Module sp_runtime::offchain::storage_lock
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Off-chain Storage Lock
A storage-based lock with a defined expiry time.
The lock is using Local Storage and allows synchronizing access to critical
section of your code for concurrently running Off-chain Workers. Usage of
PERSISTENT variant of the storage persists the lock value across a full node
restart or re-orgs.
A use case for the lock is to make sure that a particular section of the code is only run by one Off-chain Worker at a time. This may include performing a side-effect (i.e. an HTTP call) or alteration of single or multiple Local Storage entries.
One use case would be collective updates of multiple data items or append / remove of i.e. sets, vectors which are stored in the off-chain storage DB.
Example:
// in your off-chain worker code
use sp_runtime::offchain::{
storage::StorageValueRef,
storage_lock::{StorageLock, Time},
};
fn append_to_in_storage_vec<'a, T>(key: &'a [u8], _: T) where T: Codec {
// `access::lock` defines the storage entry which is used for
// persisting the lock in the underlying database.
// The entry name _must_ be unique and can be interpreted as a
// unique mutex instance reference tag.
let mut lock = StorageLock::<Time>::new(b"access::lock");
{
let _guard = lock.lock();
let acc = StorageValueRef::persistent(key);
let v: Vec<T> = acc.get::<Vec<T>>().unwrap().unwrap();
// modify `v` as desired
// i.e. perform some heavy computation with
// side effects that should only be done once.
acc.set(&v);
// drop `_guard` implicitly at end of scope
}
}Structs
Lockable based on block number and timestamp.
A deadline based on block number and time.
Storage based lock.
RAII style guard for a lock.
Lockable based on the current timestamp with a configurable expiration time.
Traits
Bound for a block number source
used with BlockAndTime<BlockNumberProvider>.
Lockable item for use with a persisted storage lock.