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Once again allow LWLocks to be used within DSM segments.

Browse Source 
Prior to commit 7882c3b0b9, it was
possible to use LWLocks within DSM segments, but that commit broke
this use case by switching from a doubly linked list to a circular
linked list.  Switch back, using a new bit of general infrastructure
for maintaining lists of PGPROCs.

Thomas Munro, reviewed by me.
This commit is contained in:
Robert Haas
2016-08-15 18:09:55 -04:00
parent 2bf06f7561
commit b25b6c9701
6 changed files with 240 additions and 35 deletions
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63
src/backend/storage/lmgr/lwlock.c
View File

@@ -84,6 +84,7 @@
#include "storage/ipc.h"
#include "storage/predicate.h"
#include "storage/proc.h"
#include "storage/proclist.h"
#include "storage/spin.h"
#include "utils/memutils.h"
@@ -717,7 +718,7 @@ LWLockInitialize(LWLock *lock, int tranche_id)
pg_atomic_init_u32(&lock->nwaiters, 0);
#endif
lock->tranche = tranche_id;
dlist_init(&lock->waiters);
proclist_init(&lock->waiters);
}
/*
@@ -920,25 +921,25 @@ LWLockWakeup(LWLock *lock)
{
bool new_release_ok;
bool wokeup_somebody = false;
dlist_head wakeup;
dlist_mutable_iter iter;
proclist_head wakeup;
proclist_mutable_iter iter;
dlist_init(&wakeup);
proclist_init(&wakeup);
new_release_ok = true;
/* lock wait list while collecting backends to wake up */
LWLockWaitListLock(lock);
dlist_foreach_modify(iter, &lock->waiters)
proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
{
PGPROC *waiter = dlist_container(PGPROC, lwWaitLink, iter.cur);
PGPROC *waiter = GetPGProcByNumber(iter.cur);
if (wokeup_somebody && waiter->lwWaitMode == LW_EXCLUSIVE)
continue;
dlist_delete(&waiter->lwWaitLink);
dlist_push_tail(&wakeup, &waiter->lwWaitLink);
proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
proclist_push_tail(&wakeup, iter.cur, lwWaitLink);
if (waiter->lwWaitMode != LW_WAIT_UNTIL_FREE)
{
@@ -963,7 +964,7 @@ LWLockWakeup(LWLock *lock)
break;
}
Assert(dlist_is_empty(&wakeup) || pg_atomic_read_u32(&lock->state) & LW_FLAG_HAS_WAITERS);
Assert(proclist_is_empty(&wakeup) || pg_atomic_read_u32(&lock->state) & LW_FLAG_HAS_WAITERS);
/* unset required flags, and release lock, in one fell swoop */
{
@@ -982,7 +983,7 @@ LWLockWakeup(LWLock *lock)
else
desired_state &= ~LW_FLAG_RELEASE_OK;
if (dlist_is_empty(&wakeup))
if (proclist_is_empty(&wakeup))
desired_state &= ~LW_FLAG_HAS_WAITERS;
desired_state &= ~LW_FLAG_LOCKED; /* release lock */
@@ -994,12 +995,12 @@ LWLockWakeup(LWLock *lock)
}
/* Awaken any waiters I removed from the queue. */
dlist_foreach_modify(iter, &wakeup)
proclist_foreach_modify(iter, &wakeup, lwWaitLink)
{
PGPROC *waiter = dlist_container(PGPROC, lwWaitLink, iter.cur);
PGPROC *waiter = GetPGProcByNumber(iter.cur);
LOG_LWDEBUG("LWLockRelease", lock, "release waiter");
dlist_delete(&waiter->lwWaitLink);
proclist_delete(&wakeup, iter.cur, lwWaitLink);
/*
* Guarantee that lwWaiting being unset only becomes visible once the
@@ -1046,9 +1047,9 @@ LWLockQueueSelf(LWLock *lock, LWLockMode mode)
/* LW_WAIT_UNTIL_FREE waiters are always at the front of the queue */
if (mode == LW_WAIT_UNTIL_FREE)
dlist_push_head(&lock->waiters, &MyProc->lwWaitLink);
proclist_push_head(&lock->waiters, MyProc->pgprocno, lwWaitLink);
else
dlist_push_tail(&lock->waiters, &MyProc->lwWaitLink);
proclist_push_tail(&lock->waiters, MyProc->pgprocno, lwWaitLink);
/* Can release the mutex now */
LWLockWaitListUnlock(lock);
@@ -1070,7 +1071,7 @@ static void
LWLockDequeueSelf(LWLock *lock)
{
bool found = false;
dlist_mutable_iter iter;
proclist_mutable_iter iter;
#ifdef LWLOCK_STATS
lwlock_stats *lwstats;
@@ -1086,19 +1087,17 @@ LWLockDequeueSelf(LWLock *lock)
* Can't just remove ourselves from the list, but we need to iterate over
* all entries as somebody else could have unqueued us.
*/
dlist_foreach_modify(iter, &lock->waiters)
proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
{
PGPROC *proc = dlist_container(PGPROC, lwWaitLink, iter.cur);
if (proc == MyProc)
if (iter.cur == MyProc->pgprocno)
{
found = true;
dlist_delete(&proc->lwWaitLink);
proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
break;
}
}
if (dlist_is_empty(&lock->waiters) &&
if (proclist_is_empty(&lock->waiters) &&
(pg_atomic_read_u32(&lock->state) & LW_FLAG_HAS_WAITERS) != 0)
{
pg_atomic_fetch_and_u32(&lock->state, ~LW_FLAG_HAS_WAITERS);
@@ -1719,12 +1718,12 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
void
LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
{
dlist_head wakeup;
dlist_mutable_iter iter;
proclist_head wakeup;
proclist_mutable_iter iter;
PRINT_LWDEBUG("LWLockUpdateVar", lock, LW_EXCLUSIVE);
dlist_init(&wakeup);
proclist_init(&wakeup);
LWLockWaitListLock(lock);
@@ -1737,15 +1736,15 @@ LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
* See if there are any LW_WAIT_UNTIL_FREE waiters that need to be woken
* up. They are always in the front of the queue.
*/
dlist_foreach_modify(iter, &lock->waiters)
proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
{
PGPROC *waiter = dlist_container(PGPROC, lwWaitLink, iter.cur);
PGPROC *waiter = GetPGProcByNumber(iter.cur);
if (waiter->lwWaitMode != LW_WAIT_UNTIL_FREE)
break;
dlist_delete(&waiter->lwWaitLink);
dlist_push_tail(&wakeup, &waiter->lwWaitLink);
proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
proclist_push_tail(&wakeup, iter.cur, lwWaitLink);
}
/* We are done updating shared state of the lock itself. */
@@ -1754,11 +1753,11 @@ LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
/*
* Awaken any waiters I removed from the queue.
*/
dlist_foreach_modify(iter, &wakeup)
proclist_foreach_modify(iter, &wakeup, lwWaitLink)
{
PGPROC *waiter = dlist_container(PGPROC, lwWaitLink, iter.cur);
PGPROC *waiter = GetPGProcByNumber(iter.cur);
dlist_delete(&waiter->lwWaitLink);
proclist_delete(&wakeup, iter.cur, lwWaitLink);
/* check comment in LWLockWakeup() about this barrier */
pg_write_barrier();
waiter->lwWaiting = false;