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

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.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)
>  	}
>  }
> 
> +/**
Please add the experimental API warning

> + * 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);  }
> 
> +/**
Please add the experimental API warning

> + * 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;
I do not see the other RW lock APIs in this file.

>  	rte_service_lcore_attr_get;
>  	rte_service_lcore_attr_reset_all;
>  	rte_service_may_be_active;
> --
> 2.17.1

Other than the minor comments,
Reviewed-by: Honnappa Nagarahalli <Honnappa.nagarahalli@arm.com>