Author: Armin Rigo <[email protected]>
Branch:
Changeset: r201:6b3036be4bb8
Date: 2013-06-20 10:14 +0200
http://bitbucket.org/pypy/stmgc/changeset/6b3036be4bb8/
Log: Revert a part of 9507e1b05a3c: it's not the first time I mess this
up. Add a comment.
diff --git a/c4/demo2.c b/c4/demo2.c
--- a/c4/demo2.c
+++ b/c4/demo2.c
@@ -100,9 +100,10 @@
// results from consecutive read_barriers can differ. needs Ptr_Eq()
int i = 0;
while (!(stm_read_barrier((gcptr)r_prev->next) ==
- stm_read_barrier((gcptr)r_current) &&
+ ((gcptr)r_current) &&
stm_read_barrier((gcptr)r_current->next) ==
- stm_read_barrier((gcptr)r_next))) {
+ ((gcptr)r_next))) {
+ abort();
asm volatile ("pause":::"memory"); /* smp_spinloop() */
i++;
assert(i < 1000);
diff --git a/c4/et.c b/c4/et.c
--- a/c4/et.c
+++ b/c4/et.c
@@ -640,15 +640,34 @@
if (v >= LOCKED) // locked
{
if (!during_commit)
- assert(v != d->my_lock); // we don't hold any lock
-
- if (v != d->my_lock)
{
- /* not locked by me: spinloop until the other thread releases
- its lock */
+ assert(v != d->my_lock); // we don't hold any lock
+ /* spinloop until the other thread releases its lock */
SpinLoop(SPLP_LOCKED_VALIDATE);
goto retry;
}
+ else
+ {
+ if (v != d->my_lock) // not locked by me: conflict
+ {
+ /* A case that can occur: two threads A and B are both
+ committing, thread A locked object a, thread B
+ locked object b, and then thread A tries to
+ validate the reads it did on object b and
+ vice-versa. In this case both threads cannot
+ commit, but if they both enter the SpinLoop()
+ above, then they will livelock.
+
+ XXX This might lead both threads to cancel by
+ reaching this point. It might be possible to be
+ more clever and let one of the threads commit
+ anyway.
+ */
+ fprintf(stderr, "validation failed: "
+ "%p is locked by another thread\n", R);
+ return 0;
+ }
+ }
}
}
return 1;
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