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Comment:Fix a problem in the memdb vfs xLock() function allowing clients to upgrade to EXCLUSIVE locks when other connections are holding SHARED. Forum post 5adb92e2baca3678.
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SHA3-256: 15f0be8a640e7bfa4130edd4650a745337bd96083b119a1553f9abf9ff066806
User & Date: dan 2022-12-05 14:12:14
Original Comment: Fix a problem in the memdb vfs xLock() function allowing clients to upgrade to EXCLUSIVE locks when other connections are holding SHARED.
References
2022-12-07
16:58
Streamline and improve testing of the locking in the memdb VFS. Follow-on to [15f0be8a640e7bfa]. (check-in: d71a0837 user: drh tags: trunk)
Context
2022-12-05
14:23
Fix a problem in the memdb vfs xLock() function allowing clients to upgrade to EXCLUSIVE locks when other connections are holding SHARED. (check-in: d18cce37 user: drh tags: branch-3.40)
14:20
Add test case that should have been part of previous commit. (check-in: dc7dd2d3 user: dan tags: trunk)
14:12
Fix a problem in the memdb vfs xLock() function allowing clients to upgrade to EXCLUSIVE locks when other connections are holding SHARED. Forum post 5adb92e2baca3678. (check-in: 15f0be8a user: dan tags: trunk)
13:07
Remove SQLITE_EXPERIMENTAL tag from sqlite3_vtab_collation() and fix a related doc typo. (check-in: 35d670b3 user: stephan tags: trunk)
Changes
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Changes to src/memdb.c.

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static int memdbLock(sqlite3_file *pFile, int eLock){
  MemFile *pThis = (MemFile*)pFile;
  MemStore *p = pThis->pStore;
  int rc = SQLITE_OK;
  if( eLock==pThis->eLock ) return SQLITE_OK;
  memdbEnter(p);
  if( eLock>SQLITE_LOCK_SHARED ){

    if( p->mFlags & SQLITE_DESERIALIZE_READONLY ){
      rc = SQLITE_READONLY;










    }else if( pThis->eLock<=SQLITE_LOCK_SHARED ){


      if( p->nWrLock ){
        rc = SQLITE_BUSY;
      }else{
        p->nWrLock = 1;
      }
    }
  }else if( eLock==SQLITE_LOCK_SHARED ){








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static int memdbLock(sqlite3_file *pFile, int eLock){
  MemFile *pThis = (MemFile*)pFile;
  MemStore *p = pThis->pStore;
  int rc = SQLITE_OK;
  if( eLock==pThis->eLock ) return SQLITE_OK;
  memdbEnter(p);
  if( eLock>SQLITE_LOCK_SHARED ){
    assert( pThis->eLock>=SQLITE_LOCK_SHARED );
    if( p->mFlags & SQLITE_DESERIALIZE_READONLY ){
      rc = SQLITE_READONLY;
    }else if( eLock==SQLITE_LOCK_EXCLUSIVE ){
      /* Taking an EXCLUSIVE lock. Fail if we only have SHARED and any
      ** other client has any kind of write-lock. Also fail if any other
      ** client is holding read-lock. */
      if( pThis->eLock<=SQLITE_LOCK_SHARED && p->nWrLock ){
        rc = SQLITE_BUSY;
      }else if( p->nRdLock>1 ){
        rc = SQLITE_BUSY;
      }
      p->nWrLock = 1;
    }else if( pThis->eLock<=SQLITE_LOCK_SHARED ){
      /* Upgrading to RESERVED or PENDING from SHARED. Fail if any other
      ** client has a write-lock of any kind.  */
      if( p->nWrLock ){
        rc = SQLITE_BUSY;
      }else{
        p->nWrLock = 1;
      }
    }
  }else if( eLock==SQLITE_LOCK_SHARED ){
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