if (pcxt->nworkers == 0)
return;
+ /* We need to be a lock group leader. */
+ BecomeLockGroupLeader();
+
/* If we do have workers, we'd better have a DSM segment. */
Assert(pcxt->seg != NULL);
* backend-local state to match the original backend.
*/
+ /*
+ * Join locking group. We must do this before anything that could try
+ * to acquire a heavyweight lock, because any heavyweight locks acquired
+ * to this point could block either directly against the parallel group
+ * leader or against some process which in turn waits for a lock that
+ * conflicts with the parallel group leader, causing an undetected
+ * deadlock. (If we can't join the lock group, the leader has gone away,
+ * so just exit quietly.)
+ */
+ if (!BecomeLockGroupMember(fps->parallel_master_pgproc,
+ fps->parallel_master_pid))
+ return;
+
/*
* Load libraries that were loaded by original backend. We want to do
* this before restoring GUCs, because the libraries might define custom
#include "access/transam.h"
#include "access/twophase.h"
#include "access/twophase_rmgr.h"
+#include "access/xact.h"
#include "access/xlog.h"
#include "miscadmin.h"
#include "pg_trace.h"
lockMethodTable = LockMethods[lockmethodid];
if (lockmode <= 0 || lockmode > lockMethodTable->numLockModes)
elog(ERROR, "unrecognized lock mode: %d", lockmode);
+ Assert(!IsInParallelMode() || MyProc->lockGroupLeader != NULL);
if (RecoveryInProgress() && !InRecovery &&
(locktag->locktag_type == LOCKTAG_OBJECT ||
{
uint32 partition = LockHashPartition(hashcode);
+ /*
+ * It might seem unsafe to access proclock->groupLeader without a lock,
+ * but it's not really. Either we are initializing a proclock on our
+ * own behalf, in which case our group leader isn't changing because
+ * the group leader for a process can only ever be changed by the
+ * process itself; or else we are transferring a fast-path lock to the
+ * main lock table, in which case that process can't change it's lock
+ * group leader without first releasing all of its locks (and in
+ * particular the one we are currently transferring).
+ */
+ proclock->groupLeader = proc->lockGroupLeader != NULL ?
+ proc->lockGroupLeader : proc;
proclock->holdMask = 0;
proclock->releaseMask = 0;
/* Add proclock to appropriate lists */
* NOTES:
* Here's what makes this complicated: one process's locks don't
* conflict with one another, no matter what purpose they are held for
- * (eg, session and transaction locks do not conflict).
- * So, we must subtract off our own locks when determining whether the
- * requested new lock conflicts with those already held.
+ * (eg, session and transaction locks do not conflict). Nor do the locks
+ * of one process in a lock group conflict with those of another process in
+ * the same group. So, we must subtract off these locks when determining
+ * whether the requested new lock conflicts with those already held.
*/
int
LockCheckConflicts(LockMethod lockMethodTable,
{
int numLockModes = lockMethodTable->numLockModes;
LOCKMASK myLocks;
- LOCKMASK otherLocks;
+ int conflictMask = lockMethodTable->conflictTab[lockmode];
+ int conflictsRemaining[MAX_LOCKMODES];
+ int totalConflictsRemaining = 0;
int i;
+ SHM_QUEUE *procLocks;
+ PROCLOCK *otherproclock;
/*
* first check for global conflicts: If no locks conflict with my request,
* type of lock that conflicts with request. Bitwise compare tells if
* there is a conflict.
*/
- if (!(lockMethodTable->conflictTab[lockmode] & lock->grantMask))
+ if (!(conflictMask & lock->grantMask))
{
PROCLOCK_PRINT("LockCheckConflicts: no conflict", proclock);
return STATUS_OK;
}
/*
- * Rats. Something conflicts. But it could still be my own lock. We have
- * to construct a conflict mask that does not reflect our own locks, but
- * only lock types held by other processes.
+ * Rats. Something conflicts. But it could still be my own lock, or
+ * a lock held by another member of my locking group. First, figure out
+ * how many conflicts remain after subtracting out any locks I hold
+ * myself.
*/
myLocks = proclock->holdMask;
- otherLocks = 0;
for (i = 1; i <= numLockModes; i++)
{
- int myHolding = (myLocks & LOCKBIT_ON(i)) ? 1 : 0;
+ if ((conflictMask & LOCKBIT_ON(i)) == 0)
+ {
+ conflictsRemaining[i] = 0;
+ continue;
+ }
+ conflictsRemaining[i] = lock->granted[i];
+ if (myLocks & LOCKBIT_ON(i))
+ --conflictsRemaining[i];
+ totalConflictsRemaining += conflictsRemaining[i];
+ }
- if (lock->granted[i] > myHolding)
- otherLocks |= LOCKBIT_ON(i);
+ /* If no conflicts remain, we get the lock. */
+ if (totalConflictsRemaining == 0)
+ {
+ PROCLOCK_PRINT("LockCheckConflicts: resolved (simple)", proclock);
+ return STATUS_OK;
+ }
+
+ /* If no group locking, it's definitely a conflict. */
+ if (proclock->groupLeader == MyProc && MyProc->lockGroupLeader == NULL)
+ {
+ Assert(proclock->tag.myProc == MyProc);
+ PROCLOCK_PRINT("LockCheckConflicts: conflicting (simple)",
+ proclock);
+ return STATUS_FOUND;
}
/*
- * now check again for conflicts. 'otherLocks' describes the types of
- * locks held by other processes. If one of these conflicts with the kind
- * of lock that I want, there is a conflict and I have to sleep.
+ * Locks held in conflicting modes by members of our own lock group are
+ * not real conflicts; we can subtract those out and see if we still have
+ * a conflict. This is O(N) in the number of processes holding or awaiting
+ * locks on this object. We could improve that by making the shared memory
+ * state more complex (and larger) but it doesn't seem worth it.
*/
- if (!(lockMethodTable->conflictTab[lockmode] & otherLocks))
+ procLocks = &(lock->procLocks);
+ otherproclock = (PROCLOCK *)
+ SHMQueueNext(procLocks, procLocks, offsetof(PROCLOCK, lockLink));
+ while (otherproclock != NULL)
{
- /* no conflict. OK to get the lock */
- PROCLOCK_PRINT("LockCheckConflicts: resolved", proclock);
- return STATUS_OK;
+ if (proclock != otherproclock &&
+ proclock->groupLeader == otherproclock->groupLeader &&
+ (otherproclock->holdMask & conflictMask) != 0)
+ {
+ int intersectMask = otherproclock->holdMask & conflictMask;
+
+ for (i = 1; i <= numLockModes; i++)
+ {
+ if ((intersectMask & LOCKBIT_ON(i)) != 0)
+ {
+ if (conflictsRemaining[i] <= 0)
+ elog(PANIC, "proclocks held do not match lock");
+ conflictsRemaining[i]--;
+ totalConflictsRemaining--;
+ }
+ }
+
+ if (totalConflictsRemaining == 0)
+ {
+ PROCLOCK_PRINT("LockCheckConflicts: resolved (group)",
+ proclock);
+ return STATUS_OK;
+ }
+ }
+ otherproclock = (PROCLOCK *)
+ SHMQueueNext(procLocks, &otherproclock->lockLink,
+ offsetof(PROCLOCK, lockLink));
}
- PROCLOCK_PRINT("LockCheckConflicts: conflicting", proclock);
+ /* Nope, it's a real conflict. */
+ PROCLOCK_PRINT("LockCheckConflicts: conflicting (group)", proclock);
return STATUS_FOUND;
}
PROCLOCKTAG proclocktag;
int partition;
+ /* Can't prepare a lock group follower. */
+ Assert(MyProc->lockGroupLeader == NULL ||
+ MyProc->lockGroupLeader == MyProc);
+
/* This is a critical section: any error means big trouble */
START_CRIT_SECTION();
proclocktag.myLock = lock;
proclocktag.myProc = newproc;
+ /*
+ * Update groupLeader pointer to point to the new proc. (We'd
+ * better not be a member of somebody else's lock group!)
+ */
+ Assert(proclock->groupLeader == proclock->tag.myProc);
+ proclock->groupLeader = newproc;
+
/*
* Update the proclock. We should not find any existing entry for
* the same hash key, since there can be only one entry for any
*/
if (!found)
{
+ Assert(proc->lockGroupLeader == NULL);
+ proclock->groupLeader = proc;
proclock->holdMask = 0;
proclock->releaseMask = 0;
/* Add proclock to appropriate lists */
MyProc->backendLatestXid = InvalidTransactionId;
pg_atomic_init_u32(&MyProc->nextClearXidElem, INVALID_PGPROCNO);
+ /* Check that group locking fields are in a proper initial state. */
+ Assert(MyProc->lockGroupLeaderIdentifier == 0);
+ Assert(MyProc->lockGroupLeader == NULL);
+ Assert(MyProc->lockGroupSize == 0);
+
/*
* Acquire ownership of the PGPROC's latch, so that we can use WaitLatch
* on it. That allows us to repoint the process latch, which so far
OwnLatch(&MyProc->procLatch);
SwitchToSharedLatch();
+ /* Check that group locking fields are in a proper initial state. */
+ Assert(MyProc->lockGroupLeaderIdentifier == 0);
+ Assert(MyProc->lockGroupLeader == NULL);
+ Assert(MyProc->lockGroupSize == 0);
+
/*
* We might be reusing a semaphore that belonged to a failed process. So
* be careful and reinitialize its value here. (This is not strictly
if (MyReplicationSlot != NULL)
ReplicationSlotRelease();
+ /* Detach from any lock group of which we are a member. */
+ if (MyProc->lockGroupLeader != NULL)
+ {
+ PGPROC *leader = MyProc->lockGroupLeader;
+
+ LWLockAcquire(leader->backendLock, LW_EXCLUSIVE);
+ Assert(leader->lockGroupSize > 0);
+ if (--leader->lockGroupSize == 0)
+ {
+ leader->lockGroupLeaderIdentifier = 0;
+ leader->lockGroupLeader = NULL;
+ if (leader != MyProc)
+ {
+ procgloballist = leader->procgloballist;
+
+ /* Leader exited first; return its PGPROC. */
+ SpinLockAcquire(ProcStructLock);
+ leader->links.next = (SHM_QUEUE *) *procgloballist;
+ *procgloballist = leader;
+ SpinLockRelease(ProcStructLock);
+ }
+ }
+ else if (leader != MyProc)
+ MyProc->lockGroupLeader = NULL;
+ LWLockRelease(leader->backendLock);
+ }
+
/*
* Reset MyLatch to the process local one. This is so that signal
* handlers et al can continue using the latch after the shared latch
procgloballist = proc->procgloballist;
SpinLockAcquire(ProcStructLock);
- /* Return PGPROC structure (and semaphore) to appropriate freelist */
- proc->links.next = (SHM_QUEUE *) *procgloballist;
- *procgloballist = proc;
+ /*
+ * If we're still a member of a locking group, that means we're a leader
+ * which has somehow exited before its children. The last remaining child
+ * will release our PGPROC. Otherwise, release it now.
+ */
+ if (proc->lockGroupLeader == NULL)
+ {
+ /* Since lockGroupLeader is NULL, lockGroupSize should be 0. */
+ Assert(proc->lockGroupSize == 0);
+
+ /* Return PGPROC structure (and semaphore) to appropriate freelist */
+ proc->links.next = (SHM_QUEUE *) *procgloballist;
+ *procgloballist = proc;
+ }
/* Update shared estimate of spins_per_delay */
ProcGlobal->spins_per_delay = update_spins_per_delay(ProcGlobal->spins_per_delay);
bool allow_autovacuum_cancel = true;
int myWaitStatus;
PGPROC *proc;
+ PGPROC *leader = MyProc->lockGroupLeader;
int i;
+ /*
+ * If group locking is in use, locks held my members of my locking group
+ * need to be included in myHeldLocks.
+ */
+ if (leader != NULL)
+ {
+ SHM_QUEUE *procLocks = &(lock->procLocks);
+ PROCLOCK *otherproclock;
+
+ otherproclock = (PROCLOCK *)
+ SHMQueueNext(procLocks, procLocks, offsetof(PROCLOCK, lockLink));
+ while (otherproclock != NULL)
+ {
+ if (otherproclock->groupLeader == leader)
+ myHeldLocks |= otherproclock->holdMask;
+ otherproclock = (PROCLOCK *)
+ SHMQueueNext(procLocks, &otherproclock->lockLink,
+ offsetof(PROCLOCK, lockLink));
+ }
+ }
+
/*
* Determine where to add myself in the wait queue.
*
proc = (PGPROC *) waitQueue->links.next;
for (i = 0; i < waitQueue->size; i++)
{
+ /*
+ * If we're part of the same locking group as this waiter, its
+ * locks neither conflict with ours nor contribute to aheadRequsts.
+ */
+ if (leader != NULL && leader == proc->lockGroupLeader)
+ {
+ proc = (PGPROC *) proc->links.next;
+ continue;
+ }
/* Must he wait for me? */
if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks)
{
SetLatch(&proc->procLatch);
}
}
+
+/*
+ * BecomeLockGroupLeader - designate process as lock group leader
+ *
+ * Once this function has returned, other processes can join the lock group
+ * by calling BecomeLockGroupMember.
+ */
+void
+BecomeLockGroupLeader(void)
+{
+ /* If we already did it, we don't need to do it again. */
+ if (MyProc->lockGroupLeader == MyProc)
+ return;
+
+ /* We had better not be a follower. */
+ Assert(MyProc->lockGroupLeader == NULL);
+
+ /* Create single-member group, containing only ourselves. */
+ LWLockAcquire(MyProc->backendLock, LW_EXCLUSIVE);
+ MyProc->lockGroupLeader = MyProc;
+ MyProc->lockGroupLeaderIdentifier = MyProcPid;
+ MyProc->lockGroupSize = 1;
+ LWLockRelease(MyProc->backendLock);
+}
+
+/*
+ * BecomeLockGroupMember - designate process as lock group member
+ *
+ * This is pretty straightforward except for the possibility that the leader
+ * whose group we're trying to join might exit before we manage to do so;
+ * and the PGPROC might get recycled for an unrelated process. To avoid
+ * that, we require the caller to pass the PID of the intended PGPROC as
+ * an interlock. Returns true if we successfully join the intended lock
+ * group, and false if not.
+ */
+bool
+BecomeLockGroupMember(PGPROC *leader, int pid)
+{
+ bool ok = false;
+
+ /* Group leader can't become member of group */
+ Assert(MyProc != leader);
+
+ /* PID must be valid. */
+ Assert(pid != 0);
+
+ /* Try to join the group. */
+ LWLockAcquire(leader->backendLock, LW_EXCLUSIVE);
+ if (leader->lockGroupLeaderIdentifier == pid)
+ {
+ ok = true;
+ leader->lockGroupSize++;
+ MyProc->lockGroupLeader = leader;
+ }
+ LWLockRelease(leader->backendLock);
+
+ return ok;
+}
PROCLOCKTAG tag; /* unique identifier of proclock object */
/* data */
+ PGPROC *groupLeader; /* group leader, or NULL if no lock group */
LOCKMASK holdMask; /* bitmask for lock types currently held */
LOCKMASK releaseMask; /* bitmask for lock types to be released */
SHM_QUEUE lockLink; /* list link in LOCK's list of proclocks */
* worker */
} DeadLockState;
-
/*
* The lockmgr's shared hash tables are partitioned to reduce contention.
* To determine which partition a given locktag belongs to, compute the tag's
bool fpVXIDLock; /* are we holding a fast-path VXID lock? */
LocalTransactionId fpLocalTransactionId; /* lxid for fast-path VXID
* lock */
+ /* Support for lock groups. */
+ int lockGroupLeaderIdentifier; /* MyProcPid, if I'm a leader */
+ PGPROC *lockGroupLeader; /* lock group leader, if I'm a follower */
+ int lockGroupSize; /* # of members, if I'm a leader */
};
/* NOTE: "typedef struct PGPROC PGPROC" appears in storage/lock.h. */
extern void ProcWaitForSignal(void);
extern void ProcSendSignal(int pid);
+extern void BecomeLockGroupLeader(void);
+extern bool BecomeLockGroupMember(PGPROC *leader, int pid);
+
#endif /* PROC_H */
projects / users / rhaas / postgres.git / commitdiff