1 /* SPDX-License-Identifier: BSD-3-Clause
2 * Copyright(c) 2010-2014 Intel Corporation
11 * RTE Read-Write Locks
13 * This file defines an API for read-write locks. The lock is used to
14 * protect data that allows multiple readers in parallel, but only
15 * one writer. All readers are blocked until the writer is finished
24 #include <rte_common.h>
25 #include <rte_atomic.h>
26 #include <rte_pause.h>
29 * The rte_rwlock_t type.
31 * cnt is -1 when write lock is held, and > 0 when read locks are held.
34 volatile int32_t cnt; /**< -1 when W lock held, > 0 when R locks held. */
38 * A static rwlock initializer.
40 #define RTE_RWLOCK_INITIALIZER { 0 }
43 * Initialize the rwlock to an unlocked state.
46 * A pointer to the rwlock structure.
49 rte_rwlock_init(rte_rwlock_t *rwl)
55 * Take a read lock. Loop until the lock is held.
58 * A pointer to a rwlock structure.
61 rte_rwlock_read_lock(rte_rwlock_t *rwl)
66 while (success == 0) {
67 x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
68 /* write lock is held */
73 success = __atomic_compare_exchange_n(&rwl->cnt, &x, x + 1, 1,
74 __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
80 * @b EXPERIMENTAL: this API may change without prior notice.
82 * try to take a read lock.
85 * A pointer to a rwlock structure.
87 * - zero if the lock is successfully taken
88 * - -EBUSY if lock could not be acquired for reading because a
89 * writer holds the lock
91 static inline __rte_experimental int
92 rte_rwlock_read_trylock(rte_rwlock_t *rwl)
97 while (success == 0) {
98 x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
99 /* write lock is held */
102 success = __atomic_compare_exchange_n(&rwl->cnt, &x, x + 1, 1,
103 __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
110 * Release a read lock.
113 * A pointer to the rwlock structure.
116 rte_rwlock_read_unlock(rte_rwlock_t *rwl)
118 __atomic_fetch_sub(&rwl->cnt, 1, __ATOMIC_RELEASE);
123 * @b EXPERIMENTAL: this API may change without prior notice.
125 * try to take a write lock.
128 * A pointer to a rwlock structure.
130 * - zero if the lock is successfully taken
131 * - -EBUSY if lock could not be acquired for writing because
132 * it was already locked for reading or writing
134 static inline __rte_experimental int
135 rte_rwlock_write_trylock(rte_rwlock_t *rwl)
139 x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
140 if (x != 0 || __atomic_compare_exchange_n(&rwl->cnt, &x, -1, 1,
141 __ATOMIC_ACQUIRE, __ATOMIC_RELAXED) == 0)
148 * Take a write lock. Loop until the lock is held.
151 * A pointer to a rwlock structure.
154 rte_rwlock_write_lock(rte_rwlock_t *rwl)
159 while (success == 0) {
160 x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
166 success = __atomic_compare_exchange_n(&rwl->cnt, &x, -1, 1,
167 __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
172 * Release a write lock.
175 * A pointer to a rwlock structure.
178 rte_rwlock_write_unlock(rte_rwlock_t *rwl)
180 __atomic_store_n(&rwl->cnt, 0, __ATOMIC_RELEASE);
184 * Try to execute critical section in a hardware memory transaction, if it
185 * fails or not available take a read lock
187 * NOTE: An attempt to perform a HW I/O operation inside a hardware memory
188 * transaction always aborts the transaction since the CPU is not able to
189 * roll-back should the transaction fail. Therefore, hardware transactional
190 * locks are not advised to be used around rte_eth_rx_burst() and
191 * rte_eth_tx_burst() calls.
194 * A pointer to a rwlock structure.
197 rte_rwlock_read_lock_tm(rte_rwlock_t *rwl);
200 * Commit hardware memory transaction or release the read lock if the lock is used as a fall-back
203 * A pointer to the rwlock structure.
206 rte_rwlock_read_unlock_tm(rte_rwlock_t *rwl);
209 * Try to execute critical section in a hardware memory transaction, if it
210 * fails or not available take a write lock
212 * NOTE: An attempt to perform a HW I/O operation inside a hardware memory
213 * transaction always aborts the transaction since the CPU is not able to
214 * roll-back should the transaction fail. Therefore, hardware transactional
215 * locks are not advised to be used around rte_eth_rx_burst() and
216 * rte_eth_tx_burst() calls.
219 * A pointer to a rwlock structure.
222 rte_rwlock_write_lock_tm(rte_rwlock_t *rwl);
225 * Commit hardware memory transaction or release the write lock if the lock is used as a fall-back
228 * A pointer to a rwlock structure.
231 rte_rwlock_write_unlock_tm(rte_rwlock_t *rwl);
237 #endif /* _RTE_RWLOCK_H_ */