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authorUlrich Drepper <drepper@redhat.com>2003-01-02 11:01:30 +0000
committerUlrich Drepper <drepper@redhat.com>2003-01-02 11:01:30 +0000
commit05df18c3475157cda8126a07b5bb0f52082a0b67 (patch)
treead9be04821a2ec180444af2c737d104141857206 /nptl/DESIGN-condvar.txt
parentcaf7a872326ee21ad20698baa62ca5599a46d866 (diff)
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Update.
2003-01-02 Ulrich Drepper <drepper@redhat.com> * sysdeps/pthread/bits/pthreadtypes.h (pthread_cond_t): Add padding. * condvar.c: Add symbol versioning. The compatibility versions are the same as the change in the interface does not effect this implementation. * Versions [libpthread]: Add definitions for new pthread_cond_* interfaces for version GLIBC_2.3.2.
Diffstat (limited to 'nptl/DESIGN-condvar.txt')
-rw-r--r--nptl/DESIGN-condvar.txt101
1 files changed, 60 insertions, 41 deletions
diff --git a/nptl/DESIGN-condvar.txt b/nptl/DESIGN-condvar.txt
index 303807be6d..749180ed4b 100644
--- a/nptl/DESIGN-condvar.txt
+++ b/nptl/DESIGN-condvar.txt
@@ -7,49 +7,78 @@ Conditional Variable pseudocode.
struct pthread_cond_t {
- unsigned int lock:
+ unsigned int cond_lock;
internal mutex
- unsigned int nr_wakers:
+ uint64_t total_seq;
- number of threads signalled to be woken up.
+ Total number of threads using the conditional variable.
- unsigned int nr_sleepers:
+ uint64_t wakeup_seq;
- number of threads waiting for the cv.
+ sequence number for next wakeup.
+
+ uint64_t woken_seq;
+
+ sequence number of last woken thread.
}
-#define ALL_THREADS (1 << (BITS_PER_LONG-1))
-cond_wait_timeout(cv, mutex, timeout):
+
+cleanup_handler(cv)
+{
+ lll_lock(cv->lock);
+
+ ++cv->wakeup_seq;
+ ++cv->woken_seq;
+
+ lll_unlock(cv->lock);
+}
+
+
+cond_timedwait(cv, mutex, timeout):
{
lll_lock(cv->lock);
mutex_unlock(mutex);
- cv->nr_sleepers++;
- for (;;) {
+ cleanup_push
+
+ ++cv->total_seq;
+ val = seq = cv->wakeup_seq;
+
+ while (1) {
+
+ lll_unlock(cv->lock);
+
+ enable_async
- if (cv->nr_wakers) {
- cv->nr_wakers--;
- break;
- }
- val = cv->nr_wakers;
+ ret = FUTEX_WAIT(cv->wakeup_seq, val, timeout);
- lll_unlock(cv->lock);
+ restore_async
- ret = FUTEX WAIT (cv->nr_wakers, val, timeout)
+ lll_lock(cv->lock);
- lll_lock(cv->lock);
+ val = cv->wakeup_seq;
- if (ret == TIMEOUT)
- break;
+ if (cv->woken_seq >= seq && cv->woken_seq < val) {
ret = 0;
+ break;
+ }
+
+ if (ret == TIMEDOUT) {
+ ++cv->wakeup_seq;
+ break;
+ }
}
- if (!--cv->nr_sleepers)
- cv->nr_wakers = 0; /* no memory of wakeups */
+
+ ++cv->woken_seq;
+
lll_unlock(cv->lock);
+
+ cleanup_pop
+
mutex_lock(mutex);
return ret;
@@ -57,34 +86,24 @@ cond_wait_timeout(cv, mutex, timeout):
cond_signal(cv)
{
- int do_wakeup = 0;
-
lll_lock(cv->lock);
- if (cv->nr_sleepers) {
- if (!++cv->nr_wakers) /* overflow detection for the nutcase */
- cv->nr_wakers = ALL_THREADS;
- do_wakeup = 1;
+
+ if (cv->total_seq > cv->wakeup_seq) {
+ ++cv->wakeup_seq;
+ FUTEX_WAKE(cv->wakeup_seq, 1);
}
+
lll_unlock(cv->lock);
- if (do_wakeup)
- FUTEX WAKE (cv->nr_wakers, 1)
}
cond_broadcast(cv)
{
- int do_wakeup = 0;
-
lll_lock(cv->lock);
- if (cv->nr_sleepers) {
- cv->nr_wakers |= ALL_THREADS;
- do_wakeup = 1;
+
+ if (cv->total_seq > cv->wakeup_seq) {
+ cv->wakeup_seq = cv->total_seq;
+ FUTEX_WAKE(cv->wakeup_seq, ALL);
}
+
lll_unlock(cv->lock);
- if (do_wakeup)
- FUTEX WAKE (cv->nr_wakers, ALL_THREADS);
}
-
-weaknesses of the implementation:
-
- it might generate spurious wakeups in the broadcast case, but those are
- allowed by POSIX.