diff --git a/manifest b/manifest
index 2c1dd24..21392b6 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\sharmless\scompiler\swarnings\sin\sdebugging\scode.
-D 2023-11-17T12:22:42.597
+C When\sSQLITE_ENABLE_SETLK_TIMEOUT\sis\sdefined,\suse\sa\sseparate\smutex\sin\sos_unix.c\sfor\seach\sshm\slocking\sslot.
+D 2023-11-17T17:10:37.075
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -709,7 +709,7 @@
 F src/os_common.h 6c0eb8dd40ef3e12fe585a13e709710267a258e2c8dd1c40b1948a1d14582e06
 F src/os_kv.c 4d39e1f1c180b11162c6dc4aa8ad34053873a639bac6baae23272fc03349986a
 F src/os_setup.h 6011ad7af5db4e05155f385eb3a9b4470688de6f65d6166b8956e58a3d872107
-F src/os_unix.c f8a557ff5b387ec599e8b84b7341e5a45ebdd579da03788364a34b9a9567faeb
+F src/os_unix.c 1f6a930e8469b3709728690d089b55deb2fe605ba860941ddc21a2345e51bce4
 F src/os_win.c 4a50a154aeebc66a1f8fb79c1ff6dd5fe3d005556533361e0d460d41cb6a45a8
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 987ab3a2cd9065d62e9955474470ff733445e2357432a67e3d0f5a8f9313e334
@@ -2140,8 +2140,11 @@
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P a9443dbfbe25e588b4adddde664ddf482f19f71c704fbf356d49cf3a6135e7fb
-R dc0c90fa6e9a7208b4b533ec9a5980a8
-U drh
-Z 5cf7a41ba5c0eb3c7c4392bc0e2744d2
+P ce6a75622ea5bca517bc6613e738aa670c9e1dd863596220eded5c2379c616c7
+R 277be03c0e13cb54ac8c8a3d23aba815
+T *branch * unix-setlk-timeout-mutexes
+T *sym-unix-setlk-timeout-mutexes *
+T -sym-trunk *
+U dan
+Z 8cc8841ac15d12b07622be01120eb3c1
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 98bef54..5124df9 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-ce6a75622ea5bca517bc6613e738aa670c9e1dd863596220eded5c2379c616c7
\ No newline at end of file
+4098df9652d90f2d22d5591d915d672c5413471f7916223510ba6fd932bfdd36
\ No newline at end of file
diff --git a/src/os_unix.c b/src/os_unix.c
index 3171b41..82c81a4 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -4313,6 +4313,25 @@
 ** Either unixShmNode.pShmMutex must be held or unixShmNode.nRef==0 and
 ** unixMutexHeld() is true when reading or writing any other field
 ** in this structure.
+**
+** aLock[SQLITE_SHM_NLOCK]:
+**   This array records the various locks held by clients on each of the
+**   SQLITE_SHM_NLOCK slots. If the aLock[] entry is set to 0, then no
+**   locks are held by the process on this slot. If it is set to -1, then
+**   some client holds an EXCLUSIVE lock on the locking slot. If the aLock[]
+**   value is set to a positive value, then it is the number of shared 
+**   locks currently held on the slot.
+**
+** aMutex[SQLITE_SHM_NLOCK]:
+**   Normally, when SQLITE_ENABLE_SETLK_TIMEOUT is not defined, mutex 
+**   pShmMutex is used to protect the aLock[] array and the right to
+**   call fcntl() on unixShmNode.hShm to obtain or release locks.
+**
+**   If SQLITE_ENABLE_SETLK_TIMEOUT is defined though, we use an array
+**   of mutexes - one for each locking slot. To read or write locking
+**   slot aLock[iSlot], the caller must hold the corresponding mutex
+**   aMutex[iSlot]. Similarly, to call fcntl() to obtain or release a
+**   lock corresponding to slot iSlot, mutex aMutex[iSlot] must be held.
 */
 struct unixShmNode {
   unixInodeInfo *pInode;     /* unixInodeInfo that owns this SHM node */
@@ -4326,10 +4345,11 @@
   char **apRegion;           /* Array of mapped shared-memory regions */
   int nRef;                  /* Number of unixShm objects pointing to this */
   unixShm *pFirst;           /* All unixShm objects pointing to this */
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+  sqlite3_mutex *aMutex[SQLITE_SHM_NLOCK];
+#endif
   int aLock[SQLITE_SHM_NLOCK];  /* # shared locks on slot, -1==excl lock */
 #ifdef SQLITE_DEBUG
-  u8 exclMask;               /* Mask of exclusive locks held */
-  u8 sharedMask;             /* Mask of shared locks held */
   u8 nextShmId;              /* Next available unixShm.id value */
 #endif
 };
@@ -4412,16 +4432,29 @@
   struct flock f;        /* The posix advisory locking structure */
   int rc = SQLITE_OK;    /* Result code form fcntl() */
 
-  /* Access to the unixShmNode object is serialized by the caller */
   pShmNode = pFile->pInode->pShmNode;
-  assert( pShmNode->nRef==0 || sqlite3_mutex_held(pShmNode->pShmMutex) );
-  assert( pShmNode->nRef>0 || unixMutexHeld() );
+
+  /* Assert that the correct mutex or mutexes are held. */
+  if( pShmNode->nRef==0 ){
+    assert( ofst==UNIX_SHM_DMS && n==1 && unixMutexHeld() );
+  }else{
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+    int ii;
+    for(ii=ofst-UNIX_SHM_BASE; ii<ofst-UNIX_SHM_BASE+n; ii++){
+      assert( sqlite3_mutex_held(pShmNode->aMutex[ii]) );
+    }
+#else
+    assert( sqlite3_mutex_held(pShmNode->pShmMutex) );
+    assert( pShmNode->nRef>0 );
+#endif
+  }
 
   /* Shared locks never span more than one byte */
   assert( n==1 || lockType!=F_RDLCK );
 
   /* Locks are within range */
   assert( n>=1 && n<=SQLITE_SHM_NLOCK );
+  assert( ofst>=UNIX_SHM_BASE && ofst<=(UNIX_SHM_DMS+SQLITE_SHM_NLOCK) );
 
   if( pShmNode->hShm>=0 ){
     int res;
@@ -4440,39 +4473,28 @@
     }
   }
 
-  /* Update the global lock state and do debug tracing */
+  /* Do debug tracing */
 #ifdef SQLITE_DEBUG
-  { u16 mask;
   OSTRACE(("SHM-LOCK "));
-  mask = ofst>31 ? 0xffff : (1<<(ofst+n)) - (1<<ofst);
   if( rc==SQLITE_OK ){
     if( lockType==F_UNLCK ){
-      OSTRACE(("unlock %d ok", ofst));
-      pShmNode->exclMask &= ~mask;
-      pShmNode->sharedMask &= ~mask;
+      OSTRACE(("unlock %d..%d ok\n", ofst, ofst+n-1));
     }else if( lockType==F_RDLCK ){
-      OSTRACE(("read-lock %d ok", ofst));
-      pShmNode->exclMask &= ~mask;
-      pShmNode->sharedMask |= mask;
+      OSTRACE(("read-lock %d..%d ok\n", ofst, ofst+n-1));
     }else{
       assert( lockType==F_WRLCK );
-      OSTRACE(("write-lock %d ok", ofst));
-      pShmNode->exclMask |= mask;
-      pShmNode->sharedMask &= ~mask;
+      OSTRACE(("write-lock %d..%d ok\n", ofst, ofst+n-1));
     }
   }else{
     if( lockType==F_UNLCK ){
-      OSTRACE(("unlock %d failed", ofst));
+      OSTRACE(("unlock %d..%d failed\n", ofst, ofst+n-1));
     }else if( lockType==F_RDLCK ){
-      OSTRACE(("read-lock failed"));
+      OSTRACE(("read-lock %d..%d failed\n", ofst, ofst+n-1));
     }else{
       assert( lockType==F_WRLCK );
-      OSTRACE(("write-lock %d failed", ofst));
+      OSTRACE(("write-lock %d..%d failed\n", ofst, ofst+n-1));
     }
   }
-  OSTRACE((" - afterwards %03x,%03x\n",
-           pShmNode->sharedMask, pShmNode->exclMask));
-  }
 #endif
 
   return rc;      
@@ -4509,6 +4531,11 @@
     int i;
     assert( p->pInode==pFd->pInode );
     sqlite3_mutex_free(p->pShmMutex);
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+    for(i=0; i<SQLITE_SHM_NLOCK; i++){
+      sqlite3_mutex_free(p->aMutex[i]);
+    }
+#endif
     for(i=0; i<p->nRegion; i+=nShmPerMap){
       if( p->hShm>=0 ){
         osMunmap(p->apRegion[i], p->szRegion);
@@ -4689,6 +4716,18 @@
         rc = SQLITE_NOMEM_BKPT;
         goto shm_open_err;
       }
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+      {
+        int ii;
+        for(ii=0; ii<SQLITE_SHM_NLOCK; ii++){
+          pShmNode->aMutex[ii] = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
+          if( pShmNode->aMutex[ii]==0 ){
+            rc = SQLITE_NOMEM_BKPT;
+            goto shm_open_err;
+          }
+        }
+      }
+#endif
     }
 
     if( pInode->bProcessLock==0 ){
@@ -4910,9 +4949,11 @@
 */
 #ifdef SQLITE_DEBUG
 static int assertLockingArrayOk(unixShmNode *pShmNode){
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+  return 1;
+#else
   unixShm *pX;
   int aLock[SQLITE_SHM_NLOCK];
-  assert( sqlite3_mutex_held(pShmNode->pShmMutex) );
 
   memset(aLock, 0, sizeof(aLock));
   for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
@@ -4930,13 +4971,14 @@
 
   assert( 0==memcmp(pShmNode->aLock, aLock, sizeof(aLock)) );
   return (memcmp(pShmNode->aLock, aLock, sizeof(aLock))==0);
+#endif
 }
 #endif
 
 /*
 ** Change the lock state for a shared-memory segment.
 **
-** Note that the relationship between SHAREd and EXCLUSIVE locks is a little
+** Note that the relationship between SHARED and EXCLUSIVE locks is a little
 ** different here than in posix.  In xShmLock(), one can go from unlocked
 ** to shared and back or from unlocked to exclusive and back.  But one may
 ** not go from shared to exclusive or from exclusive to shared.
@@ -4951,7 +4993,7 @@
   unixShm *p;                           /* The shared memory being locked */
   unixShmNode *pShmNode;                /* The underlying file iNode */
   int rc = SQLITE_OK;                   /* Result code */
-  u16 mask;                             /* Mask of locks to take or release */
+  u16 mask = (1<<(ofst+n)) - (1<<ofst); /* Mask of locks to take or release */
   int *aLock;
 
   p = pDbFd->pShm;
@@ -4997,18 +5039,51 @@
   }
 #endif
 
-  mask = (1<<(ofst+n)) - (1<<ofst);
-  assert( n>1 || mask==(1<<ofst) );
-  sqlite3_mutex_enter(pShmNode->pShmMutex);
-  assert( assertLockingArrayOk(pShmNode) );
-  if( flags & SQLITE_SHM_UNLOCK ){
-    if( (p->exclMask|p->sharedMask) & mask ){
-      int ii;
-      int bUnlock = 1;
+  /* Check if there is any work to do. There are three cases:
+  **
+  **    a) An unlock operation where there are locks to unlock,
+  **    b) An shared lock where the requested lock is not already held
+  **    c) An exclusive lock where the requested lock is not already held
+  **
+  ** The SQLite core never requests an exclusive lock that it already holds.
+  ** This is assert()ed below.
+  */
+  assert( flags!=(SQLITE_SHM_EXCLUSIVE|SQLITE_SHM_LOCK) 
+       || 0==(p->exclMask & mask) 
+  );
+  if( ((flags & SQLITE_SHM_UNLOCK) && ((p->exclMask|p->sharedMask) & mask))
+   || (flags==(SQLITE_SHM_SHARED|SQLITE_SHM_LOCK) && 0==(p->sharedMask & mask))
+   || (flags==(SQLITE_SHM_EXCLUSIVE|SQLITE_SHM_LOCK))
+  ){
 
-      for(ii=ofst; ii<ofst+n; ii++){
-        if( aLock[ii]>((p->sharedMask & (1<<ii)) ? 1 : 0) ){
+    /* Take the required mutexes */
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+    int iMutex;
+    for(iMutex=ofst; iMutex<ofst+n; iMutex++){
+      sqlite3_mutex_enter(pShmNode->aMutex[iMutex]);
+    }
+#else
+    sqlite3_mutex_enter(pShmNode->pShmMutex);
+#endif
+
+    if( flags & SQLITE_SHM_UNLOCK ){
+      /* Case (a) - unlock.  */
+      int bUnlock = 1;
+      assert( (p->exclMask & p->sharedMask)==0 );
+      assert( (flags & SQLITE_SHM_EXCLUSIVE)==0 || (p->exclMask & mask)==mask );
+      assert( (flags & SQLITE_SHM_SHARED)==0 || (p->sharedMask & mask)==mask );
+
+      /* If this is a SHARED lock being unlocked, it is possible that other
+      ** clients within this process are holding the same SHARED lock. In
+      ** this case, set bUnlock to 0 so that the posix lock is not removed
+      ** from the file-descriptor below.  */
+      if( flags & SQLITE_SHM_SHARED ){
+        assert( n==1 );
+        assert( aLock[ofst]>=1 );
+        if( aLock[ofst]>1 ){
           bUnlock = 0;
+          aLock[ofst]--;
+          p->sharedMask &= ~mask;
         }
       }
 
@@ -5016,23 +5091,15 @@
         rc = unixShmSystemLock(pDbFd, F_UNLCK, ofst+UNIX_SHM_BASE, n);
         if( rc==SQLITE_OK ){
           memset(&aLock[ofst], 0, sizeof(int)*n);
+          p->sharedMask &= ~mask;
+          p->exclMask &= ~mask;
         }
-      }else if( ALWAYS(p->sharedMask & (1<<ofst)) ){
-        assert( n==1 && aLock[ofst]>1 );
-        aLock[ofst]--;
       }
+    }else if( flags & SQLITE_SHM_SHARED ){
+      /* Case (b) - a shared lock.  */
 
-      /* Undo the local locks */
-      if( rc==SQLITE_OK ){
-        p->exclMask &= ~mask;
-        p->sharedMask &= ~mask;
-      }
-    }
-  }else if( flags & SQLITE_SHM_SHARED ){
-    assert( n==1 );
-    assert( (p->exclMask & (1<<ofst))==0 );
-    if( (p->sharedMask & mask)==0 ){
       if( aLock[ofst]<0 ){
+        /* An exclusive lock is held by some other connection. BUSY. */ 
         rc = SQLITE_BUSY;
       }else if( aLock[ofst]==0 ){
         rc = unixShmSystemLock(pDbFd, F_RDLCK, ofst+UNIX_SHM_BASE, n);
@@ -5043,34 +5110,48 @@
         p->sharedMask |= mask;
         aLock[ofst]++;
       }
-    }
-  }else{
-    /* Make sure no sibling connections hold locks that will block this
-    ** lock.  If any do, return SQLITE_BUSY right away.  */
-    int ii;
-    for(ii=ofst; ii<ofst+n; ii++){
-      assert( (p->sharedMask & mask)==0 );
-      if( ALWAYS((p->exclMask & (1<<ii))==0) && aLock[ii] ){
-        rc = SQLITE_BUSY;
-        break;
-      }
-    }
+    }else{
+      /* Case (c) - an exclusive lock.  */
+      int ii;
 
-    /* Get the exclusive locks at the system level. Then if successful
-    ** also update the in-memory values. */
-    if( rc==SQLITE_OK ){
-      rc = unixShmSystemLock(pDbFd, F_WRLCK, ofst+UNIX_SHM_BASE, n);
+      assert( flags==(SQLITE_SHM_LOCK|SQLITE_SHM_EXCLUSIVE) );
+      assert( (p->sharedMask & mask)==0 );
+      assert( (p->exclMask & mask)==0 );
+
+      /* Make sure no sibling connections hold locks that will block this
+      ** lock.  If any do, return SQLITE_BUSY right away.  */
+      for(ii=ofst; ii<ofst+n; ii++){
+        if( aLock[ii] ){
+          rc = SQLITE_BUSY;
+          break;
+        }
+      }
+
+      /* Get the exclusive locks at the system level. Then if successful
+      ** also update the in-memory values. */
       if( rc==SQLITE_OK ){
-        assert( (p->sharedMask & mask)==0 );
-        p->exclMask |= mask;
-        for(ii=ofst; ii<ofst+n; ii++){
-          aLock[ii] = -1;
+        rc = unixShmSystemLock(pDbFd, F_WRLCK, ofst+UNIX_SHM_BASE, n);
+        if( rc==SQLITE_OK ){
+          p->exclMask |= mask;
+          for(ii=ofst; ii<ofst+n; ii++){
+            aLock[ii] = -1;
+          }
         }
       }
     }
+  
+    assert( assertLockingArrayOk(pShmNode) );
+
+    /* Drop the mutexes acquired above. */
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+    for(iMutex=ofst; iMutex<ofst+n; iMutex++){
+      sqlite3_mutex_leave(pShmNode->aMutex[iMutex]);
+    }
+#else
+    sqlite3_mutex_leave(pShmNode->pShmMutex);
+#endif
   }
-  assert( assertLockingArrayOk(pShmNode) );
-  sqlite3_mutex_leave(pShmNode->pShmMutex);
+
   OSTRACE(("SHM-LOCK shmid-%d, pid-%d got %03x,%03x\n",
            p->id, osGetpid(0), p->sharedMask, p->exclMask));
   return rc;