Struct Runtime

pub struct Runtime { /* private fields */ }

The salsa runtime stores the storage for all queries as well as tracking the query stack and dependencies between cycles.

Each new runtime you create (e.g., via Runtime::new or Runtime::default) will have an independent set of query storage associated with it. Normally, therefore, you only do this once, at the start of your application.

Implementations

impl Runtime

pub fn new() -> Self

Create a new runtime; equivalent to Self::default. This is used when creating a new database.

pub fn synthetic_write(&mut self, durability: Durability)

A “synthetic write” causes the system to act as though some input of durability durability has changed. This is mostly useful for profiling scenarios, but it also has interactions with garbage collection. In general, a synthetic write to durability level D will cause the system to fully trace all queries of durability level D and below. When running a GC, then:

• Synthetic writes will cause more derived values to be retained. This is because derived values are only retained if they are traced, and a synthetic write can cause more things to be traced.
• Synthetic writes can cause more interned values to be collected. This is because interned values can only be collected if they were not yet traced in the current revision. Therefore, if you issue a synthetic write, execute some query Q, and then start collecting interned values, you will be able to recycle interned values not used in Q.

In general, then, one can do a “full GC” that retains only those things that are used by some query Q by (a) doing a synthetic write at Durability::HIGH, (b) executing the query Q and then (c) doing a sweep.

WARNING: Just like an ordinary write, this method triggers cancellation. If you invoke it while a snapshot exists, it will block until that snapshot is dropped – if that snapshot is owned by the current thread, this could trigger deadlock.

pub fn id(&self) -> RuntimeId

The unique identifier attached to this SalsaRuntime. Each snapshotted runtime has a distinct identifier.

pub fn active_query(&self) -> Option<DatabaseKeyIndex>

Returns the database-key for the query that this thread is actively executing (if any).

pub fn is_current_revision_canceled(&self) -> bool

Check if the current revision is canceled. If this method ever returns true, the currently executing query is also marked as having an untracked read – this means that, in the next revision, we will always recompute its value “as if” some input had changed. This means that, if your revision is canceled (which indicates that current query results will be ignored) your query is free to shortcircuit and return whatever it likes.

This method is useful for implementing cancellation of queries. You can do it in one of two ways, via Results or via unwinding.

The Result approach looks like this:

• Some queries invoke is_current_revision_canceled and return a special value, like Err(Canceled), if it returns true.
• Other queries propagate the special value using ? operator.
• API around top-level queries checks if the result is Ok or Err(Canceled).

The panic approach works in a similar way:

• Some queries invoke is_current_revision_canceled and panic with a special value, like Canceled, if it returns true.
• The implementation of Database trait overrides on_propagated_panic to throw this special value as well. This way, panic gets propagated naturally through dependant queries, even across the threads.
• API around top-level queries converts a panic into Result by catching the panic (using either std::panic::catch_unwind or threads) and downcasting the payload to Canceled (re-raising panic if downcast fails).

Note that salsa is explicitly designed to be panic-safe, so cancellation via unwinding is 100% valid approach to cancellation.

pub fn report_untracked_read(&self)

Reports that the query depends on some state unknown to salsa.

Queries which report untracked reads will be re-executed in the next revision.

pub fn report_synthetic_read(&self, durability: Durability)

Acts as though the current query had read an input with the given durability; this will force the current query’s durability to be at most durability.

This is mostly useful to control the durability level for on-demand inputs.

Trait Implementations

impl Debug for Runtime

fn fmt(&self, fmt: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Runtime

fn default() -> Self

Returns the “default value” for a type.