worker_read_write_locks

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CREATE TABLE worker_read_write_locks (
    lock_name TEXT NOT NULL,
    lock_key TEXT NOT NULL,
    -- We write the instance name to ease manual debugging, we don't ever read
    -- from it.
    -- Note: instance names aren't guarenteed to be unique.
    instance_name TEXT NOT NULL,
    -- Whether the process has taken out a "read" or a "write" lock.
    write_lock BOOLEAN NOT NULL,
    -- A random string generated each time an instance takes out a lock. Used by
    -- the instance to tell whether the lock is still held by it (e.g. in the
    -- case where the process stalls for a long time the lock may time out and
    -- be taken out by another instance, at which point the original instance
    -- can tell it no longer holds the lock as the tokens no longer match).
    token TEXT NOT NULL,
    last_renewed_ts BIGINT NOT NULL,

    -- This constraint ensures that a given lock has only been acquired in read
    -- xor write mode, but not both.
    FOREIGN KEY (lock_name, lock_key, write_lock) REFERENCES worker_read_write_locks_mode (lock_name, lock_key, write_lock)
);
CREATE UNIQUE INDEX worker_read_write_locks_key ON worker_read_write_locks (lock_name, lock_key, token);
CREATE UNIQUE INDEX worker_read_write_locks_write ON worker_read_write_locks (lock_name, lock_key) WHERE write_lock;