octez-libs 20.1 · OCaml Package

Persistent data manager.

Every data read/write operation is protected by a mutex preventing concurrent data-races.

type 'a file = private {

encoding : 'a Data_encoding.t;
eq : 'a -> 'a -> bool;
path : string;
json : bool;

}

A data structure that represents files via their paths and encodings.

type 'a eq := 'a -> 'a -> bool

type 'a t

The type for the (persistent) data of a file.

type Tezos_error_monad.Error_monad.error +=

| Missing_stored_data of string

This error is returned when the requested data is not found.

val make_file : 
  ?json:bool ->
  filepath:string ->
  'a Data_encoding.t ->
  'a eq ->
  'a file

make_file ?(json=false) ~filepath encoding represents a file located at filepath. The content of this value is encoded using encoding. By default, the content is encoded in binary content except if json=true. eq is used internally to test whether the contents of the file should be updated when calling write or update_with.

Warning It is the caller responsability to ensure that the base directory of the filepath exists; otherwise, reading and writing will fail.

val get : 'a t -> 'a Lwt.t

get data accesses the data (cached).

val write : 'a t -> 'a -> unit Tezos_error_monad.Error_monad.tzresult Lwt.t

write data value overwrites the previous data with the new value. The cache is only updated if the write succeeds. If the write fails, it is up to the user to retry.

val write_file : 
  'a file ->
  'a ->
  unit Tezos_error_monad.Error_monad.tzresult Lwt.t

write_file encoded_file value raw writes the encoded_file with the value.

Warning this function should not be used in a normal context as it aims to overwrite the target without avoiding data races. Favour the usage of write.

val update_with : 
  'a t ->
  ('a -> 'a Lwt.t) ->
  unit Tezos_error_monad.Error_monad.tzresult Lwt.t

update_with data f atomically updates data with the result of the application of f. Concurrent accesses to the data will block until the value is updated.

The cache is only updated if the write succeeds. If the write fails, it is up to the user to retry.

Warning Calling read/write in f will result in a deadlock.

val load : 'a file -> 'a t Tezos_error_monad.Error_monad.tzresult Lwt.t

load encoded_file loads and decode a data from an encoded_file.

val init : 
  'a file ->
  initial_data:'a ->
  'a t Tezos_error_monad.Error_monad.tzresult Lwt.t

init encoded_file eq ~initial_data creates or load an on-disk data. If the file already exists, then the data is read from the file. Otherwise, initial_data is used.

package octez-libs