Use dlists instead of SHM_QUEUE for predicate locking

Part of a series to remove SHM_QUEUE. ilist.h style lists are more widely used
and have an easier to use interface.

Reviewed-by: Thomas Munro <thomas.munro@gmail.com> (in an older version)
Discussion: https://postgr.es/m/20221120055930.t6kl3tyivzhlrzu2@awork3.anarazel.de
Discussion: https://postgr.es/m/20200211042229.msv23badgqljrdg2@alap3.anarazel.de

src/include/storage/predicate_internals.h

@@ -14,6 +14,7 @@
 #ifndef PREDICATE_INTERNALS_H
 #define PREDICATE_INTERNALS_H
 
+#include "lib/ilist.h"
 #include "storage/lock.h"
 #include "storage/lwlock.h"
 
@@ -84,13 +85,14 @@ typedef struct SERIALIZABLEXACT
 		SerCommitSeqNo lastCommitBeforeSnapshot;	/* when not committed or
 													 * no conflict out */
 	}			SeqNo;
-	SHM_QUEUE	outConflicts;	/* list of write transactions whose data we
+	dlist_head	outConflicts;	/* list of write transactions whose data we
 								 * couldn't read. */
-	SHM_QUEUE	inConflicts;	/* list of read transactions which couldn't
+	dlist_head	inConflicts;	/* list of read transactions which couldn't
 								 * see our write. */
-	SHM_QUEUE	predicateLocks; /* list of associated PREDICATELOCK objects */
+	dlist_head	predicateLocks; /* list of associated PREDICATELOCK objects */
-	SHM_QUEUE	finishedLink;	/* list link in
+	dlist_node	finishedLink;	/* list link in
 								 * FinishedSerializableTransactions */
+	dlist_node	xactLink;		/* PredXact->activeList/availableList */
 
 	/*
 	 * perXactPredicateListLock is only used in parallel queries: it protects
@@ -103,7 +105,7 @@ typedef struct SERIALIZABLEXACT
 	 * for r/o transactions: list of concurrent r/w transactions that we could
 	 * potentially have conflicts with, and vice versa for r/w transactions
 	 */
-	SHM_QUEUE	possibleUnsafeConflicts;
+	dlist_head	possibleUnsafeConflicts;
 
 	TransactionId topXid;		/* top level xid for the transaction, if one
 								 * exists; else invalid */
@@ -139,28 +141,10 @@ typedef struct SERIALIZABLEXACT
  */
 #define SXACT_FLAG_PARTIALLY_RELEASED	0x00000800
 
-/*
- * The following types are used to provide an ad hoc list for holding
- * SERIALIZABLEXACT objects.  An HTAB is overkill, since there is no need to
- * access these by key -- there are direct pointers to these objects where
- * needed.  If a shared memory list is created, these types can probably be
- * eliminated in favor of using the general solution.
- */
-typedef struct PredXactListElementData
-{
-	SHM_QUEUE	link;
-	SERIALIZABLEXACT sxact;
-}			PredXactListElementData;
-
-typedef struct PredXactListElementData *PredXactListElement;
-
-#define PredXactListElementDataSize \
-		((Size)MAXALIGN(sizeof(PredXactListElementData)))
-
 typedef struct PredXactListData
 {
-	SHM_QUEUE	availableList;
+	dlist_head	availableList;
-	SHM_QUEUE	activeList;
+	dlist_head	activeList;
 
 	/*
 	 * These global variables are maintained when registering and cleaning up
@@ -187,7 +171,7 @@ typedef struct PredXactListData
 												 * seq no */
 	SERIALIZABLEXACT *OldCommittedSxact;	/* shared copy of dummy sxact */
 
-	PredXactListElement element;
+	SERIALIZABLEXACT *element;
 }			PredXactListData;
 
 typedef struct PredXactListData *PredXactList;
@@ -208,8 +192,8 @@ typedef struct PredXactListData *PredXactList;
  */
 typedef struct RWConflictData
 {
-	SHM_QUEUE	outLink;		/* link for list of conflicts out from a sxact */
+	dlist_node	outLink;		/* link for list of conflicts out from a sxact */
-	SHM_QUEUE	inLink;			/* link for list of conflicts in to a sxact */
+	dlist_node	inLink;			/* link for list of conflicts in to a sxact */
 	SERIALIZABLEXACT *sxactOut;
 	SERIALIZABLEXACT *sxactIn;
 }			RWConflictData;
@@ -221,7 +205,7 @@ typedef struct RWConflictData *RWConflict;
 
 typedef struct RWConflictPoolHeaderData
 {
-	SHM_QUEUE	availableList;
+	dlist_head	availableList;
 	RWConflict	element;
 }			RWConflictPoolHeaderData;
 
@@ -303,7 +287,7 @@ typedef struct PREDICATELOCKTARGET
 	PREDICATELOCKTARGETTAG tag; /* unique identifier of lockable object */
 
 	/* data */
-	SHM_QUEUE	predicateLocks; /* list of PREDICATELOCK objects assoc. with
+	dlist_head	predicateLocks; /* list of PREDICATELOCK objects assoc. with
 								 * predicate lock target */
 } PREDICATELOCKTARGET;
 
@@ -336,9 +320,9 @@ typedef struct PREDICATELOCK
 	PREDICATELOCKTAG tag;		/* unique identifier of lock */
 
 	/* data */
-	SHM_QUEUE	targetLink;		/* list link in PREDICATELOCKTARGET's list of
+	dlist_node	targetLink;		/* list link in PREDICATELOCKTARGET's list of
 								 * predicate locks */
-	SHM_QUEUE	xactLink;		/* list link in SERIALIZABLEXACT's list of
+	dlist_node	xactLink;		/* list link in SERIALIZABLEXACT's list of
 								 * predicate locks */
 	SerCommitSeqNo commitSeqNo; /* only used for summarized predicate locks */
 } PREDICATELOCK;