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Re: [PATCH v4 04/12] nptl: Add clockid parameter to futex timed wait calls
On 18/06/2019 13:33, Mike Crowe wrote:
> In preparation for adding POSIX clockwait variants of timedwait functions,
> add a clockid_t parameter to futex_abstimed_wait functions and pass
> CLOCK_REALTIME from all callers for the time being.
>
> Replace lll_futex_timed_wait_bitset with lll_futex_clock_wait_bitset which
> takes a clockid_t parameter rather than the magic clockbit.
>
> * sysdeps/nptl/lowlevellock-futex.h,
> sysdeps/unix/sysv/linux/lowlevellock-futex.h: Replace
> lll_futex_timed_wait_bitset with lll_futex_clock_wait_bitset that takes a
> clockid rather than a special clockbit.
>
> * sysdeps/nptl/lowlevellock-futex.h: Add lll_futex_supported_clockid so
> that client functions can check whether their clockid parameter is valid
> even if they don't ultimately end up calling lll_futex_clock_wait_bitset.
>
> * sysdeps/nptl/futex-internal.h, sysdeps/unix/sysv/linux/futex-internal.h
> (futex_abstimed_wait, futex_abstimed_wait_cancelable): Add clockid_t
> parameter to indicate which clock the absolute time passed should be
> measured against. Pass that clockid onto lll_futex_clock_wait_bitset.
> Add invalid clock as reason for returning -EINVAL.
>
> * sysdeps/nptl/futex-internal.h, sysdeps/unix/sysv/linux/futex-internal.h:
> Introduce futex_abstimed_supported_clockid so that client functions can
> check whether their clockid parameter is valid even if they don't
> ultimately end up calling futex_abstimed_wait.
>
> * nptl/pthread_cond_wait.c (__pthread_cond_wait_common): Remove code to
> calculate relative timeout for __PTHREAD_COND_CLOCK_MONOTONIC_MASK and
> just pass CLOCK_MONOTONIC or CLOCK_REALTIME as required to
> futex_abstimed_wait_cancelable.
>
> * nptl/pthread_rwlock_common (__pthread_rwlock_rdlock_full,
> __pthread_wrlock_full), nptl/sem_waitcommon (do_futex_wait): Pass
> additional CLOCK_REALTIME to futex_abstimed_wait_cancelable.
>
> * nptl/pthread_mutex_timedlock.c (__pthread_mutex_timedlock): Switch to
> lll_futex_clock_wait_bitset and pass CLOCK_REALTIME
LGTM, I will commit this for you.
> ---
> ChangeLog | 40 +++++++++++++++++++++-
> nptl/pthread_cond_wait.c | 32 +++--------------
> nptl/pthread_mutex_timedlock.c | 4 +-
> nptl/pthread_rwlock_common.c | 8 ++--
> nptl/sem_waitcommon.c | 6 ++-
> sysdeps/nptl/futex-internal.h | 9 ++++-
> sysdeps/nptl/lowlevellock-futex.h | 13 ++++---
> sysdeps/unix/sysv/linux/futex-internal.h | 26 ++++++++++----
> sysdeps/unix/sysv/linux/lowlevellock-futex.h | 33 +++++++++++++----
> 9 files changed, 119 insertions(+), 52 deletions(-)
>
> diff --git a/ChangeLog b/ChangeLog
> index e6b36b5..dc84553 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -1,3 +1,43 @@
> +2019-05-27 Mike Crowe <mac@mcrowe.com>
> +
> + nptl: Add clockid parameter to futex timed wait calls
> +
> + * sysdeps/nptl/lowlevellock-futex.h,
> + sysdeps/unix/sysv/linux/lowlevellock-futex.h: Replace
> + lll_futex_timed_wait_bitset with lll_futex_clock_wait_bitset that
> + takes a clockid rather than a special clockbit.
> +
> + * sysdeps/nptl/lowlevellock-futex.h: Add
> + lll_futex_supported_clockid so that client functions can check
> + whether their clockid parameter is valid even if they don't
> + ultimately end up calling lll_futex_clock_wait_bitset.
> +
> + * sysdeps/nptl/futex-internal.h,
> + sysdeps/unix/sysv/linux/futex-internal.h
> + (futex_abstimed_wait, futex_abstimed_wait_cancelable): Add
> + clockid_t parameter to indicate which clock the absolute time
> + passed should be measured against. Pass that clockid onto
> + lll_futex_clock_wait_bitset. Add invalid clock as reason for
> + returning -EINVAL.
> +
> + * sysdeps/nptl/futex-internal.h,
> + sysdeps/unix/sysv/linux/futex-internal.h: Introduce
> + futex_abstimed_supported_clockid so that client functions can check
> + whether their clockid parameter is valid even if they don't
> + ultimately end up calling futex_abstimed_wait.
> +
> + * nptl/pthread_cond_wait.c (__pthread_cond_wait_common): Remove
> + code to calculate relative timeout for
> + __PTHREAD_COND_CLOCK_MONOTONIC_MASK and just pass CLOCK_MONOTONIC
> + or CLOCK_REALTIME as required to futex_abstimed_wait_cancelable.
> +
> + * nptl/pthread_rwlock_common (__pthread_rwlock_rdlock_full)
> + (__pthread_wrlock_full), nptl/sem_waitcommon (do_futex_wait): Pass
> + additional CLOCK_REALTIME to futex_abstimed_wait_cancelable.
> +
> + * nptl/pthread_mutex_timedlock.c (__pthread_mutex_timedlock):
> + Switch to lll_futex_clock_wait_bitset and pass CLOCK_REALTIME
> +
> 2019-05-30 Mike Crowe <mac@mcrowe.com>
>
> * nptl/eintr.c: Use libsupport.
> diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
> index 9a0f29e..7385562 100644
> --- a/nptl/pthread_cond_wait.c
> +++ b/nptl/pthread_cond_wait.c
> @@ -509,35 +509,15 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
> values despite them being valid. */
> if (__glibc_unlikely (abstime->tv_sec < 0))
> err = ETIMEDOUT;
> -
> - else if ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0)
> - {
> - /* CLOCK_MONOTONIC is requested. */
> - struct timespec rt;
> - if (__clock_gettime (CLOCK_MONOTONIC, &rt) != 0)
> - __libc_fatal ("clock_gettime does not support "
> - "CLOCK_MONOTONIC\n");
> - /* Convert the absolute timeout value to a relative
> - timeout. */
> - rt.tv_sec = abstime->tv_sec - rt.tv_sec;
> - rt.tv_nsec = abstime->tv_nsec - rt.tv_nsec;
> - if (rt.tv_nsec < 0)
> - {
> - rt.tv_nsec += 1000000000;
> - --rt.tv_sec;
> - }
> - /* Did we already time out? */
> - if (__glibc_unlikely (rt.tv_sec < 0))
> - err = ETIMEDOUT;
> - else
> - err = futex_reltimed_wait_cancelable
> - (cond->__data.__g_signals + g, 0, &rt, private);
> - }
> else
> {
> - /* Use CLOCK_REALTIME. */
> + const clockid_t clockid =
> + ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0) ?
> + CLOCK_MONOTONIC : CLOCK_REALTIME;
> +
> err = futex_abstimed_wait_cancelable
> - (cond->__data.__g_signals + g, 0, abstime, private);
> + (cond->__data.__g_signals + g, 0, clockid, abstime,
> + private);
> }
> }
>
> diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
> index 270b072..d4d11cc 100644
> --- a/nptl/pthread_mutex_timedlock.c
> +++ b/nptl/pthread_mutex_timedlock.c
> @@ -266,8 +266,8 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex,
> assume_other_futex_waiters |= FUTEX_WAITERS;
>
> /* Block using the futex. */
> - int err = lll_futex_timed_wait_bitset (&mutex->__data.__lock,
> - oldval, abstime, FUTEX_CLOCK_REALTIME,
> + int err = lll_futex_clock_wait_bitset (&mutex->__data.__lock,
> + oldval, CLOCK_REALTIME, abstime,
> PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
> /* The futex call timed out. */
> if (err == -ETIMEDOUT)
> diff --git a/nptl/pthread_rwlock_common.c b/nptl/pthread_rwlock_common.c
> index 2560734..89ba21a 100644
> --- a/nptl/pthread_rwlock_common.c
> +++ b/nptl/pthread_rwlock_common.c
> @@ -319,7 +319,7 @@ __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
> {
> int private = __pthread_rwlock_get_private (rwlock);
> int err = futex_abstimed_wait (&rwlock->__data.__readers,
> - r, abstime, private);
> + r, CLOCK_REALTIME, abstime, private);
> /* We ignore EAGAIN and EINTR. On time-outs, we can just
> return because we don't need to clean up anything. */
> if (err == ETIMEDOUT)
> @@ -447,7 +447,7 @@ __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
> continue;
> int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
> 1 | PTHREAD_RWLOCK_FUTEX_USED,
> - abstime, private);
> + CLOCK_REALTIME, abstime, private);
> if (err == ETIMEDOUT)
> {
> /* If we timed out, we need to unregister. If no read phase
> @@ -707,7 +707,7 @@ __pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
> may_share_futex_used_flag = true;
> int err = futex_abstimed_wait (&rwlock->__data.__writers_futex,
> 1 | PTHREAD_RWLOCK_FUTEX_USED,
> - abstime, private);
> + CLOCK_REALTIME, abstime, private);
> if (err == ETIMEDOUT)
> {
> if (prefer_writer)
> @@ -806,7 +806,7 @@ __pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
> continue;
> int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
> PTHREAD_RWLOCK_FUTEX_USED,
> - abstime, private);
> + CLOCK_REALTIME, abstime, private);
> if (err == ETIMEDOUT)
> {
> if (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP)
> diff --git a/nptl/sem_waitcommon.c b/nptl/sem_waitcommon.c
> index 5646bea..425d040 100644
> --- a/nptl/sem_waitcommon.c
> +++ b/nptl/sem_waitcommon.c
> @@ -109,11 +109,13 @@ do_futex_wait (struct new_sem *sem, const struct timespec *abstime)
>
> #if __HAVE_64B_ATOMICS
> err = futex_abstimed_wait_cancelable (
> - (unsigned int *) &sem->data + SEM_VALUE_OFFSET, 0, abstime,
> + (unsigned int *) &sem->data + SEM_VALUE_OFFSET, 0,
> + CLOCK_REALTIME, abstime,
> sem->private);
> #else
> err = futex_abstimed_wait_cancelable (&sem->value, SEM_NWAITERS_MASK,
> - abstime, sem->private);
> + CLOCK_REALTIME, abstime,
> + sem->private);
> #endif
>
> return err;
> diff --git a/sysdeps/nptl/futex-internal.h b/sysdeps/nptl/futex-internal.h
> index 86a0818..bc29bdb 100644
> --- a/sysdeps/nptl/futex-internal.h
> +++ b/sysdeps/nptl/futex-internal.h
> @@ -49,7 +49,7 @@
> futex word.
>
> Both absolute and relative timeouts can be used. An absolute timeout
> - expires when the given specific point in time on the CLOCK_REALTIME clock
> + expires when the given specific point in time on the specified clock
> passes, or when it already has passed. A relative timeout expires when
> the given duration of time on the CLOCK_MONOTONIC clock passes. Relative
> timeouts may be imprecise (see futex_supports_exact_relative_timeouts).
> @@ -159,16 +159,23 @@ futex_reltimed_wait_cancelable (unsigned int* futex_word,
> unsigned int expected,
> const struct timespec* reltime, int private);
>
> +/* Check whether the specified clockid is supported by
> + futex_abstimed_wait and futex_abstimed_wait_cancelable. */
> +static __always_inline int
> +futex_abstimed_supported_clockid (clockid_t clockid);
> +
> /* Like futex_reltimed_wait, but the provided timeout (ABSTIME) is an
> absolute point in time; a call will time out after this point in time. */
> static __always_inline int
> futex_abstimed_wait (unsigned int* futex_word, unsigned int expected,
> + clockid_t clockid,
> const struct timespec* abstime, int private);
>
> /* Like futex_reltimed_wait but is a POSIX cancellation point. */
> static __always_inline int
> futex_abstimed_wait_cancelable (unsigned int* futex_word,
> unsigned int expected,
> + clockid_t clockid,
> const struct timespec* abstime, int private);
>
> /* Atomically wrt other futex operations on the same futex, this unblocks the
> diff --git a/sysdeps/nptl/lowlevellock-futex.h b/sysdeps/nptl/lowlevellock-futex.h
> index 63d917d..35fcfbb 100644
> --- a/sysdeps/nptl/lowlevellock-futex.h
> +++ b/sysdeps/nptl/lowlevellock-futex.h
> @@ -43,10 +43,15 @@
> #define lll_futex_timed_wait(futexp, val, timeout, private) \
> -ENOSYS
>
> -/* If CLOCKBIT is zero, this is identical to lll_futex_timed_wait.
> - If CLOCKBIT has FUTEX_CLOCK_REALTIME set, then it's the same but
> - TIMEOUT is counted by CLOCK_REALTIME rather than CLOCK_MONOTONIC. */
> -#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
> +/* Verify whether the supplied clockid is supported by
> + lll_futex_clock_wait_bitset */
> +#define lll_futex_supported_clockid(clockid) \
> + (0)
> +
> +/* Wait until a lll_futex_wake call on FUTEXP, or the absolute TIMEOUT
> + measured against CLOCKID elapses. CLOCKID may be CLOCK_REALTIME or
> + CLOCK_MONOTONIC. */
> +#define lll_futex_clock_wait_bitset(futexp, val, clockid, timeout, private) \
> -ENOSYS
>
> /* Wake up up to NR waiters on FUTEXP. */
> diff --git a/sysdeps/unix/sysv/linux/futex-internal.h b/sysdeps/unix/sysv/linux/futex-internal.h
> index 501f993..03312d6 100644
> --- a/sysdeps/unix/sysv/linux/futex-internal.h
> +++ b/sysdeps/unix/sysv/linux/futex-internal.h
> @@ -162,15 +162,24 @@ futex_reltimed_wait_cancelable (unsigned int *futex_word,
>
> /* See sysdeps/nptl/futex-internal.h for details. */
> static __always_inline int
> +futex_abstimed_supported_clockid (clockid_t clockid)
> +{
> + return lll_futex_supported_clockid (clockid);
> +}
> +
> +/* See sysdeps/nptl/futex-internal.h for details. */
> +static __always_inline int
> futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
> + clockid_t clockid,
> const struct timespec *abstime, int private)
> {
> /* Work around the fact that the kernel rejects negative timeout values
> despite them being valid. */
> if (__glibc_unlikely ((abstime != NULL) && (abstime->tv_sec < 0)))
> return ETIMEDOUT;
> - int err = lll_futex_timed_wait_bitset (futex_word, expected, abstime,
> - FUTEX_CLOCK_REALTIME, private);
> + int err = lll_futex_clock_wait_bitset (futex_word, expected,
> + clockid, abstime,
> + private);
> switch (err)
> {
> case 0:
> @@ -180,9 +189,10 @@ futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
> return -err;
>
> case -EFAULT: /* Must have been caused by a glibc or application bug. */
> - case -EINVAL: /* Either due to wrong alignment or due to the timeout not
> - being normalized. Must have been caused by a glibc or
> - application bug. */
> + case -EINVAL: /* Either due to wrong alignment, unsupported
> + clockid or due to the timeout not being
> + normalized. Must have been caused by a glibc or
> + application bug. */
> case -ENOSYS: /* Must have been caused by a glibc bug. */
> /* No other errors are documented at this time. */
> default:
> @@ -194,6 +204,7 @@ futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
> static __always_inline int
> futex_abstimed_wait_cancelable (unsigned int *futex_word,
> unsigned int expected,
> + clockid_t clockid,
> const struct timespec *abstime, int private)
> {
> /* Work around the fact that the kernel rejects negative timeout values
> @@ -202,8 +213,9 @@ futex_abstimed_wait_cancelable (unsigned int *futex_word,
> return ETIMEDOUT;
> int oldtype;
> oldtype = __pthread_enable_asynccancel ();
> - int err = lll_futex_timed_wait_bitset (futex_word, expected, abstime,
> - FUTEX_CLOCK_REALTIME, private);
> + int err = lll_futex_clock_wait_bitset (futex_word, expected,
> + clockid, abstime,
> + private);
> __pthread_disable_asynccancel (oldtype);
> switch (err)
> {
> diff --git a/sysdeps/unix/sysv/linux/lowlevellock-futex.h b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
> index 030a14b..ba01197 100644
> --- a/sysdeps/unix/sysv/linux/lowlevellock-futex.h
> +++ b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
> @@ -82,12 +82,33 @@
> __lll_private_flag (FUTEX_WAIT, private), \
> val, timeout)
>
> -#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
> - lll_futex_syscall (6, futexp, \
> - __lll_private_flag (FUTEX_WAIT_BITSET | (clockbit), \
> - private), \
> - val, timeout, NULL /* Unused. */, \
> - FUTEX_BITSET_MATCH_ANY)
> +/* Verify whether the supplied clockid is supported by
> + lll_futex_clock_wait_bitset */
> +#define lll_futex_supported_clockid(clockid) \
> + ((clockid) == CLOCK_REALTIME || (clockid) == CLOCK_MONOTONIC)
> +
> +/* The kernel currently only supports CLOCK_MONOTONIC or
> + * CLOCK_REALTIME timeouts for FUTEX_WAIT_BITSET. We could attempt to
> + * convert others here but currently do not.
> + */
> +#define lll_futex_clock_wait_bitset(futexp, val, clockid, timeout, private) \
> + ({ \
> + long int __ret; \
> + if (lll_futex_supported_clockid (clockid)) \
> + { \
> + const unsigned int clockbit = \
> + (clockid == CLOCK_REALTIME) ? FUTEX_CLOCK_REALTIME : 0; \
> + const int op = \
> + __lll_private_flag (FUTEX_WAIT_BITSET | clockbit, private); \
> + \
> + __ret = lll_futex_syscall (6, futexp, op, val, \
> + timeout, NULL /* Unused. */, \
> + FUTEX_BITSET_MATCH_ANY); \
> + } \
> + else \
> + __ret = -EINVAL; \
> + __ret; \
> + })
>
> #define lll_futex_wake(futexp, nr, private) \
> lll_futex_syscall (4, futexp, \
>