StorageConnection.kt
/*
* Copyright 2022 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.datastore.core
/**
* StorageConnection provides a way to read and write a particular type <T> of data.
* StorageConnections are created from [Storage] objects.
*/
interface StorageConnection<T> : Closeable {
/**
* Creates a scope for reading to allow storage reads, and will try to obtain a read lock.
*
* @param block The block of code that is performed within this scope. Block will
* receive `locked` parameter which is true if the try lock succeeded.
*
* @throws IOException when there is an unrecoverable exception in reading.
*/
suspend fun <R> readScope(
block: suspend ReadScope<T>.(locked: Boolean) -> R
): R
/**
* Creates a write scope that guaranteed to only have one single writer, ensuring also
* that any reads within this scope have the most current data.
*
* @throws IOException when there is an unrecoverable exception in writing.
*/
suspend fun writeScope(block: suspend WriteScope<T>.() -> Unit)
/**
* Provides a coordinator to guarantee data consistency across multiple threads and processes.
*/
val coordinator: InterProcessCoordinator
}
/**
* The scope used for a read transaction.
*/
interface ReadScope<T> : Closeable {
/**
* Read the data <T> from the underlying storage.
*/
suspend fun readData(): T
}
/**
* The scope used for a write transaction.
*/
interface WriteScope<T> : ReadScope<T> {
/**
* Writes the data <T> to the underlying storage.
*/
suspend fun writeData(value: T)
}
/* Convenience method for opening a read scope, doing a single read, and closing the scope. */
suspend fun <T> StorageConnection<T>.readData(): T = readScope { readData() }
/* Convenience method for opening a write scope, doing a single write, and closing the scope. */
suspend fun <T> StorageConnection<T>.writeData(value: T) = writeScope { writeData(value) }