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Add comments for the generic lowlevellock implementation.

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Patch by Bernard Ogden <bernie.ogden@linaro.org>.
This commit is contained in:
Torvald Riegel
2014-12-15 22:49:29 +01:00
parent 045a6bcdd2
commit d52c62df3d
4 changed files with 124 additions and 18 deletions
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21
nptl/lowlevellock.c
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@@ -27,10 +27,10 @@ void
__lll_lock_wait_private (int *futex)
{
if (*futex == 2)
lll_futex_wait (futex, 2, LLL_PRIVATE);
lll_futex_wait (futex, 2, LLL_PRIVATE); /* Wait if *futex == 2. */
while (atomic_exchange_acq (futex, 2) != 0)
lll_futex_wait (futex, 2, LLL_PRIVATE);
lll_futex_wait (futex, 2, LLL_PRIVATE); /* Wait if *futex == 2. */
}
@@ -40,10 +40,10 @@ void
__lll_lock_wait (int *futex, int private)
{
if (*futex == 2)
lll_futex_wait (futex, 2, private);
lll_futex_wait (futex, 2, private); /* Wait if *futex == 2. */
while (atomic_exchange_acq (futex, 2) != 0)
lll_futex_wait (futex, 2, private);
lll_futex_wait (futex, 2, private); /* Wait if *futex == 2. */
}
@@ -75,7 +75,7 @@ __lll_timedlock_wait (int *futex, const struct timespec *abstime, int private)
if (rt.tv_sec < 0)
return ETIMEDOUT;
/* Wait. */
/* If *futex == 2, wait until woken or timeout. */
lll_futex_timed_wait (futex, 2, &rt, private);
}
@@ -83,6 +83,11 @@ __lll_timedlock_wait (int *futex, const struct timespec *abstime, int private)
}
/* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via futex
wake-up when the clone terminates. The memory location contains the
thread ID while the clone is running and is reset to zero by the kernel
afterwards. The kernel up to version 3.16.3 does not use the private futex
operations for futex wake-up when the clone terminates. */
int
__lll_timedwait_tid (int *tidp, const struct timespec *abstime)
{
@@ -113,8 +118,10 @@ __lll_timedwait_tid (int *tidp, const struct timespec *abstime)
if (rt.tv_sec < 0)
return ETIMEDOUT;
/* Wait until thread terminates. The kernel so far does not use
the private futex operations for this. */
/* If *tidp == tid, wait until thread terminates or the wait times out.
The kernel up to version 3.16.3 does not use the private futex
operations for futex wake-up when the clone terminates.
*/
if (lll_futex_timed_wait (tidp, tid, &rt, LLL_SHARED) == -ETIMEDOUT)
return ETIMEDOUT;
}