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

   1 /*-
   2  *   BSD LICENSE
   3  *
   4  *   Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
   5  *   All rights reserved.
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   7  *   Redistribution and use in source and binary forms, with or without
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  12  *       notice, this list of conditions and the following disclaimer.
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  14  *       notice, this list of conditions and the following disclaimer in
  15  *       the documentation and/or other materials provided with the
  16  *       distribution.
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  19  *       from this software without specific prior written permission.
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  21  *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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  23  *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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  31  *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  32  */
  33
  34 #ifndef _RTE_RWLOCK_H_
  35 #define _RTE_RWLOCK_H_
  36
  37 /**
  38  * @file
  39  *
  40  * RTE Read-Write Locks
  41  *
  42  * This file defines an API for read-write locks. The lock is used to
  43  * protect data that allows multiple readers in parallel, but only
  44  * one writer. All readers are blocked until the writer is finished
  45  * writing.
  46  *
  47  */
  48
  49 #ifdef __cplusplus
  50 extern "C" {
  51 #endif
  52
  53 #include <rte_common.h>
  54 #include <rte_atomic.h>
  55
  56 /**
  57  * The rte_rwlock_t type.
  58  *
  59  * cnt is -1 when write lock is held, and > 0 when read locks are held.
  60  */
  61 typedef struct {
  62         volatile int32_t cnt; /**< -1 when W lock held, > 0 when R locks held. */
  63 } rte_rwlock_t;
  64
  65 /**
  66  * A static rwlock initializer.
  67  */
  68 #define RTE_RWLOCK_INITIALIZER { 0 }
  69
  70 /**
  71  * Initialize the rwlock to an unlocked state.
  72  *
  73  * @param rwl
  74  *   A pointer to the rwlock structure.
  75  */
  76 static inline void
  77 rte_rwlock_init(rte_rwlock_t *rwl)
  78 {
  79         rwl->cnt = 0;
  80 }
  81
  82 /**
  83  * Take a read lock. Loop until the lock is held.
  84  *
  85  * @param rwl
  86  *   A pointer to a rwlock structure.
  87  */
  88 static inline void
  89 rte_rwlock_read_lock(rte_rwlock_t *rwl)
  90 {
  91         int32_t x;
  92         int success = 0;
  93
  94         while (success == 0) {
  95                 x = rwl->cnt;
  96                 /* write lock is held */
  97                 if (x < 0) {
  98                         rte_pause();
  99                         continue;
 100                 }
 101                 success = rte_atomic32_cmpset((volatile uint32_t *)&rwl->cnt,
 102                                               x, x + 1);
 103         }
 104 }
 105
 106 /**
 107  * Release a read lock.
 108  *
 109  * @param rwl
 110  *   A pointer to the rwlock structure.
 111  */
 112 static inline void
 113 rte_rwlock_read_unlock(rte_rwlock_t *rwl)
 114 {
 115         rte_atomic32_dec((rte_atomic32_t *)(intptr_t)&rwl->cnt);
 116 }
 117
 118 /**
 119  * Take a write lock. Loop until the lock is held.
 120  *
 121  * @param rwl
 122  *   A pointer to a rwlock structure.
 123  */
 124 static inline void
 125 rte_rwlock_write_lock(rte_rwlock_t *rwl)
 126 {
 127         int32_t x;
 128         int success = 0;
 129
 130         while (success == 0) {
 131                 x = rwl->cnt;
 132                 /* a lock is held */
 133                 if (x != 0) {
 134                         rte_pause();
 135                         continue;
 136                 }
 137                 success = rte_atomic32_cmpset((volatile uint32_t *)&rwl->cnt,
 138                                               0, -1);
 139         }
 140 }
 141
 142 /**
 143  * Release a write lock.
 144  *
 145  * @param rwl
 146  *   A pointer to a rwlock structure.
 147  */
 148 static inline void
 149 rte_rwlock_write_unlock(rte_rwlock_t *rwl)
 150 {
 151         rte_atomic32_inc((rte_atomic32_t *)(intptr_t)&rwl->cnt);
 152 }
 153
 154 /**
 155  * Try to execute critical section in a hardware memory transaction, if it
 156  * fails or not available take a read lock
 157  *
 158  * NOTE: An attempt to perform a HW I/O operation inside a hardware memory
 159  * transaction always aborts the transaction since the CPU is not able to
 160  * roll-back should the transaction fail. Therefore, hardware transactional
 161  * locks are not advised to be used around rte_eth_rx_burst() and
 162  * rte_eth_tx_burst() calls.
 163  *
 164  * @param rwl
 165  *   A pointer to a rwlock structure.
 166  */
 167 static inline void
 168 rte_rwlock_read_lock_tm(rte_rwlock_t *rwl);
 169
 170 /**
 171  * Commit hardware memory transaction or release the read lock if the lock is used as a fall-back
 172  *
 173  * @param rwl
 174  *   A pointer to the rwlock structure.
 175  */
 176 static inline void
 177 rte_rwlock_read_unlock_tm(rte_rwlock_t *rwl);
 178
 179 /**
 180  * Try to execute critical section in a hardware memory transaction, if it
 181  * fails or not available take a write lock
 182  *
 183  * NOTE: An attempt to perform a HW I/O operation inside a hardware memory
 184  * transaction always aborts the transaction since the CPU is not able to
 185  * roll-back should the transaction fail. Therefore, hardware transactional
 186  * locks are not advised to be used around rte_eth_rx_burst() and
 187  * rte_eth_tx_burst() calls.
 188  *
 189  * @param rwl
 190  *   A pointer to a rwlock structure.
 191  */
 192 static inline void
 193 rte_rwlock_write_lock_tm(rte_rwlock_t *rwl);
 194
 195 /**
 196  * Commit hardware memory transaction or release the write lock if the lock is used as a fall-back
 197  *
 198  * @param rwl
 199  *   A pointer to a rwlock structure.
 200  */
 201 static inline void
 202 rte_rwlock_write_unlock_tm(rte_rwlock_t *rwl);
 203
 204 #ifdef __cplusplus
 205 }
 206 #endif
 207
 208 #endif /* _RTE_RWLOCK_H_ */