com.spotify.flo

Interface EvalContext

All Known Implementing Classes:

AsyncContext, EvalContextWithTask, ForwardingEvalContext, InstrumentedContext, MemoizingContext, OverridingContext, PersistingContext, SyncContext, TracingContext

public interface EvalContext

A context for controlling Task evaluation and EvalContext.Value computation.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	EvalContext.Promise<T> A promise for a EvalContext.Value that is supposed to be EvalContext.Promise.set(Object).
static interface	EvalContext.Value<T> A wrapped value with additional semantics for how the enclosed value becomes available and how computations on that value are executed.

Field Summary

Fields

Modifier and Type	Field and Description
static org.slf4j.Logger	LOG

Method Summary

Modifier and Type	Method and Description
static EvalContext	async(Executor executor) Create an asynchronous EvalContext that executes all evaluation on the given Executor.
default Optional<Task<?>>	currentTask() When called during the evaluation of a task, this method will return the Task currently being processed.
default <T> EvalContext.Value<T>	evaluate(Task<T> task) The entry point for evaluating a EvalContext.Value from a Task.
default <T> EvalContext.Value<T>	evaluateInternal(Task<T> task, EvalContext context) A variant of evaluate(Task) that allows the caller to specify the EvalContext that should be used within the graph during evaluation.
default <T> EvalContext.Value<T>	immediateValue(T value) Create a EvalContext.Value with semantics defined by this EvalContext
default <T> EvalContext.Value<T>	invokeProcessFn(TaskId taskId, Fn<T> processFn) Invoke the process function of a task.
default TaskOperator.Listener	listener() Used to report task metadata.
<T> EvalContext.Promise<T>	promise() Create a promise for a value that can be fulfilled somewhere else.
static EvalContext	sync() Create a default, synchronous EvalContext.
<T> EvalContext.Value<T>	value(Fn<T> value) Create a EvalContext.Value with semantics defined by this EvalContext

Field Detail

LOG

static final org.slf4j.Logger LOG

Method Detail

evaluate

default <T> EvalContext.Value<T> evaluate(Task<T> task)

The entry point for evaluating a EvalContext.Value from a Task.

All upstreams to the task will also be evaluated through this same method.

The implementation should define how and where evaluation happens.

This method is a good place to define how for instance value memoization happens.

Type Parameters:

T - The type of the task result

Parameters:

task - The task to evaluate

Returns:

A value of the task result

evaluateInternal

default <T> EvalContext.Value<T> evaluateInternal(Task<T> task,
                                                  EvalContext context)

A variant of evaluate(Task) that allows the caller to specify the EvalContext that should be used within the graph during evaluation.

This is intended to be called from EvalContext implementations that form a composition of other contexts.

Type Parameters:

T - The type of the task result

Parameters:

task - The task to evaluate

context - The context to use in further evaluation

Returns:

A value of the task result

invokeProcessFn

default <T> EvalContext.Value<T> invokeProcessFn(TaskId taskId,
                                                 Fn<T> processFn)

Invoke the process function of a task.

This method will be called when the process function of a task is ready to be invoked. This gives this EvalContext the responsibility of invoking user code. By overriding this method, one can intercept the evaluation flow just at the moment between inputs being ready and when the user supplied function for task processing is being invoked.

The default implementation will simply invoke the function immediately inside a EvalContext.Value created by value(Fn).

Type Parameters:

T - The task value type

Parameters:

taskId - The id of the task being invoked

processFn - A lazily evaluated handle to the process function

Returns:

The (deferred) value of the process function invocation

currentTask

default Optional<Task<?>> currentTask()

When called during the evaluation of a task, this method will return the Task currently being processed. Otherwise an empty value will be returned.

The return value of this method is stable for each instance of EvalContext that is passed into the process functions. Calls from multiple threads will see the same result as longs as the calls are made to the same instance.

Returns:

The task that is being evaluated or empty if called from outside of a process function

value

<T> EvalContext.Value<T> value(Fn<T> value)

Create a EvalContext.Value with semantics defined by this EvalContext

Type Parameters:

T - The type of the value

Parameters:

value - A value value supplier

Returns:

A value with added semantics

immediateValue

default <T> EvalContext.Value<T> immediateValue(T value)

Create a EvalContext.Value with semantics defined by this EvalContext

Type Parameters:

T - The type of the value

Parameters:

value - An actual value to wrap

Returns:

A value with added semantics

promise

<T> EvalContext.Promise<T> promise()

Create a promise for a value that can be fulfilled somewhere else.

Type Parameters:

T - The type of the promised value

Returns:

A promise

listener

default TaskOperator.Listener listener()

Used to report task metadata.

sync

static EvalContext sync()

Create a default, synchronous EvalContext. The values produced by this context should behave like synchronously created values.

Returns:

A new synchronous evaluation context

async

static EvalContext async(Executor executor)

Create an asynchronous EvalContext that executes all evaluation on the given Executor.

Parameters:

executor - The executor to run evaluations on

Returns:

A new asynchronous evaluation context