1 files changed, 70 insertions, 41 deletions

diff --git a/src/os_unix.c b/src/os_unix.c
index c9b59f229..0eb2d5b00 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -4255,6 +4255,7 @@ struct unixShmNode {
   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 */
+  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 */
@@ -4796,6 +4797,38 @@ shmpage_out:
 }
 
 /*
+** Check that the pShmNode->aLock[] array comports with the locking bitmasks
+** held by each client. Return true if it does, or false otherwise. This
+** is to be used in an assert(). e.g.
+**
+**     assert( assertLockingArrayOk(pShmNode) );
+*/
+#ifdef SQLITE_DEBUG
+static int assertLockingArrayOk(unixShmNode *pShmNode){
+  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){
+    int i;
+    for(i=0; i<SQLITE_SHM_NLOCK; i++){
+      if( pX->exclMask & (1<<i) ){
+        assert( aLock[i]==0 );
+        aLock[i] = -1;
+      }else if( pX->sharedMask & (1<<i) ){
+        assert( aLock[i]>=0 );
+        aLock[i]++;
+      }
+    }
+  }
+
+  assert( 0==memcmp(pShmNode->aLock, aLock, sizeof(aLock)) );
+  return (memcmp(pShmNode->aLock, aLock, sizeof(aLock))==0);
+}
+#endif
+
+/*
 ** Change the lock state for a shared-memory segment.
 **
 ** Note that the relationship between SHAREd and EXCLUSIVE locks is a little
@@ -4811,10 +4844,10 @@ static int unixShmLock(
 ){
   unixFile *pDbFd = (unixFile*)fd;      /* Connection holding shared memory */
   unixShm *p = pDbFd->pShm;             /* The shared memory being locked */
-  unixShm *pX;                          /* For looping over all siblings */
   unixShmNode *pShmNode = p->pShmNode;  /* The underlying file iNode */
   int rc = SQLITE_OK;                   /* Result code */
   u16 mask;                             /* Mask of locks to take or release */
+  int *aLock = pShmNode->aLock;
 
   assert( pShmNode==pDbFd->pInode->pShmNode );
   assert( pShmNode->pInode==pDbFd->pInode );
@@ -4853,21 +4886,25 @@ static int unixShmLock(
   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 ){
-    u16 allMask = 0; /* Mask of locks held by siblings */
+    int ii;
+    int bUnlock = 1;
 
-    /* See if any siblings hold this same lock */
-    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
-      if( pX==p ) continue;
-      assert( (pX->exclMask & (p->exclMask|p->sharedMask))==0 );
-      allMask |= pX->sharedMask;
+    for(ii=ofst; ii<ofst+n; ii++){
+      if( aLock[ii]>((p->sharedMask & (1<<ii)) ? 1 : 0) ){
+        bUnlock = 0;
+      }
     }
 
-    /* Unlock the system-level locks */
-    if( (mask & allMask)==0 ){
+    if( bUnlock ){
       rc = unixShmSystemLock(pDbFd, F_UNLCK, ofst+UNIX_SHM_BASE, n);
-    }else{
-      rc = SQLITE_OK;
+      if( rc==SQLITE_OK ){
+        memset(&aLock[ofst], 0, sizeof(int)*n);
+      }
+    }else if( p->sharedMask & (1<<ofst) ){
+      assert( n==1 && aLock[ofst]>1 );
+      aLock[ofst]--;
     }
 
     /* Undo the local locks */
@@ -4876,55 +4913,47 @@ static int unixShmLock(
       p->sharedMask &= ~mask;
     } 
   }else if( flags & SQLITE_SHM_SHARED ){
-    u16 allShared = 0;  /* Union of locks held by connections other than "p" */
-
-    /* Find out which shared locks are already held by sibling connections.
-    ** If any sibling already holds an exclusive lock, go ahead and return
-    ** SQLITE_BUSY.
-    */
-    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
-      if( (pX->exclMask & mask)!=0 ){
+    assert( n==1 );
+    assert( (p->exclMask & (1<<ofst))==0 );
+    if( (p->sharedMask & mask)==0 ){
+      if( aLock[ofst]<0 ){
         rc = SQLITE_BUSY;
-        break;
-      }
-      allShared |= pX->sharedMask;
-    }
-
-    /* Get shared locks at the system level, if necessary */
-    if( rc==SQLITE_OK ){
-      if( (allShared & mask)==0 ){
+      }else if( aLock[ofst]==0 ){
         rc = unixShmSystemLock(pDbFd, F_RDLCK, ofst+UNIX_SHM_BASE, n);
-      }else{
-        rc = SQLITE_OK;
       }
-    }
 
-    /* Get the local shared locks */
-    if( rc==SQLITE_OK ){
-      p->sharedMask |= mask;
+      /* Get the local shared locks */
+      if( rc==SQLITE_OK ){
+        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.
-    */
-    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
-      if( (pX->exclMask & mask)!=0 || (pX->sharedMask & mask)!=0 ){
+    ** lock.  If any do, return SQLITE_BUSY right away.  */
+    int ii;
+    for(ii=ofst; ii<ofst+n; ii++){
+      assert( (p->sharedMask & mask)==0 );
+      if( (p->exclMask & (1<<ii))==0 && aLock[ii] ){
         rc = SQLITE_BUSY;
         break;
       }
     }
-  
-    /* Get the exclusive locks at the system level.  Then if successful
-    ** also mark the local connection as being locked.
-    */
+
+    /* 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);
       if( rc==SQLITE_OK ){
         assert( (p->sharedMask & mask)==0 );
         p->exclMask |= mask;
+        for(ii=ofst; ii<ofst+n; ii++){
+          aLock[ii] = -1;
+        }
       }
     }
   }
+  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));