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/* SPDX-License-Identifier: BSD-3-Clause
* Copyright(c) 2010-2014 Intel Corporation
*/
#ifndef _RTE_RWLOCK_H_
#define _RTE_RWLOCK_H_
/**
* @file
*
* RTE Read-Write Locks
*
* This file defines an API for read-write locks. The lock is used to
* protect data that allows multiple readers in parallel, but only
* one writer. All readers are blocked until the writer is finished
* writing.
*
*/
#ifdef __cplusplus
extern "C" {
#endif
#include <rte_common.h>
#include <rte_atomic.h>
#include <rte_pause.h>
/**
* The rte_rwlock_t type.
*
* cnt is -1 when write lock is held, and > 0 when read locks are held.
*/
typedef struct {
volatile int32_t cnt; /**< -1 when W lock held, > 0 when R locks held. */
} rte_rwlock_t;
/**
* A static rwlock initializer.
*/
#define RTE_RWLOCK_INITIALIZER { 0 }
/**
* Initialize the rwlock to an unlocked state.
*
* @param rwl
* A pointer to the rwlock structure.
*/
static inline void
rte_rwlock_init(rte_rwlock_t *rwl)
{
rwl->cnt = 0;
}
/**
* Take a read lock. Loop until the lock is held.
*
* @param rwl
* A pointer to a rwlock structure.
*/
static inline void
rte_rwlock_read_lock(rte_rwlock_t *rwl)
{
int32_t x;
int success = 0;
while (success == 0) {
x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
/* write lock is held */
if (x < 0) {
rte_pause();
continue;
}
success = __atomic_compare_exchange_n(&rwl->cnt, &x, x + 1, 1,
__ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
}
}
/**
* Release a read lock.
*
* @param rwl
* A pointer to the rwlock structure.
*/
static inline void
rte_rwlock_read_unlock(rte_rwlock_t *rwl)
{
__atomic_fetch_sub(&rwl->cnt, 1, __ATOMIC_RELEASE);
}
/**
* Take a write lock. Loop until the lock is held.
*
* @param rwl
* A pointer to a rwlock structure.
*/
static inline void
rte_rwlock_write_lock(rte_rwlock_t *rwl)
{
int32_t x;
int success = 0;
while (success == 0) {
x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
/* a lock is held */
if (x != 0) {
rte_pause();
continue;
}
success = __atomic_compare_exchange_n(&rwl->cnt, &x, -1, 1,
__ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
}
}
/**
* Release a write lock.
*
* @param rwl
* A pointer to a rwlock structure.
*/
static inline void
rte_rwlock_write_unlock(rte_rwlock_t *rwl)
{
__atomic_store_n(&rwl->cnt, 0, __ATOMIC_RELEASE);
}
/**
* Try to execute critical section in a hardware memory transaction, if it
* fails or not available take a read lock
*
* NOTE: An attempt to perform a HW I/O operation inside a hardware memory
* transaction always aborts the transaction since the CPU is not able to
* roll-back should the transaction fail. Therefore, hardware transactional
* locks are not advised to be used around rte_eth_rx_burst() and
* rte_eth_tx_burst() calls.
*
* @param rwl
* A pointer to a rwlock structure.
*/
static inline void
rte_rwlock_read_lock_tm(rte_rwlock_t *rwl);
/**
* Commit hardware memory transaction or release the read lock if the lock is used as a fall-back
*
* @param rwl
* A pointer to the rwlock structure.
*/
static inline void
rte_rwlock_read_unlock_tm(rte_rwlock_t *rwl);
/**
* Try to execute critical section in a hardware memory transaction, if it
* fails or not available take a write lock
*
* NOTE: An attempt to perform a HW I/O operation inside a hardware memory
* transaction always aborts the transaction since the CPU is not able to
* roll-back should the transaction fail. Therefore, hardware transactional
* locks are not advised to be used around rte_eth_rx_burst() and
* rte_eth_tx_burst() calls.
*
* @param rwl
* A pointer to a rwlock structure.
*/
static inline void
rte_rwlock_write_lock_tm(rte_rwlock_t *rwl);
/**
* Commit hardware memory transaction or release the write lock if the lock is used as a fall-back
*
* @param rwl
* A pointer to a rwlock structure.
*/
static inline void
rte_rwlock_write_unlock_tm(rte_rwlock_t *rwl);
#ifdef __cplusplus
}
#endif
#endif /* _RTE_RWLOCK_H_ */
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