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31d0a1dd0c
This patch adds a "row_locker" class providing locking (shard-locally) of individual clustering rows or entire partitions, and both exclusive and shared locks (a.k.a. reader/writer lock). As we'll see in a following patch, we need this locking capability for materialized views, to serialize the read-modify-update modifications which involve the same rows or partitions. The new row_locker is significantly different from the existing cell_locker. The two main differences are that 1. row_locker also supports locking the entire partition, not just individual rows (or cells in them), and that 2. row_locker supports also shared (reader) locks, not just exclusive locks. For this reason we opted for a new implementation, instead of making large modificiations to the existing cell_locker. And we put the source files in the view/ directory, because row_locker's requirements are pretty specific to the needs of materialized views. Signed-off-by: Nadav Har'El <nyh@scylladb.com>