aboutsummaryrefslogtreecommitdiff
path: root/nptl
diff options
context:
space:
mode:
authorTorvald Riegel <triegel@redhat.com>2014-12-15 22:49:29 +0100
committerTorvald Riegel <triegel@redhat.com>2014-12-15 22:49:29 +0100
commitd52c62df3d7574906dde1dea23f8a71e85073b06 (patch)
treeb2c4adc4eca4da3caead86e0420b03365897ed1a /nptl
parent045a6bcdd2d9c5c83f01171775998ef3104eb10f (diff)
downloadglibc-d52c62df3d7574906dde1dea23f8a71e85073b06.zip
glibc-d52c62df3d7574906dde1dea23f8a71e85073b06.tar.gz
glibc-d52c62df3d7574906dde1dea23f8a71e85073b06.tar.bz2
Add comments for the generic lowlevellock implementation.
Patch by Bernard Ogden <bernie.ogden@linaro.org>.
Diffstat (limited to 'nptl')
-rw-r--r--nptl/lowlevellock.c21
-rw-r--r--nptl/lowlevelrobustlock.c9
2 files changed, 21 insertions, 9 deletions
diff --git a/nptl/lowlevellock.c b/nptl/lowlevellock.c
index 4c093fc..e1a203b 100644
--- a/nptl/lowlevellock.c
+++ b/nptl/lowlevellock.c
@@ -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;
}
diff --git a/nptl/lowlevelrobustlock.c b/nptl/lowlevelrobustlock.c
index 3525807..291d32a 100644
--- a/nptl/lowlevelrobustlock.c
+++ b/nptl/lowlevelrobustlock.c
@@ -36,14 +36,17 @@ __lll_robust_lock_wait (int *futex, int private)
do
{
+ /* If the owner died, return the present value of the futex. */
if (__glibc_unlikely (oldval & FUTEX_OWNER_DIED))
return oldval;
+ /* Try to put the lock into state 'acquired, possibly with waiters'. */
int newval = oldval | FUTEX_WAITERS;
if (oldval != newval
&& atomic_compare_and_exchange_bool_acq (futex, newval, oldval))
continue;
+ /* If *futex == 2, wait until woken. */
lll_futex_wait (futex, newval, private);
try:
@@ -67,7 +70,7 @@ __lll_robust_timedlock_wait (int *futex, const struct timespec *abstime,
int tid = THREAD_GETMEM (THREAD_SELF, tid);
int oldval = *futex;
- /* If the futex changed meanwhile try locking again. */
+ /* If the futex changed meanwhile, try locking again. */
if (oldval == 0)
goto try;
@@ -100,15 +103,17 @@ __lll_robust_timedlock_wait (int *futex, const struct timespec *abstime,
return ETIMEDOUT;
#endif
- /* Wait. */
+ /* If the owner died, return the present value of the futex. */
if (__glibc_unlikely (oldval & FUTEX_OWNER_DIED))
return oldval;
+ /* Try to put the lock into state 'acquired, possibly with waiters'. */
int newval = oldval | FUTEX_WAITERS;
if (oldval != newval
&& atomic_compare_and_exchange_bool_acq (futex, newval, oldval))
continue;
+ /* If *futex == 2, wait until woken or timeout. */
#if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
|| !defined lll_futex_timed_wait_bitset)
lll_futex_timed_wait (futex, newval, &rt, private);