MutableSnapshot

public open class MutableSnapshot
internal constructor(
    snapshotId: SnapshotId,
    invalid: SnapshotIdSet,
    override val readObserver: ((Any) -> Unit)?,
    override val writeObserver: ((Any) -> Unit)?,
) : Snapshot(snapshotId, invalid)

A snapshot of the values return by mutable states and other state objects. All state object will have the same value in the snapshot as they had when the snapshot was created unless they are explicitly changed in the snapshot.

To enter a snapshot call enter. The snapshot is the current snapshot as returned by currentSnapshot until the control returns from the lambda (or until a nested enter is called. All state objects will return the values associated with this snapshot, locally in the thread, until enter returns. All other threads are unaffected.

All changes made in a MutableSnapshot are snapshot isolated from all other snapshots and their changes can only be seen globally, or by new shots, after MutableSnapshot.apply as been called.

Snapshots can be nested by calling takeNestedSnapshot or MutableSnapshot.takeNestedMutableSnapshot.

Functions

public open fun takeNestedMutableSnapshot(
        readObserver: ((Any) -> Unit)? = null,
        writeObserver: ((Any) -> Unit)? = null,
    ): MutableSnapshot

Take a mutable snapshot of the state values in this snapshot. Entering this snapshot by calling enter allows state objects to be modified that are not visible to the this, the parent snapshot, until the apply is called.

Applying a nested snapshot, by calling apply, applies its change to, this, the parent snapshot. For a change to be visible globally, all the parent snapshots need to be applied until the root snapshot is applied to the global state.

All nested snapshots need to be disposed by calling dispose before resources associated with this snapshot can be collected. Nested active snapshots are still valid after the parent has been disposed but calling apply will fail.

public open fun apply(): SnapshotApplyResult

Apply the changes made to state objects in this snapshot to the global state, or to the parent snapshot if this is a nested mutable snapshot.

Once this method returns all changes made to this snapshot are atomically visible as the global state of the state object or to the parent snapshot.

While a snapshot is active (after it is created but before apply or dispose is called) requires resources to track the values in the snapshot. Once a snapshot is no longer needed it should be either applied by calling apply or disposed by calling dispose. A snapshot that has been had is apply called can also have dispose called on it. However, calling apply after calling dispose will throw an exception.

Leaving a snapshot active could cause hard to diagnose memory leaks values are maintained by state objects for unneeded snapshots. Take care to always call dispose on any snapshot.

Companion Object