Fixes to ensure SQLITE_ENABLE_SETLK_TIMEOUT builds use a blocking lock and do not call xSleep() when (a) opening a snapshot transaction, and (b) when blocked by another process running recovery.

FossilOrigin-Name: 7f9c0cdd0630a41db359b188b226a1ad6a3bae1663c27169acfe25edc7fb171b

5 files changed, 32 insertions, 13 deletions

diff --git a/src/btree.c b/src/btree.c
index c85491c7d..f53060e7f 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -3698,6 +3698,13 @@ static SQLITE_NOINLINE int btreeBeginTrans(
       (void)sqlite3PagerWalWriteLock(pPager, 0);
       unlockBtreeIfUnused(pBt);
     }
+#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.  */
+      break;
+    }
+#endif
   }while( (rc&0xFF)==SQLITE_BUSY && pBt->inTransaction==TRANS_NONE &&
           btreeInvokeBusyHandler(pBt) );
   sqlite3PagerWalDb(pPager, 0);
diff --git a/src/os_unix.c b/src/os_unix.c
index 1146545fe..784bc3517 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -5035,21 +5035,20 @@ static int unixShmLock(
   /* Check that, if this to be a blocking lock, no locks that occur later
   ** in the following list than the lock being obtained are already held:
   **
-  **   1. Checkpointer lock (ofst==1).
-  **   2. Write lock (ofst==0).
-  **   3. Read locks (ofst>=3 && ofst<SQLITE_SHM_NLOCK).
+  **   1. Recovery lock (ofst==2).
+  **   2. Checkpointer lock (ofst==1).
+  **   3. Write lock (ofst==0).
+  **   4. Read locks (ofst>=3 && ofst<SQLITE_SHM_NLOCK).
   **
   ** In other words, if this is a blocking lock, none of the locks that
   ** occur later in the above list than the lock being obtained may be
   ** held.
-  **
-  ** It is not permitted to block on the RECOVER lock.
   */
 #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)
        && (ofst!=1 || lockMask==0 || lockMask==2)
        && (ofst!=0 || lockMask<3)
        && (ofst<3  || lockMask<(1<<ofst))
diff --git a/src/os_win.c b/src/os_win.c
index cd7e49190..c7c923e77 100644
--- a/src/os_win.c
+++ b/src/os_win.c
@@ -2722,7 +2722,11 @@ static int winHandleLockTimeout(
       if( res==WAIT_OBJECT_0 ){
         ret = TRUE;
       }else if( res==WAIT_TIMEOUT ){
+#if SQLITE_ENABLE_SETLK_TIMEOUT==1
         rc = SQLITE_BUSY_TIMEOUT;
+#else
+        rc = SQLITE_BUSY;
+#endif
       }else{
         /* Some other error has occurred */
         rc = SQLITE_IOERR_LOCK;
@@ -4533,21 +4537,20 @@ static int winShmLock(
   /* Check that, if this to be a blocking lock, no locks that occur later
   ** in the following list than the lock being obtained are already held:
   **
-  **   1. Checkpointer lock (ofst==1).
-  **   2. Write lock (ofst==0).
-  **   3. Read locks (ofst>=3 && ofst<SQLITE_SHM_NLOCK).
+  **   1. Recovery lock (ofst==2).
+  **   2. Checkpointer lock (ofst==1).
+  **   3. Write lock (ofst==0).
+  **   4. Read locks (ofst>=3 && ofst<SQLITE_SHM_NLOCK).
   **
   ** In other words, if this is a blocking lock, none of the locks that
   ** occur later in the above list than the lock being obtained may be
   ** held.
-  **
-  ** It is not permitted to block on the RECOVER lock.
   */
 #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)
        && (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;
     }