// test2.cpp

 #include <pthread.h>

 #include <assert.h>

 // -------------------

 int cpu_thread1 = ;

 int cpu_thread2 = ;

 volatile int x, y, r1, r2;

 void start()

 {

     x = y = r1 = r2 = ;

 }

 void end()

 {

     assert(!(r1 ==  && r2 == ));

 }

 void run1()

 {

     x = ;

     r1 = y;

 }

 void run2()

 {

     y = ;

     r2 = x;

 }

 // -------------------

 static pthread_barrier_t barrier_start;

 static pthread_barrier_t barrier_end;

 static void* thread1(void*)

 {

     while () {

         pthread_barrier_wait(&barrier_start);

         run1();

         pthread_barrier_wait(&barrier_end);

     }

     return NULL;

 }

 static void* thread2(void*)

 {

     while () {

         pthread_barrier_wait(&barrier_start);

         run2();

         pthread_barrier_wait(&barrier_end);

     }

     return NULL;

 }

 int main()

 {

     assert(pthread_barrier_init(&barrier_start, NULL, ) == );

     assert(pthread_barrier_init(&barrier_end, NULL, ) == );

     pthread_t t1;

     pthread_t t2;

     assert(pthread_create(&t1, NULL, thread1, NULL) == );

     assert(pthread_create(&t2, NULL, thread2, NULL) == );

     cpu_set_t cs;

     CPU_ZERO(&cs);

     CPU_SET(cpu_thread1, &cs);

     assert(pthread_setaffinity_np(t1, sizeof(cs), &cs) == );

     CPU_ZERO(&cs);

     CPU_SET(cpu_thread2, &cs);

     assert(pthread_setaffinity_np(t2, sizeof(cs), &cs) == );

     while () {

         start();

         pthread_barrier_wait(&barrier_start);

         pthread_barrier_wait(&barrier_end);

         end();

     }

     return ;

 } 

 /*

 * A simple kernel FIFO implementation.

 *

 * Copyright (C) 2004 Stelian Pop <stelian@popies.net>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

 *

 */

 #include <linux/kernel.h>

 #include <linux/module.h>

 #include <linux/slab.h>

 #include <linux/err.h>

 #include <linux/kfifo.h>

 #include <linux/log2.h>

 /**

 * kfifo_init - allocates a new FIFO using a preallocated buffer

 * @buffer: the preallocated buffer to be used.

 * @size: the size of the internal buffer, this have to be a power of 2.

 * @gfp_mask: get_free_pages mask, passed to kmalloc()

 * @lock: the lock to be used to protect the fifo buffer

 *

 * Do NOT pass the kfifo to kfifo_free() after use! Simply free the

 * &struct kfifo with kfree().

 */

 struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size,

 gfp_t gfp_mask, spinlock_t *lock)

 {

     struct kfifo *fifo;

     /* size must be a power of 2 */

     BUG_ON(!is_power_of_2(size));

     fifo = kmalloc(sizeof(struct kfifo), gfp_mask);

     if (!fifo)

         return ERR_PTR(-ENOMEM);

     fifo->buffer = buffer;

     fifo->size = size;

     fifo->in = fifo->out = ;

     fifo->lock = lock;

     return fifo;

 }

 EXPORT_SYMBOL(kfifo_init);

 /**

 * kfifo_alloc - allocates a new FIFO and its internal buffer

 * @size: the size of the internal buffer to be allocated.

 * @gfp_mask: get_free_pages mask, passed to kmalloc()

 * @lock: the lock to be used to protect the fifo buffer

 *

 * The size will be rounded-up to a power of 2.

 */

 struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask, spinlock_t *lock)

 {

     unsigned char *buffer;

     struct kfifo *ret;

     /*

     * round up to the next power of 2, since our 'let the indices

     * wrap' technique works only in this case.

     */

     if (!is_power_of_2(size)) {

         BUG_ON(size > 0x80000000);

         size = roundup_pow_of_two(size);

     }

     buffer = kmalloc(size, gfp_mask);

     if (!buffer)

         return ERR_PTR(-ENOMEM);

     ret = kfifo_init(buffer, size, gfp_mask, lock);

     if (IS_ERR(ret))

         kfree(buffer);

     return ret;

 }

 EXPORT_SYMBOL(kfifo_alloc);

 /**

 * kfifo_free - frees the FIFO

 * @fifo: the fifo to be freed.

 */

 void kfifo_free(struct kfifo *fifo)

 {

     kfree(fifo->buffer);

     kfree(fifo);

 }

 EXPORT_SYMBOL(kfifo_free);

 /**

 * __kfifo_put - puts some data into the FIFO, no locking version

 * @fifo: the fifo to be used.

 * @buffer: the data to be added.

 * @len: the length of the data to be added.

 *

 * This function copies at most @len bytes from the @buffer into

 * the FIFO depending on the free space, and returns the number of

 * bytes copied.

 *

 * Note that with only one concurrent reader and one concurrent

 * writer, you don't need extra locking to use these functions.

 */

 unsigned int __kfifo_put(struct kfifo *fifo,

 const unsigned char *buffer, unsigned int len)

 {

     unsigned int l;

     len = min(len, fifo->size - fifo->in + fifo->out);

     /*

     * Ensure that we sample the fifo->out index -before- we

     * start putting bytes into the kfifo.

     */

     smp_mb();

     /* first put the data starting from fifo->in to buffer end */

     l = min(len, fifo->size - (fifo->in & (fifo->size - )));

     memcpy(fifo->buffer + (fifo->in & (fifo->size - )), buffer, l);

     /* then put the rest (if any) at the beginning of the buffer */

     memcpy(fifo->buffer, buffer + l, len - l);

     /*

     * Ensure that we add the bytes to the kfifo -before-

     * we update the fifo->in index.

     */

     smp_wmb();

     fifo->in += len;

     return len;

 }

 EXPORT_SYMBOL(__kfifo_put);

 /**

 * __kfifo_get - gets some data from the FIFO, no locking version

 * @fifo: the fifo to be used.

 * @buffer: where the data must be copied.

 * @len: the size of the destination buffer.

 *

 * This function copies at most @len bytes from the FIFO into the

 * @buffer and returns the number of copied bytes.

 *

 * Note that with only one concurrent reader and one concurrent

 * writer, you don't need extra locking to use these functions.

 */

 unsigned int __kfifo_get(struct kfifo *fifo,

 unsigned char *buffer, unsigned int len)

 {

     unsigned int l;

     len = min(len, fifo->in - fifo->out);

     /*

     * Ensure that we sample the fifo->in index -before- we

     * start removing bytes from the kfifo.

     */

     smp_rmb();

     /* first get the data from fifo->out until the end of the buffer */

     l = min(len, fifo->size - (fifo->out & (fifo->size - )));

     memcpy(buffer, fifo->buffer + (fifo->out & (fifo->size - )), l);

     /* then get the rest (if any) from the beginning of the buffer */

     memcpy(buffer + l, fifo->buffer, len - l);

     /*

     * Ensure that we remove the bytes from the kfifo -before-

     * we update the fifo->out index.

     */

     smp_mb();

     fifo->out += len;

     return len;

 }

 EXPORT_SYMBOL(__kfifo_get);