rwlock: introduce try semantics

[dpdk.git] / lib / librte_eal / common / include / generic / rte_rwlock.h

diff --git a/lib/librte_eal/common/include/generic/rte_rwlock.h b/lib/librte_eal/common/include/generic/rte_rwlock.h
index fdb3113..b05d85a 100644 (file)
--- a/lib/librte_eal/common/include/generic/rte_rwlock.h
+++ b/lib/librte_eal/common/include/generic/rte_rwlock.h
@@ -1,34 +1,5 @@
-/*-
- *   BSD LICENSE
- *
- *   Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
- *   All rights reserved.
- *
- *   Redistribution and use in source and binary forms, with or without
- *   modification, are permitted provided that the following conditions
- *   are met:
- *
- *     * Redistributions of source code must retain the above copyright
- *       notice, this list of conditions and the following disclaimer.
- *     * Redistributions in binary form must reproduce the above copyright
- *       notice, this list of conditions and the following disclaimer in
- *       the documentation and/or other materials provided with the
- *       distribution.
- *     * Neither the name of Intel Corporation nor the names of its
- *       contributors may be used to endorse or promote products derived
- *       from this software without specific prior written permission.
- *
- *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2010-2014 Intel Corporation
  */
 
 #ifndef _RTE_RWLOCK_H_
@@ -100,10 +71,40 @@ rte_rwlock_read_lock(rte_rwlock_t *rwl)
                        continue;
                }
                success = rte_atomic32_cmpset((volatile uint32_t *)&rwl->cnt,
-                                             x, x + 1);
+                                             (uint32_t)x, (uint32_t)(x + 1));
        }
 }
 
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * try to take a read lock.
+ *
+ * @param rwl
+ *   A pointer to a rwlock structure.
+ * @return
+ *   - zero if the lock is successfully taken
+ *   - -EBUSY if lock could not be acquired for reading because a
+ *     writer holds the lock
+ */
+static inline __rte_experimental int
+rte_rwlock_read_trylock(rte_rwlock_t *rwl)
+{
+       int32_t x;
+       int success = 0;
+
+       while (success == 0) {
+               x = rwl->cnt;
+               /* write lock is held */
+               if (x < 0)
+                       return -EBUSY;
+               success = rte_atomic32_cmpset((volatile uint32_t *)&rwl->cnt,
+                                             (uint32_t)x, (uint32_t)(x + 1));
+       }
+       return 0;
+}
+
 /**
  * Release a read lock.
  *
@@ -116,6 +117,32 @@ rte_rwlock_read_unlock(rte_rwlock_t *rwl)
        rte_atomic32_dec((rte_atomic32_t *)(intptr_t)&rwl->cnt);
 }
 
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * try to take a write lock.
+ *
+ * @param rwl
+ *   A pointer to a rwlock structure.
+ * @return
+ *   - zero if the lock is successfully taken
+ *   - -EBUSY if lock could not be acquired for writing because
+ *     it was already locked for reading or writing
+ */
+static inline __rte_experimental int
+rte_rwlock_write_trylock(rte_rwlock_t *rwl)
+{
+       int32_t x;
+
+       x = rwl->cnt;
+       if (x != 0 || rte_atomic32_cmpset((volatile uint32_t *)&rwl->cnt,
+                               0, (uint32_t)-1) == 0)
+               return -EBUSY;
+
+       return 0;
+}
+
 /**
  * Take a write lock. Loop until the lock is held.
  *
@@ -136,7 +163,7 @@ rte_rwlock_write_lock(rte_rwlock_t *rwl)
                        continue;
                }
                success = rte_atomic32_cmpset((volatile uint32_t *)&rwl->cnt,
-                                             0, -1);
+                                             0, (uint32_t)-1);
        }
 }