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Remove volatile qualifiers from dynahash.c, shmem.c, and sinvaladt.c 

Prior to commit 0709b7ee72, access to
variables within a spinlock-protected critical section had to be done
through a volatile pointer, but that should no longer be necessary.

Thomas Munro
This commit is contained in:
Robert Haas 2015-10-16 14:12:20 -04:00
parent 78652a3332
commit 430008b5a7
3 changed files with 37 additions and 55 deletions
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11
src/backend/storage/ipc/shmem.c
View File

@ -170,29 +170,26 @@ ShmemAlloc(Size size)
Size newFree;
void *newSpace;
/* use volatile pointer to prevent code rearrangement */
volatile PGShmemHeader *shmemseghdr = ShmemSegHdr;
/*
* ensure all space is adequately aligned.
*/
size = MAXALIGN(size);
Assert(shmemseghdr != NULL);
Assert(ShmemSegHdr != NULL);
SpinLockAcquire(ShmemLock);
newStart = shmemseghdr->freeoffset;
newStart = ShmemSegHdr->freeoffset;
/* extra alignment for large requests, since they are probably buffers */
if (size >= BLCKSZ)
newStart = BUFFERALIGN(newStart);
newFree = newStart + size;
if (newFree <= shmemseghdr->totalsize)
if (newFree <= ShmemSegHdr->totalsize)
{
newSpace = (void *) ((char *) ShmemBase + newStart);
shmemseghdr->freeoffset = newFree;
ShmemSegHdr->freeoffset = newFree;
}
else
newSpace = NULL;

22
src/backend/storage/ipc/sinvaladt.c
View File

@ -485,14 +485,9 @@ SIInsertDataEntries(const SharedInvalidationMessage *data, int n)
}
/* Update current value of maxMsgNum using spinlock */
{
/* use volatile pointer to prevent code rearrangement */
volatile SISeg *vsegP = segP;
SpinLockAcquire(&vsegP->msgnumLock);
vsegP->maxMsgNum = max;
SpinLockRelease(&vsegP->msgnumLock);
}
SpinLockAcquire(&segP->msgnumLock);
segP->maxMsgNum = max;
SpinLockRelease(&segP->msgnumLock);
/*
* Now that the maxMsgNum change is globally visible, we give everyone
@ -579,14 +574,9 @@ SIGetDataEntries(SharedInvalidationMessage *data, int datasize)
stateP->hasMessages = false;
/* Fetch current value of maxMsgNum using spinlock */
{
/* use volatile pointer to prevent code rearrangement */
volatile SISeg *vsegP = segP;
SpinLockAcquire(&vsegP->msgnumLock);
max = vsegP->maxMsgNum;
SpinLockRelease(&vsegP->msgnumLock);
}
SpinLockAcquire(&segP->msgnumLock);
max = segP->maxMsgNum;
SpinLockRelease(&segP->msgnumLock);
if (stateP->resetState)
{

59
src/backend/utils/hash/dynahash.c
View File

@ -941,25 +941,22 @@ hash_search_with_hash_value(HTAB *hashp,
case HASH_REMOVE:
if (currBucket != NULL)
{
/* use volatile pointer to prevent code rearrangement */
volatile HASHHDR *hctlv = hctl;
/* if partitioned, must lock to touch nentries and freeList */
if (IS_PARTITIONED(hctlv))
SpinLockAcquire(&hctlv->mutex);
if (IS_PARTITIONED(hctl))
SpinLockAcquire(&hctl->mutex);
Assert(hctlv->nentries > 0);
hctlv->nentries--;
Assert(hctl->nentries > 0);
hctl->nentries--;
/* remove record from hash bucket's chain. */
*prevBucketPtr = currBucket->link;
/* add the record to the freelist for this table. */
currBucket->link = hctlv->freeList;
hctlv->freeList = currBucket;
currBucket->link = hctl->freeList;
hctl->freeList = currBucket;
if (IS_PARTITIONED(hctlv))
SpinLockRelease(&hctlv->mutex);
if (IS_PARTITIONED(hctl))
SpinLockRelease(&hctl->mutex);
/*
* better hope the caller is synchronizing access to this
@ -1180,26 +1177,25 @@ hash_update_hash_key(HTAB *hashp,
static HASHBUCKET
get_hash_entry(HTAB *hashp)
{
/* use volatile pointer to prevent code rearrangement */
volatile HASHHDR *hctlv = hashp->hctl;
HASHHDR *hctl = hashp->hctl;
HASHBUCKET newElement;
for (;;)
{
/* if partitioned, must lock to touch nentries and freeList */
if (IS_PARTITIONED(hctlv))
SpinLockAcquire(&hctlv->mutex);
if (IS_PARTITIONED(hctl))
SpinLockAcquire(&hctl->mutex);
/* try to get an entry from the freelist */
newElement = hctlv->freeList;
newElement = hctl->freeList;
if (newElement != NULL)
break;
/* no free elements. allocate another chunk of buckets */
if (IS_PARTITIONED(hctlv))
SpinLockRelease(&hctlv->mutex);
if (IS_PARTITIONED(hctl))
SpinLockRelease(&hctl->mutex);
if (!element_alloc(hashp, hctlv->nelem_alloc))
if (!element_alloc(hashp, hctl->nelem_alloc))
{
/* out of memory */
return NULL;
@ -1207,11 +1203,11 @@ get_hash_entry(HTAB *hashp)
}
/* remove entry from freelist, bump nentries */
hctlv->freeList = newElement->link;
hctlv->nentries++;
hctl->freeList = newElement->link;
hctl->nentries++;
if (IS_PARTITIONED(hctlv))
SpinLockRelease(&hctlv->mutex);
if (IS_PARTITIONED(hctl))
SpinLockRelease(&hctl->mutex);
return newElement;
}
@ -1536,8 +1532,7 @@ seg_alloc(HTAB *hashp)
static bool
element_alloc(HTAB *hashp, int nelem)
{
/* use volatile pointer to prevent code rearrangement */
volatile HASHHDR *hctlv = hashp->hctl;
HASHHDR *hctl = hashp->hctl;
Size elementSize;
HASHELEMENT *firstElement;
HASHELEMENT *tmpElement;
@ -1548,7 +1543,7 @@ element_alloc(HTAB *hashp, int nelem)
return false;
/* Each element has a HASHELEMENT header plus user data. */
elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(hctlv->entrysize);
elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(hctl->entrysize);
CurrentDynaHashCxt = hashp->hcxt;
firstElement = (HASHELEMENT *) hashp->alloc(nelem * elementSize);
@ -1567,15 +1562,15 @@ element_alloc(HTAB *hashp, int nelem)
}
/* if partitioned, must lock to touch freeList */
if (IS_PARTITIONED(hctlv))
SpinLockAcquire(&hctlv->mutex);
if (IS_PARTITIONED(hctl))
SpinLockAcquire(&hctl->mutex);
/* freelist could be nonempty if two backends did this concurrently */
firstElement->link = hctlv->freeList;
hctlv->freeList = prevElement;
firstElement->link = hctl->freeList;
hctl->freeList = prevElement;
if (IS_PARTITIONED(hctlv))
SpinLockRelease(&hctlv->mutex);
if (IS_PARTITIONED(hctl))
SpinLockRelease(&hctl->mutex);
return true;
}