Develop a program in C which implements distribution of candies to kids using sp

Question

Develop a program in C which implements distribution of candies to kids using spinlocks. For testing, you can assume 29 candies and invoke five processes as kids. Each kid can take only one candy at a time by decrementing the total number of candies using mutual exclusion. In the end, each kids would display the number of candies obtained. Kids are not allowed to snatch candies from each other.

Explanation / Answer

#if HAVE_CONFIG_H #include #endif #if STANDALONE #include #include #include #include #include #include #include #include #include "tdb.h" #include "spinlock.h" #define DEBUG #else #include "includes.h" #endif #ifdef USE_SPINLOCKS /* * ARCH SPECIFIC */ #if defined(SPARC_SPINLOCKS) static inline int __spin_trylock(spinlock_t *lock) { unsigned int result; asm volatile("ldstub [%1], %0" : "=r" (result) : "r" (lock) : "memory"); return (result == 0) ? 0 : EBUSY; } static inline void __spin_unlock(spinlock_t *lock) { asm volatile("":::"memory"); *lock = 0; } static inline void __spin_lock_init(spinlock_t *lock) { *lock = 0; } static inline int __spin_is_locked(spinlock_t *lock) { return (*lock != 0); } #elif defined(POWERPC_SPINLOCKS) static inline int __spin_trylock(spinlock_t *lock) { unsigned int result; __asm__ __volatile__( "1: lwarx %0,0,%1 cmpwi 0,%0,0 li %0,0 bne- 2f li %0,1 stwcx. %0,0,%1 bne- 1b isync 2:" : "=&r"(result) : "r"(lock) : "cr0", "memory"); return (result == 1) ? 0 : EBUSY; } static inline void __spin_unlock(spinlock_t *lock) { asm volatile("eieio":::"memory"); *lock = 0; } static inline void __spin_lock_init(spinlock_t *lock) { *lock = 0; } static inline int __spin_is_locked(spinlock_t *lock) { return (*lock != 0); } #elif defined(INTEL_SPINLOCKS) static inline int __spin_trylock(spinlock_t *lock) { int oldval; asm volatile("xchgl %0,%1" : "=r" (oldval), "=m" (*lock) : "0" (0) : "memory"); return oldval > 0 ? 0 : EBUSY; } static inline void __spin_unlock(spinlock_t *lock) { asm volatile("":::"memory"); *lock = 1; } static inline void __spin_lock_init(spinlock_t *lock) { *lock = 1; } static inline int __spin_is_locked(spinlock_t *lock) { return (*lock != 1); } #elif defined(MIPS_SPINLOCKS) static inline unsigned int load_linked(unsigned long addr) { unsigned int res; __asm__ __volatile__("ll %0,(%1)" : "=r" (res) : "r" (addr)); return res; } static inline unsigned int store_conditional(unsigned long addr, unsigned int value) { unsigned int res; __asm__ __volatile__("sc %0,(%2)" : "=r" (res) : "0" (value), "r" (addr)); return res; } static inline int __spin_trylock(spinlock_t *lock) { unsigned int mw; do { mw = load_linked(lock); if (mw) return EBUSY; } while (!store_conditional(lock, 1)); asm volatile("":::"memory"); return 0; } static inline void __spin_unlock(spinlock_t *lock) { asm volatile("":::"memory"); *lock = 0; } static inline void __spin_lock_init(spinlock_t *lock) { *lock = 0; } static inline int __spin_is_locked(spinlock_t *lock) { return (*lock != 0); } #else #error Need to implement spinlock code in spinlock.c #endif /* * OS SPECIFIC */ static void yield_cpu(void) { struct timespec tm; #ifdef USE_SCHED_YIELD sched_yield(); #else /* Linux will busy loop for delays < 2ms on real time tasks */ tm.tv_sec = 0; tm.tv_nsec = 2000000L + 1; nanosleep(&tm, NULL); #endif } static int this_is_smp(void) { return 0; } /* * GENERIC */ static int smp_machine = 0; static inline void __spin_lock(spinlock_t *lock) { int ntries = 0; while(__spin_trylock(lock)) { while(__spin_is_locked(lock)) { if (smp_machine && ntries++ lock); if (!(rwlock->count & RWLOCK_BIAS)) { rwlock->count++; __spin_unlock(&rwlock->lock); return; } __spin_unlock(&rwlock->lock); while(rwlock->count & RWLOCK_BIAS) { if (smp_machine && ntries++ lock); if (rwlock->count == 0) { rwlock->count |= RWLOCK_BIAS; __spin_unlock(&rwlock->lock); return; } __spin_unlock(&rwlock->lock); while(rwlock->count != 0) { if (smp_machine && ntries++ lock); #ifdef DEBUG if (!(rwlock->count & RWLOCK_BIAS)) fprintf(stderr, "bug: write_unlock "); #endif rwlock->count &= ~RWLOCK_BIAS; __spin_unlock(&rwlock->lock); } static void __read_unlock(tdb_rwlock_t *rwlock) { __spin_lock(&rwlock->lock); #ifdef DEBUG if (!rwlock->count) fprintf(stderr, "bug: read_unlock "); if (rwlock->count & RWLOCK_BIAS) fprintf(stderr, "bug: read_unlock "); #endif rwlock->count--; __spin_unlock(&rwlock->lock); } /* TDB SPECIFIC */ /* lock a list in the database. list -1 is the alloc list */ int tdb_spinlock(TDB_CONTEXT *tdb, int list, int rw_type) { tdb_rwlock_t *rwlocks; if (!tdb->map_ptr) return -1; rwlocks = (tdb_rwlock_t *)((char *)tdb->map_ptr + tdb->header.rwlocks); switch(rw_type) { case F_RDLCK: __read_lock(&rwlocks[list+1]); break; case F_WRLCK: __write_lock(&rwlocks[list+1]); break; default: return TDB_ERRCODE(TDB_ERR_LOCK, -1); } return 0; } /* unlock the database. */ int tdb_spinunlock(TDB_CONTEXT *tdb, int list, int rw_type) { tdb_rwlock_t *rwlocks; if (!tdb->map_ptr) return -1; rwlocks = (tdb_rwlock_t *)((char *)tdb->map_ptr + tdb->header.rwlocks); switch(rw_type) { case F_RDLCK: __read_unlock(&rwlocks[list+1]); break; case F_WRLCK: __write_unlock(&rwlocks[list+1]); break; default: return TDB_ERRCODE(TDB_ERR_LOCK, -1); } return 0; } int tdb_create_rwlocks(int fd, unsigned int hash_size) { unsigned size, i; tdb_rwlock_t *rwlocks; size = (hash_size + 1) * sizeof(tdb_rwlock_t); rwlocks = malloc(size); if (!rwlocks) return -1; for(i = 0; i header.rwlocks == 0) return 0; if (!tdb->map_ptr) return -1; /* We're mmapped here */ rwlocks = (tdb_rwlock_t *)((char *)tdb->map_ptr + tdb->header.rwlocks); for(i = 0; i header.hash_size+1; i++) { __spin_lock_init(&rwlocks[i].lock); rwlocks[i].count = 0; } return 0; } #else int tdb_create_rwlocks(int fd, unsigned int hash_size) { return 0; } int tdb_spinlock(TDB_CONTEXT *tdb, int list, int rw_type) { return -1; } int tdb_spinunlock(TDB_CONTEXT *tdb, int list, int rw_type) { return -1; } /* Non-spinlock version: remove spinlock pointer */ int tdb_clear_spinlocks(TDB_CONTEXT *tdb) { tdb_off off = (tdb_off)((char *)&tdb->header.rwlocks - (char *)&tdb->header); tdb->header.rwlocks = 0; if (lseek(tdb->fd, off, SEEK_SET) != off || write(tdb->fd, (void *)&tdb->header.rwlocks, sizeof(tdb->header.rwlocks)) != sizeof(tdb->header.rwlocks)) return -1; return 0; } #endif

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