[dpdk-dev] [PATCH 1/2] rwlock: introduce 'try' semantics for RD and WR locking

[Konstantin Ananyev <konstantin.ananyev@intel.com>]

This patch targets 19.02 release.

Introduce rte_rwlock_read_trylock() and rte_rwlock_write_trylock().
Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
---
 .../common/include/generic/rte_rwlock.h       | 54 +++++++++++++++++++
 lib/librte_eal/rte_eal_version.map            |  2 +
 2 files changed, 56 insertions(+)

diff --git a/lib/librte_eal/common/include/generic/rte_rwlock.h b/lib/librte_eal/common/include/generic/rte_rwlock.h
index 5751a0e6d..7e395781e 100644
--- a/lib/librte_eal/common/include/generic/rte_rwlock.h
+++ b/lib/librte_eal/common/include/generic/rte_rwlock.h
@@ -75,6 +75,33 @@ rte_rwlock_read_lock(rte_rwlock_t *rwl)
 	}
 }
 
+/**
+ * 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.
  *
@@ -87,6 +114,33 @@ rte_rwlock_read_unlock(rte_rwlock_t *rwl)
 	rte_atomic32_dec((rte_atomic32_t *)(intptr_t)&rwl->cnt);
 }
 
+/**
+ * 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;
+	int success = 0;
+
+	while (success == 0) {
+		x = rwl->cnt;
+		/* a lock is held */
+		if (x != 0)
+			return -EBUSY;
+		success = rte_atomic32_cmpset((volatile uint32_t *)&rwl->cnt,
+					      0, (uint32_t)-1);
+	}
+	return 0;
+}
+
 /**
  * Take a write lock. Loop until the lock is held.
  *
diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
index 3fe78260d..8b1593dd8 100644
--- a/lib/librte_eal/rte_eal_version.map
+++ b/lib/librte_eal/rte_eal_version.map
@@ -355,6 +355,8 @@ EXPERIMENTAL {
 	rte_mp_request_async;
 	rte_mp_sendmsg;
 	rte_option_register;
+	rte_rwlock_read_trylock;
+	rte_rwlock_write_trylock;
 	rte_service_lcore_attr_get;
 	rte_service_lcore_attr_reset_all;
 	rte_service_may_be_active;
-- 
2.17.1