, p->shmflg); if(p->shmaddr == (char *)-1) { perror("shmop: shmat failed"); nap--; } else (void) fprintf(stderr, "shmop: shmat returned %#8.8x ", p->shmaddr); ... i = shmdt(addr); if(i == -1) { perror("shmop: shmdt failed"); } else { (void) fprintf(stderr, "shmop: shmdt returned %d ", i); for (p = ap, i = nap; i--; p++) if (p->shmaddr == addr) *p = ap[--nap]; } ...

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