diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 40de84e934ed28a49ba2dcb4e15f5ca893b56c60..ad3e87271816e8773b3832480d0a0eb0be65d4b8 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -390,7 +390,6 @@ MarkAsPreparing(TransactionId xid, const char *gid,
proc->roleId = owner;
proc->lwWaiting = false;
proc->lwWaitMode = 0;
- proc->lwWaitLink = NULL;
proc->waitLock = NULL;
proc->waitProcLock = NULL;
for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 43f4d6b6534bc46de60762c1e8c1bce165069688..d9d704461b7aebb97f2f7192ff46e36a828a6d78 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -117,9 +117,9 @@ inline static void
PRINT_LWDEBUG(const char *where, const LWLock *lock)
{
if (Trace_lwlocks)
- elog(LOG, "%s(%s %d): excl %d shared %d head %p rOK %d",
+ elog(LOG, "%s(%s %d): excl %d shared %d rOK %d",
where, T_NAME(lock), T_ID(lock),
- (int) lock->exclusive, lock->shared, lock->head,
+ (int) lock->exclusive, lock->shared,
(int) lock->releaseOK);
}
@@ -479,8 +479,7 @@ LWLockInitialize(LWLock *lock, int tranche_id)
lock->exclusive = 0;
lock->shared = 0;
lock->tranche = tranche_id;
- lock->head = NULL;
- lock->tail = NULL;
+ dlist_init(&lock->waiters);
}
@@ -619,12 +618,7 @@ LWLockAcquireCommon(LWLock *lock, LWLockMode mode, uint64 *valptr, uint64 val)
proc->lwWaiting = true;
proc->lwWaitMode = mode;
- proc->lwWaitLink = NULL;
- if (lock->head == NULL)
- lock->head = proc;
- else
- lock->tail->lwWaitLink = proc;
- lock->tail = proc;
+ dlist_push_head(&lock->waiters, &proc->lwWaitLink);
/* Can release the mutex now */
SpinLockRelease(&lock->mutex);
@@ -840,12 +834,7 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
proc->lwWaiting = true;
proc->lwWaitMode = LW_WAIT_UNTIL_FREE;
- proc->lwWaitLink = NULL;
- if (lock->head == NULL)
- lock->head = proc;
- else
- lock->tail->lwWaitLink = proc;
- lock->tail = proc;
+ dlist_push_head(&lock->waiters, &proc->lwWaitLink);
/* Can release the mutex now */
SpinLockRelease(&lock->mutex);
@@ -1002,10 +991,7 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
proc->lwWaiting = true;
proc->lwWaitMode = LW_WAIT_UNTIL_FREE;
/* waiters are added to the front of the queue */
- proc->lwWaitLink = lock->head;
- if (lock->head == NULL)
- lock->tail = proc;
- lock->head = proc;
+ dlist_push_head(&lock->waiters, &proc->lwWaitLink);
/*
* Set releaseOK, to make sure we get woken up as soon as the lock is
@@ -1087,9 +1073,10 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
void
LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
{
- PGPROC *head;
- PGPROC *proc;
- PGPROC *next;
+ dlist_head wakeup;
+ dlist_mutable_iter iter;
+
+ dlist_init(&wakeup);
/* Acquire mutex. Time spent holding mutex should be short! */
SpinLockAcquire(&lock->mutex);
@@ -1104,24 +1091,16 @@ 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.
*/
- head = lock->head;
-
- if (head != NULL && head->lwWaitMode == LW_WAIT_UNTIL_FREE)
+ dlist_foreach_modify(iter, &lock->waiters)
{
- proc = head;
- next = proc->lwWaitLink;
- while (next && next->lwWaitMode == LW_WAIT_UNTIL_FREE)
- {
- proc = next;
- next = next->lwWaitLink;
- }
+ PGPROC *waiter = dlist_container(PGPROC, lwWaitLink, iter.cur);
+
+ if (waiter->lwWaitMode != LW_WAIT_UNTIL_FREE)
+ break;
- /* proc is now the last PGPROC to be released */
- lock->head = next;
- proc->lwWaitLink = NULL;
+ dlist_delete(&waiter->lwWaitLink);
+ dlist_push_tail(&wakeup, &waiter->lwWaitLink);
}
- else
- head = NULL;
/* We are done updating shared state of the lock itself. */
SpinLockRelease(&lock->mutex);
@@ -1129,15 +1108,14 @@ LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
/*
* Awaken any waiters I removed from the queue.
*/
- while (head != NULL)
+ dlist_foreach_modify(iter, &wakeup)
{
- proc = head;
- head = proc->lwWaitLink;
- proc->lwWaitLink = NULL;
+ PGPROC *waiter = dlist_container(PGPROC, lwWaitLink, iter.cur);
+ dlist_delete(&waiter->lwWaitLink);
/* check comment in LWLockRelease() about this barrier */
pg_write_barrier();
- proc->lwWaiting = false;
- PGSemaphoreUnlock(&proc->sem);
+ waiter->lwWaiting = false;
+ PGSemaphoreUnlock(&waiter->sem);
}
}
@@ -1148,10 +1126,12 @@ LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
void
LWLockRelease(LWLock *lock)
{
- PGPROC *head;
- PGPROC *proc;
+ dlist_head wakeup;
+ dlist_mutable_iter iter;
int i;
+ dlist_init(&wakeup);
+
PRINT_LWDEBUG("LWLockRelease", lock);
/*
@@ -1187,58 +1167,39 @@ LWLockRelease(LWLock *lock)
* if someone has already awakened waiters that haven't yet acquired the
* lock.
*/
- head = lock->head;
- if (head != NULL)
+ if (lock->exclusive == 0 && lock->shared == 0 && lock->releaseOK)
{
- if (lock->exclusive == 0 && lock->shared == 0 && lock->releaseOK)
+ /*
+ * Remove the to-be-awakened PGPROCs from the queue.
+ */
+ bool releaseOK = true;
+ bool wokeup_somebody = false;
+
+ dlist_foreach_modify(iter, &lock->waiters)
{
- /*
- * Remove the to-be-awakened PGPROCs from the queue.
- */
- bool releaseOK = true;
+ PGPROC *waiter = dlist_container(PGPROC, lwWaitLink, iter.cur);
- proc = head;
+ if (wokeup_somebody && waiter->lwWaitMode == LW_EXCLUSIVE)
+ continue;
- /*
- * First wake up any backends that want to be woken up without
- * acquiring the lock.
- */
- while (proc->lwWaitMode == LW_WAIT_UNTIL_FREE && proc->lwWaitLink)
- proc = proc->lwWaitLink;
+ dlist_delete(&waiter->lwWaitLink);
+ dlist_push_tail(&wakeup, &waiter->lwWaitLink);
/*
- * If the front waiter wants exclusive lock, awaken him only.
- * Otherwise awaken as many waiters as want shared access.
+ * Prevent additional wakeups until retryer gets to
+ * run. Backends that are just waiting for the lock to become
+ * free don't retry automatically.
*/
- if (proc->lwWaitMode != LW_EXCLUSIVE)
+ if (waiter->lwWaitMode != LW_WAIT_UNTIL_FREE)
{
- while (proc->lwWaitLink != NULL &&
- proc->lwWaitLink->lwWaitMode != LW_EXCLUSIVE)
- {
- if (proc->lwWaitMode != LW_WAIT_UNTIL_FREE)
- releaseOK = false;
- proc = proc->lwWaitLink;
- }
- }
- /* proc is now the last PGPROC to be released */
- lock->head = proc->lwWaitLink;
- proc->lwWaitLink = NULL;
-
- /*
- * Prevent additional wakeups until retryer gets to run. Backends
- * that are just waiting for the lock to become free don't retry
- * automatically.
- */
- if (proc->lwWaitMode != LW_WAIT_UNTIL_FREE)
releaseOK = false;
+ wokeup_somebody = true;
+ }
- lock->releaseOK = releaseOK;
- }
- else
- {
- /* lock is still held, can't awaken anything */
- head = NULL;
+ if(waiter->lwWaitMode == LW_EXCLUSIVE)
+ break;
}
+ lock->releaseOK = releaseOK;
}
/* We are done updating shared state of the lock itself. */
@@ -1249,13 +1210,12 @@ LWLockRelease(LWLock *lock)
/*
* Awaken any waiters I removed from the queue.
*/
- while (head != NULL)
+ dlist_foreach_modify(iter, &wakeup)
{
+ PGPROC *waiter = dlist_container(PGPROC, lwWaitLink, iter.cur);
LOG_LWDEBUG("LWLockRelease", T_NAME(lock), T_ID(lock),
"release waiter");
- proc = head;
- head = proc->lwWaitLink;
- proc->lwWaitLink = NULL;
+ dlist_delete(&waiter->lwWaitLink);
/*
* Guarantee that lwWaiting being unset only becomes visible once the
* unlink from the link has completed. Otherwise the target backend
@@ -1267,8 +1227,8 @@ LWLockRelease(LWLock *lock)
* another lock.
*/
pg_write_barrier();
- proc->lwWaiting = false;
- PGSemaphoreUnlock(&proc->sem);
+ waiter->lwWaiting = false;
+ PGSemaphoreUnlock(&waiter->sem);
}
/*
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index ea88a241443f393995fc1a316f13cc41ae270af3..a4789fcdc87a9cbf253892b98be9e3bae75c1883 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -372,7 +372,6 @@ InitProcess(void)
MyPgXact->vacuumFlags |= PROC_IS_AUTOVACUUM;
MyProc->lwWaiting = false;
MyProc->lwWaitMode = 0;
- MyProc->lwWaitLink = NULL;
MyProc->waitLock = NULL;
MyProc->waitProcLock = NULL;
#ifdef USE_ASSERT_CHECKING
@@ -535,7 +534,6 @@ InitAuxiliaryProcess(void)
MyPgXact->vacuumFlags = 0;
MyProc->lwWaiting = false;
MyProc->lwWaitMode = 0;
- MyProc->lwWaitLink = NULL;
MyProc->waitLock = NULL;
MyProc->waitProcLock = NULL;
#ifdef USE_ASSERT_CHECKING
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 09654a873e3ded3c170cdbf327c0d7f598722b25..c84970a7add8c51c99cd3de75c163d5a41f352d8 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -14,6 +14,7 @@
#ifndef LWLOCK_H
#define LWLOCK_H
+#include "lib/ilist.h"
#include "storage/s_lock.h"
struct PGPROC;
@@ -50,9 +51,7 @@ typedef struct LWLock
char exclusive; /* # of exclusive holders (0 or 1) */
int shared; /* # of shared holders (0..MaxBackends) */
int tranche; /* tranche ID */
- struct PGPROC *head; /* head of list of waiting PGPROCs */
- struct PGPROC *tail; /* tail of list of waiting PGPROCs */
- /* tail is undefined when head is NULL */
+ dlist_head waiters; /* list of waiting PGPROCs */
} LWLock;
/*
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 4ad4164927ecd76f3250438b48c1c0e05287b7b9..e868f0cd9f1e0486a7659b5e8ff669d44fa457e2 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -15,6 +15,7 @@
#define _PROC_H_
#include "access/xlogdefs.h"
+#include "lib/ilist.h"
#include "storage/latch.h"
#include "storage/lock.h"
#include "storage/pg_sema.h"
@@ -104,7 +105,7 @@ struct PGPROC
/* Info about LWLock the process is currently waiting for, if any. */
bool lwWaiting; /* true if waiting for an LW lock */
uint8 lwWaitMode; /* lwlock mode being waited for */
- struct PGPROC *lwWaitLink; /* next waiter for same LW lock */
+ dlist_node lwWaitLink; /* position in LW lock wait list */
/* Info about lock the process is currently waiting for, if any. */
/* waitLock and waitProcLock are NULL if not currently waiting. */