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

[Gavin Hu (Arm Technology China)]

> -----Original Message-----
> From: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
> Sent: Wednesday, December 19, 2018 2:38 PM
> To: Konstantin Ananyev <konstantin.anan...@intel.com>; dev@dpdk.org
> Cc: nd <n...@arm.com>; Honnappa Nagarahalli
> <honnappa.nagaraha...@arm.com>; Gavin Hu (Arm Technology China)
> <gavin...@arm.com>; nd <n...@arm.com>
> Subject: RE: [dpdk-dev] [PATCH 1/2] rwlock: introduce 'try' semantics for RD
> and WR locking
> 
> >
> > This patch targets 19.02 release.
> >
> > Introduce rte_rwlock_read_trylock() and rte_rwlock_write_trylock().
> > Signed-off-by: Konstantin Ananyev <konstantin.anan...@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.nagaraha...@arm.com>
Same comments as Honnappa, experimental warning is required in new code.
Reviewed-by: Gavin Hu <gavin...@arm.com>