qiurui
/
glibc
mirror of git://sourceware.org/git/glibc.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

nptl: Update comments and indentation for new condvar implementation 

Some comments were wrong after the most recent commit. This fixes that.

Also fixing indentation where it was using spaces instead of tabs.

Signed-off-by: Malte Skarupke <malteskarupke@fastmail.fm>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Malte Skarupke 2024-12-04 07:55:22 -05:00 committed by Carlos O'Donell
parent 1db84775f8
commit 0cc973160c
2 changed files with 22 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
nptl/pthread_cond_common.c
View File

@ -221,8 +221,9 @@ __condvar_quiesce_and_switch_g1 (pthread_cond_t *cond, uint64_t wseq,
* New waiters arriving concurrently with the group switching will all go
into G2 until we atomically make the switch. Waiters existing in G2
are not affected.
* Waiters in G1 will be closed out immediately by the advancing of
__g_signals to the next "lowseq" (low 31 bits of the new g1_start),
* Waiters in G1 have already received a signal and been woken. If they
haven't woken yet, they will be closed out immediately by the advancing
of __g_signals to the next "lowseq" (low 31 bits of the new g1_start),
which will prevent waiters from blocking using a futex on
__g_signals since it provides enough signals for all possible
remaining waiters. As a result, they can each consume a signal

39
nptl/pthread_cond_wait.c
View File

@ -249,7 +249,7 @@ __condvar_cleanup_waiting (void *arg)
figure out whether they are in a group that has already been completely
signaled (i.e., if the current G1 starts at a later position that the
waiter's position). Waiters cannot determine whether they are currently
in G2 or G1 -- but they do not have too because all they are interested in
in G2 or G1 -- but they do not have to because all they are interested in
is whether there are available signals, and they always start in G2 (whose
group slot they know because of the bit in the waiter sequence. Signalers
will simply fill the right group until it is completely signaled and can
@ -412,7 +412,7 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
}
/* Now wait until a signal is available in our group or it is closed.
Acquire MO so that if we observe a value of zero written after group
Acquire MO so that if we observe (signals == lowseq) after group
switching in __condvar_quiesce_and_switch_g1, we synchronize with that
store and will see the prior update of __g1_start done while switching
groups too. */
@ -422,8 +422,8 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
{
while (1)
{
uint64_t g1_start = __condvar_load_g1_start_relaxed (cond);
unsigned int lowseq = (g1_start & 1) == g ? signals : g1_start & ~1U;
uint64_t g1_start = __condvar_load_g1_start_relaxed (cond);
unsigned int lowseq = (g1_start & 1) == g ? signals : g1_start & ~1U;
/* Spin-wait first.
Note that spinning first without checking whether a timeout
@ -447,21 +447,21 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
/* Reload signals. See above for MO. */
signals = atomic_load_acquire (cond->__data.__g_signals + g);
g1_start = __condvar_load_g1_start_relaxed (cond);
lowseq = (g1_start & 1) == g ? signals : g1_start & ~1U;
g1_start = __condvar_load_g1_start_relaxed (cond);
lowseq = (g1_start & 1) == g ? signals : g1_start & ~1U;
spin--;
}
if (seq < (g1_start >> 1))
if (seq < (g1_start >> 1))
{
/* If the group is closed already,
/* If the group is closed already,
then this waiter originally had enough extra signals to
consume, up until the time its group was closed. */
goto done;
}
}
/* If there is an available signal, don't block.
If __g1_start has advanced at all, then we must be in G1
If __g1_start has advanced at all, then we must be in G1
by now, perhaps in the process of switching back to an older
G2, but in either case we're allowed to consume the available
signal and should not block anymore. */
@ -483,22 +483,23 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
sequence. */
atomic_fetch_add_acquire (cond->__data.__g_refs + g, 2);
signals = atomic_load_acquire (cond->__data.__g_signals + g);
g1_start = __condvar_load_g1_start_relaxed (cond);
lowseq = (g1_start & 1) == g ? signals : g1_start & ~1U;
g1_start = __condvar_load_g1_start_relaxed (cond);
lowseq = (g1_start & 1) == g ? signals : g1_start & ~1U;
if (seq < (g1_start >> 1))
if (seq < (g1_start >> 1))
{
/* group is closed already, so don't block */
/* group is closed already, so don't block */
__condvar_dec_grefs (cond, g, private);
goto done;
}
if ((int)(signals - lowseq) >= 2)
{
/* a signal showed up or G1/G2 switched after we grabbed the refcount */
/* a signal showed up or G1/G2 switched after we grabbed the
refcount */
__condvar_dec_grefs (cond, g, private);
break;
}
}
// Now block.
struct _pthread_cleanup_buffer buffer;
@ -536,10 +537,8 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
if (seq < (__condvar_load_g1_start_relaxed (cond) >> 1))
goto done;
}
/* Try to grab a signal. Use acquire MO so that we see an up-to-date value
of __g1_start below (see spinning above for a similar case). In
particular, if we steal from a more recent group, we will also see a
more recent __g1_start below. */
/* Try to grab a signal. See above for MO. (if we do another loop
iteration we need to see the correct value of g1_start) */
while (!atomic_compare_exchange_weak_acquire (cond->__data.__g_signals + g,
&signals, signals - 2));