Multiple Position Blocks

If an application using the BTRV function has two active position blocks on the same file and issues a read with a multiple record lock for the same record from both position blocks, both receive a successful status. However, when attempting to unlock the record with either a Key Number of -1 and the position in the Data Buffer or with a Key Number of -2, the record is unlocked only if both position blocks issue the unlock calls. If only one position block makes the unlock call (it does not matter which one), another user receives a Status Code 84 upon trying to lock the record. After both position blocks issue the unlock, the second user can lock the record.

This behavior is also true with single record locks, although the unlock command in this case does not require a specific Key Number and position in the Data Buffer. However, both position blocks still must issue the unlock in order for another user to lock the record.

Each cursor (that is, each position block) gets a lock. The MicroKernel allows cursors of the same client to lock the same record, but each cursor must issue an unlock before the record is completely unlocked.