/*
* ReceiveSharedInvalidMessages
* Process shared-cache-invalidation messages waiting for this backend
*
* NOTE: it is entirely possible for this routine to be invoked recursively
* as a consequence of processing inside the invalFunction or resetFunction.
* Hence, we must be holding no SI resources when we call them. The only
* bad side-effect is that SIDelExpiredDataEntries might be called extra
* times on the way out of a nested call.
*/
void
ReceiveSharedInvalidMessages(
void (*invalFunction) (SharedInvalidationMessage *msg),
void (*resetFunction) (void))
{
SharedInvalidationMessage data;
int getResult;
bool gotMessage = false;
for (;;)
{
/*
* We can run SIGetDataEntry in parallel with other backends
* running SIGetDataEntry for themselves, since each instance will
* modify only fields of its own backend's ProcState, and no
* instance will look at fields of other backends' ProcStates. We
* express this by grabbing SInvalLock in shared mode. Note that
* this is not exactly the normal (read-only) interpretation of a
* shared lock! Look closely at the interactions before allowing
* SInvalLock to be grabbed in shared mode for any other reason!
*
* The routines later in this file that use shared mode are okay with
* this, because they aren't looking at the ProcState fields
* associated with SI message transfer; they only use the
* ProcState array as an easy way to find all the PGPROC
* structures.
*/
LWLockAcquire(SInvalLock, LW_SHARED);
getResult = SIGetDataEntry(shmInvalBuffer, MyBackendId, &data);
LWLockRelease(SInvalLock);
if (getResult == 0)
break; /* nothing more to do */
if (getResult < 0)
{
/* got a reset message */
elog(DEBUG4, "cache state reset");
resetFunction();
}
else
{
/* got a normal data message */
invalFunction(&data);
}
gotMessage = true;
}
/* If we got any messages, try to release dead messages */
if (gotMessage)
{
LWLockAcquire(SInvalLock, LW_EXCLUSIVE);
SIDelExpiredDataEntries(shmInvalBuffer);
LWLockRelease(SInvalLock);
}
}
/*
* ReceiveSharedInvalidMessages
* Process shared-cache-invalidation messages waiting for this backend
*
* NOTE: it is entirely possible for this routine to be invoked recursively
* as a consequence of processing inside the invalFunction or resetFunction.
* Hence, we must be holding no SI resources when we call them. The only
* bad side-effect is that SIDelExpiredDataEntries might be called extra
* times on the way out of a nested call.
*/
void
ReceiveSharedInvalidMessages(
void (*invalFunction) (SharedInvalidationMessage *msg),
void (*resetFunction) (void))
{
SharedInvalidationMessage data;
int getResult;
bool gotMessage = false;
for (;;)
{
/*
* We can discard any pending catchup event, since we will not exit
* this loop until we're fully caught up.
*/
catchupInterruptOccurred = 0;
/*
* We can run SIGetDataEntry in parallel with other backends running
* SIGetDataEntry for themselves, since each instance will modify only
* fields of its own backend's ProcState, and no instance will look at
* fields of other backends' ProcStates. We express this by grabbing
* SInvalLock in shared mode. Note that this is not exactly the
* normal (read-only) interpretation of a shared lock! Look closely at
* the interactions before allowing SInvalLock to be grabbed in shared
* mode for any other reason!
*/
LWLockAcquire(SInvalLock, LW_SHARED);
getResult = SIGetDataEntry(shmInvalBuffer, MyBackendId, &data);
LWLockRelease(SInvalLock);
if (getResult == 0)
break; /* nothing more to do */
if (getResult < 0)
{
/* got a reset message */
elog(DEBUG4, "cache state reset");
resetFunction();
}
else
{
/* got a normal data message */
invalFunction(&data);
}
gotMessage = true;
}
/* If we got any messages, try to release dead messages */
if (gotMessage)
{
LWLockAcquire(SInvalLock, LW_EXCLUSIVE);
SIDelExpiredDataEntries(shmInvalBuffer);
LWLockRelease(SInvalLock);
}
}
/*
* ReceiveSharedInvalidMessages
* Process shared-cache-invalidation messages waiting for this backend
*
* We guarantee to process all messages that had been queued before the
* routine was entered. It is of course possible for more messages to get
* queued right after our last SIGetDataEntries call.
*
* NOTE: it is entirely possible for this routine to be invoked recursively
* as a consequence of processing inside the invalFunction or resetFunction.
* Furthermore, such a recursive call must guarantee that all outstanding
* inval messages have been processed before it exits. This is the reason
* for the strange-looking choice to use a statically allocated buffer array
* and counters; it's so that a recursive call can process messages already
* sucked out of sinvaladt.c.
*/
void
ReceiveSharedInvalidMessages(
void (*invalFunction) (SharedInvalidationMessage *msg),
void (*resetFunction) (void))
{
#define MAXINVALMSGS 32
static SharedInvalidationMessage messages[MAXINVALMSGS];
/*
* We use volatile here to prevent bugs if a compiler doesn't realize that
* recursion is a possibility ...
*/
static volatile int nextmsg = 0;
static volatile int nummsgs = 0;
/* Deal with any messages still pending from an outer recursion */
while (nextmsg < nummsgs)
{
SharedInvalidationMessage *msg = &messages[nextmsg++];
invalFunction(msg);
}
do
{
int getResult;
nextmsg = nummsgs = 0;
/* Try to get some more messages */
getResult = SIGetDataEntries(messages, MAXINVALMSGS);
if (getResult < 0)
{
/* got a reset message */
elog(DEBUG4, "cache state reset");
resetFunction();
break; /* nothing more to do */
}
/* Process them, being wary that a recursive call might eat some */
nextmsg = 0;
nummsgs = getResult;
while (nextmsg < nummsgs)
{
SharedInvalidationMessage *msg = &messages[nextmsg++];
invalFunction(msg);
}
/*
* We only need to loop if the last SIGetDataEntries call (which might
* have been within a recursive call) returned a full buffer.
*/
} while (nummsgs == MAXINVALMSGS);
/*
* We are now caught up. If we received a catchup signal, reset that
* flag, and call SICleanupQueue(). This is not so much because we need
* to flush dead messages right now, as that we want to pass on the
* catchup signal to the next slowest backend. "Daisy chaining" the
* catchup signal this way avoids creating spikes in system load for what
* should be just a background maintenance activity.
*/
if (catchupInterruptOccurred)
{
catchupInterruptOccurred = 0;
elog(DEBUG4, "sinval catchup complete, cleaning queue");
SICleanupQueue(false, 0);
}
}