ceph/src/spdk/dpdk/lib/librte_eal/common/include/generic/rte_rwlock.h

   1 /* SPDX-License-Identifier: BSD-3-Clause
   2  * Copyright(c) 2010-2014 Intel Corporation
   3  */
   4
   5 #ifndef _RTE_RWLOCK_H_
   6 #define _RTE_RWLOCK_H_
   7
   8 /**
   9  * @file
  10  *
  11  * RTE Read-Write Locks
  12  *
  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
  16  * writing.
  17  *
  18  */
  19
  20 #ifdef __cplusplus
  21 extern "C" {
  22 #endif
  23
  24 #include <rte_common.h>
  25 #include <rte_atomic.h>
  26 #include <rte_pause.h>
  27
  28 /**
  29  * The rte_rwlock_t type.
  30  *
  31  * cnt is -1 when write lock is held, and > 0 when read locks are held.
  32  */
  33 typedef struct {
  34         volatile int32_t cnt; /**< -1 when W lock held, > 0 when R locks held. */
  35 } rte_rwlock_t;
  36
  37 /**
  38  * A static rwlock initializer.
  39  */
  40 #define RTE_RWLOCK_INITIALIZER { 0 }
  41
  42 /**
  43  * Initialize the rwlock to an unlocked state.
  44  *
  45  * @param rwl
  46  *   A pointer to the rwlock structure.
  47  */
  48 static inline void
  49 rte_rwlock_init(rte_rwlock_t *rwl)
  50 {
  51         rwl->cnt = 0;
  52 }
  53
  54 /**
  55  * Take a read lock. Loop until the lock is held.
  56  *
  57  * @param rwl
  58  *   A pointer to a rwlock structure.
  59  */
  60 static inline void
  61 rte_rwlock_read_lock(rte_rwlock_t *rwl)
  62 {
  63         int32_t x;
  64         int success = 0;
  65
  66         while (success == 0) {
  67                 x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
  68                 /* write lock is held */
  69                 if (x < 0) {
  70                         rte_pause();
  71                         continue;
  72                 }
  73                 success = __atomic_compare_exchange_n(&rwl->cnt, &x, x + 1, 1,
  74                                         __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
  75         }
  76 }
  77
  78 /**
  79  * @warning
  80  * @b EXPERIMENTAL: this API may change without prior notice.
  81  *
  82  * try to take a read lock.
  83  *
  84  * @param rwl
  85  *   A pointer to a rwlock structure.
  86  * @return
  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
  90  */
  91 static inline __rte_experimental int
  92 rte_rwlock_read_trylock(rte_rwlock_t *rwl)
  93 {
  94         int32_t x;
  95         int success = 0;
  96
  97         while (success == 0) {
  98                 x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
  99                 /* write lock is held */
 100                 if (x < 0)
 101                         return -EBUSY;
 102                 success = __atomic_compare_exchange_n(&rwl->cnt, &x, x + 1, 1,
 103                                         __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
 104         }
 105
 106         return 0;
 107 }
 108
 109 /**
 110  * Release a read lock.
 111  *
 112  * @param rwl
 113  *   A pointer to the rwlock structure.
 114  */
 115 static inline void
 116 rte_rwlock_read_unlock(rte_rwlock_t *rwl)
 117 {
 118         __atomic_fetch_sub(&rwl->cnt, 1, __ATOMIC_RELEASE);
 119 }
 120
 121 /**
 122  * @warning
 123  * @b EXPERIMENTAL: this API may change without prior notice.
 124  *
 125  * try to take a write lock.
 126  *
 127  * @param rwl
 128  *   A pointer to a rwlock structure.
 129  * @return
 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
 133  */
 134 static inline __rte_experimental int
 135 rte_rwlock_write_trylock(rte_rwlock_t *rwl)
 136 {
 137         int32_t x;
 138
 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)
 142                 return -EBUSY;
 143
 144         return 0;
 145 }
 146
 147 /**
 148  * Take a write lock. Loop until the lock is held.
 149  *
 150  * @param rwl
 151  *   A pointer to a rwlock structure.
 152  */
 153 static inline void
 154 rte_rwlock_write_lock(rte_rwlock_t *rwl)
 155 {
 156         int32_t x;
 157         int success = 0;
 158
 159         while (success == 0) {
 160                 x = __atomic_load_n(&rwl->cnt, __ATOMIC_RELAXED);
 161                 /* a lock is held */
 162                 if (x != 0) {
 163                         rte_pause();
 164                         continue;
 165                 }
 166                 success = __atomic_compare_exchange_n(&rwl->cnt, &x, -1, 1,
 167                                         __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
 168         }
 169 }
 170
 171 /**
 172  * Release a write lock.
 173  *
 174  * @param rwl
 175  *   A pointer to a rwlock structure.
 176  */
 177 static inline void
 178 rte_rwlock_write_unlock(rte_rwlock_t *rwl)
 179 {
 180         __atomic_store_n(&rwl->cnt, 0, __ATOMIC_RELEASE);
 181 }
 182
 183 /**
 184  * Try to execute critical section in a hardware memory transaction, if it
 185  * fails or not available take a read lock
 186  *
 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.
 192  *
 193  * @param rwl
 194  *   A pointer to a rwlock structure.
 195  */
 196 static inline void
 197 rte_rwlock_read_lock_tm(rte_rwlock_t *rwl);
 198
 199 /**
 200  * Commit hardware memory transaction or release the read lock if the lock is used as a fall-back
 201  *
 202  * @param rwl
 203  *   A pointer to the rwlock structure.
 204  */
 205 static inline void
 206 rte_rwlock_read_unlock_tm(rte_rwlock_t *rwl);
 207
 208 /**
 209  * Try to execute critical section in a hardware memory transaction, if it
 210  * fails or not available take a write lock
 211  *
 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.
 217  *
 218  * @param rwl
 219  *   A pointer to a rwlock structure.
 220  */
 221 static inline void
 222 rte_rwlock_write_lock_tm(rte_rwlock_t *rwl);
 223
 224 /**
 225  * Commit hardware memory transaction or release the write lock if the lock is used as a fall-back
 226  *
 227  * @param rwl
 228  *   A pointer to a rwlock structure.
 229  */
 230 static inline void
 231 rte_rwlock_write_unlock_tm(rte_rwlock_t *rwl);
 232
 233 #ifdef __cplusplus
 234 }
 235 #endif
 236
 237 #endif /* _RTE_RWLOCK_H_ */