From ded1959120db41174d720fc3a157cc648694d6f9 Mon Sep 17 00:00:00 2001
From: dan <Dan Kennedy>
Date: Fri, 30 May 2025 20:52:18 +0000
Subject: If blocking locks are enabled, avoid using the busy handler when
 blocked by another process running recovery.

FossilOrigin-Name: a35236757ab57c4c9b34e47c5dbc10d8f1220f8152955f5303cf9c3902ee169b
---
 src/btree.c   | 5 ++---
 src/os_unix.c | 5 +++--
 src/pager.c   | 9 +++++++++
 src/wal.c     | 3 ++-
 4 files changed, 16 insertions(+), 6 deletions(-)

(limited to 'src')

diff --git a/src/btree.c b/src/btree.c
index 064856635..25a9b1b4a 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -3697,11 +3697,10 @@ static SQLITE_NOINLINE int btreeBeginTrans(
       (void)sqlite3PagerWalWriteLock(pPager, 0);
       unlockBtreeIfUnused(pBt);
     }
-#if defined(SQLITE_ENABLE_SETLK_TIMEOUT) && defined(SQLITE_ENABLE_SNAPSHOT)
+#if defined(SQLITE_ENABLE_SETLK_TIMEOUT)
     if( rc==SQLITE_BUSY_TIMEOUT ){
       /* If a blocking lock timed out, break out of the loop here so that
-      ** the busy-handler is not invoked. This can only happen when opening
-      ** a transaction on a snapshot. */
+      ** the busy-handler is not invoked.  */
       break;
     }
 #endif
diff --git a/src/os_unix.c b/src/os_unix.c
index 1146545fe..5bbd7ceb6 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -5043,13 +5043,14 @@ static int unixShmLock(
   ** occur later in the above list than the lock being obtained may be
   ** held.
   **
-  ** It is not permitted to block on the RECOVER lock.
+  ** It is not permitted to block on the RECOVER lock if any other
+  ** locks are held.
   */
 #if defined(SQLITE_ENABLE_SETLK_TIMEOUT) && defined(SQLITE_DEBUG)
   {
     u16 lockMask = (p->exclMask|p->sharedMask);
     assert( (flags & SQLITE_SHM_UNLOCK) || pDbFd->iBusyTimeout==0 || (
-          (ofst!=2)                                   /* not RECOVER */
+          (ofst!=2 || lockMask==0)  /* not RECOVER */
        && (ofst!=1 || lockMask==0 || lockMask==2)
        && (ofst!=0 || lockMask<3)
        && (ofst<3  || lockMask<(1<<ofst))
diff --git a/src/pager.c b/src/pager.c
index 21f3ac5f6..1850ba37b 100644
--- a/src/pager.c
+++ b/src/pager.c
@@ -700,6 +700,9 @@ struct Pager {
   Wal *pWal;                  /* Write-ahead log used by "journal_mode=wal" */
   char *zWal;                 /* File name for write-ahead log */
 #endif
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+  sqlite3 *dbWal;
+#endif
 };
 
 /*
@@ -7581,6 +7584,11 @@ static int pagerOpenWal(Pager *pPager){
         pPager->fd, pPager->zWal, pPager->exclusiveMode,
         pPager->journalSizeLimit, &pPager->pWal
     );
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+    if( rc==SQLITE_OK ){
+      sqlite3WalDb(pPager->pWal, pPager->dbWal);
+    }
+#endif
   }
   pagerFixMaplimit(pPager);
 
@@ -7700,6 +7708,7 @@ int sqlite3PagerWalWriteLock(Pager *pPager, int bLock){
 ** blocking locks are required.
 */
 void sqlite3PagerWalDb(Pager *pPager, sqlite3 *db){
+  pPager->dbWal = db;
   if( pagerUseWal(pPager) ){
     sqlite3WalDb(pPager->pWal, db);
   }
diff --git a/src/wal.c b/src/wal.c
index 5fe2296d6..fc176988b 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -3062,7 +3062,6 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
       rc = walIndexReadHdr(pWal, pChanged);
     }
 #ifdef SQLITE_ENABLE_SETLK_TIMEOUT
-    walDisableBlocking(pWal);
     if( rc==SQLITE_BUSY_TIMEOUT ){
       rc = SQLITE_BUSY;
       *pCnt |= WAL_RETRY_BLOCKED_MASK;
@@ -3077,6 +3076,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
       ** WAL_RETRY this routine will be called again and will probably be
       ** right on the second iteration.
       */
+      walEnableBlocking(pWal);
       if( pWal->apWiData[0]==0 ){
         /* This branch is taken when the xShmMap() method returns SQLITE_BUSY.
         ** We assume this is a transient condition, so return WAL_RETRY. The
@@ -3093,6 +3093,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
         rc = SQLITE_BUSY_RECOVERY;
       }
     }
+    walDisableBlocking(pWal);
     if( rc!=SQLITE_OK ){
       return rc;
     }
-- 
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