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MDEV-24271 rw_lock::read_lock_yield() may cause writer starvation

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The greedy fetch_add(1) approach of read_trylock() may cause
starvation of a waiting write lock request. Let us use a
compare-and-swap for the read lock acquisition in order to
guarantee the progress of writers.
This commit is contained in:
Marko Mäkelä 2020-11-24 11:33:39 +02:00
commit 1b12e251cd
2 changed files with 20 additions and 22 deletions
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16
storage/innobase/buf/buf0buf.cc
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@ -281,25 +281,17 @@ the read requests for the whole area.
#ifndef UNIV_INNOCHECKSUM
void page_hash_latch::read_lock_wait()
{
auto l= read_lock_yield();
/* First, try busy spinning for a while. */
for (auto spin= srv_n_spin_wait_rounds; spin--; )
{
if (l & WRITER_PENDING)
ut_delay(srv_spin_wait_delay);
ut_delay(srv_spin_wait_delay);
if (read_trylock())
return;
l= read_lock_yield();
}
/* Fall back to yielding to other threads. */
for (;;)
{
if (l & WRITER_PENDING)
os_thread_yield();
if (read_trylock())
return;
l= read_lock_yield();
}
do
os_thread_yield();
while (!read_trylock());
}
void page_hash_latch::write_lock_wait()