lock

tinystore lock hold runs a command while it holds a key of a lock, so that the command never runs twice at once: a cron job on two machines that share a store's server, or a deploy step two shells may start together.

tinystore lock ./data hold cron nightly-backup -- ./backup.sh

#Run a command under a lock

tinystore lock ./data hold cron nightly-backup -- ./backup.sh
tinystore lock ./data hold cron nightly-backup --wait 0 -- ./backup.sh

• The words are the lock, the key, and after -- the command with its own arguments. -- keeps the command's flags from being read as lock's.
• --wait 30s stands in line for the key that long, ten seconds when not given, as the SDKs' hold does. --wait 0 takes the key only if it is free. A key held by another past the wait exits 1, and the command never runs:

tinystore lock hold: lock cron: key nightly-backup is held by another; --wait stands in line longer

• The command gets the lease's fence in TINYSTORE_FENCE: a number larger than every earlier holder's, which a write can compare to refuse a holder that stalled. See Fences.
• lock hold ends with the command's exit code, once it has let the key go.

#The lease

The key is held through the server that holds the directory, or a sidecar lock hold starts, with a lease that lasts --ttl, 30 seconds when not given. lock hold renews it every third of --ttl while the command runs.

• A lease that is lost, revoked at --max-hold or not renewed in time because the server went away, stops the command, since another may hold the key now, and exits 1. On Linux and macOS the command gets SIGTERM, then SIGKILL five seconds later; a script that starts other programs should exec the last one, or trap TERM and stop them. On Windows it is ended at once.

tinystore lock hold: the lease was lost, so the command was stopped: another may hold the key now

• --max-hold 1h lets the key go an hour after it was given, however it was renewed.
• If lock hold itself is killed, the key is free once the lease runs out, --ttl after its last renewal.
• Locks live in the memory of the process that holds the store, so every holder must reach the same server (NOT-03).

#See also

• Locks: locks and semaphores from a program, waiting, leases and fences.