// Copyright 2014 The Bazel Authors. All rights reserved.
//
// 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 com.google.devtools.build.skyframe;
import com.google.common.annotations.VisibleForTesting;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import com.google.devtools.build.lib.events.ExtendedEventHandler;
import java.util.Map;
import javax.annotation.Nullable;
/**
* Machinery to evaluate a single value.
*
* <p>The SkyFunction {@link #compute} implementation is supposed to access only direct
* dependencies of the value. However, the direct dependencies need not be known in advance. The
* implementation can request arbitrary values using {@link Environment#getValue}. If the values
* are not ready, the call will return {@code null}; in that case the implementation should just
* return {@code null}, in which case the missing dependencies will be computed and the {@link
* #compute} method will be started again.
* */
public interface SkyFunction {
/**
* When a value is requested, this method is called with the name of the value and a
* dependency-tracking environment.
*
* <p>This method should return a non-{@code null} value, or {@code null} if any dependencies
* were missing ({@link Environment#valuesMissing} was true before returning). In that case the
* missing dependencies will be computed and the {@code compute} method called again.
*
* <p>This method should throw if it fails, or if one of its dependencies fails with an
* exception and this method cannot recover. If one of its dependencies fails and this method can
* enrich the exception with additional context, then this method should catch that exception and
* throw another containing that additional context. If it has no such additional context, then
* it should allow its dependency's exception to be thrown through it.
*
* @throws SkyFunctionException on failure
* @throws InterruptedException if interrupted
*/
@ThreadSafe
@Nullable
SkyValue compute(SkyKey skyKey, Environment env)
throws SkyFunctionException, InterruptedException;
/**
* Extracts a tag (target label) from a SkyKey if it has one. Otherwise return {@code null}.
*
* <p>The tag is used for filtering out non-error event messages that do not match
* --output_filter flag. If a SkyFunction returns {@code null} in this method it means that all
* the info/warning messages associated with this value will be shown, no matter what
* --output_filter says.
*/
@Nullable
String extractTag(SkyKey skyKey);
/**
* The services provided to the {@link SkyFunction#compute} implementation by the Skyframe
* evaluation framework.
*/
interface Environment {
/**
* Returns a direct dependency. If the specified value is not in the set of already evaluated
* direct dependencies, returns {@code null}. Also returns {@code null} if the specified value
* has already been evaluated and found to be in error.
*
* <p>On a subsequent evaluation, if any of this value's dependencies have changed they will be
* re-evaluated in the same order as originally requested by the {@code SkyFunction} using this
* {@code getValue} call (see {@link #getValues} for when preserving the order is not
* important).
*
* <p>This method and the ones below may throw {@link InterruptedException}. Such exceptions
* must not be caught by the {@link SkyFunction#compute} implementation. Instead, they should be
* propagated up to the caller of {@link SkyFunction#compute}.
*/
@Nullable
SkyValue getValue(SkyKey valueName) throws InterruptedException;
/**
* Returns a direct dependency. If the specified value is not in the set of already evaluated
* direct dependencies, returns {@code null}. If the specified value has already been evaluated
* and found to be in error, throws the exception coming from the error, so long as the
* exception is of one of the specified types. SkyFunction implementations may use this method
* to continue evaluation even if one of their dependencies is in error by catching the thrown
* exception and proceeding. The caller must specify the exception type(s) that might be thrown
* using the {@code exceptionClass} argument(s). If the dependency's exception is not an
* instance of {@code exceptionClass}, {@code null} is returned.
*
* <p>The exception class given cannot be a supertype or a subtype of {@link RuntimeException},
* or a subtype of {@link InterruptedException}. See {@link
* SkyFunctionException#validateExceptionType} for details.
*/
@Nullable
<E extends Exception> SkyValue getValueOrThrow(SkyKey depKey, Class<E> exceptionClass)
throws E, InterruptedException;
@Nullable
<E1 extends Exception, E2 extends Exception> SkyValue getValueOrThrow(
SkyKey depKey, Class<E1> exceptionClass1, Class<E2> exceptionClass2)
throws E1, E2, InterruptedException;
@Nullable
<E1 extends Exception, E2 extends Exception, E3 extends Exception> SkyValue getValueOrThrow(
SkyKey depKey,
Class<E1> exceptionClass1,
Class<E2> exceptionClass2,
Class<E3> exceptionClass3)
throws E1, E2, E3, InterruptedException;
@Nullable
<E1 extends Exception, E2 extends Exception, E3 extends Exception, E4 extends Exception>
SkyValue getValueOrThrow(
SkyKey depKey,
Class<E1> exceptionClass1,
Class<E2> exceptionClass2,
Class<E3> exceptionClass3,
Class<E4> exceptionClass4)
throws E1, E2, E3, E4, InterruptedException;
@Nullable
<
E1 extends Exception,
E2 extends Exception,
E3 extends Exception,
E4 extends Exception,
E5 extends Exception>
SkyValue getValueOrThrow(
SkyKey depKey,
Class<E1> exceptionClass1,
Class<E2> exceptionClass2,
Class<E3> exceptionClass3,
Class<E4> exceptionClass4,
Class<E5> exceptionClass5)
throws E1, E2, E3, E4, E5, InterruptedException;
/**
* Requests {@code depKeys} "in parallel", independent of each others' values. These keys may be
* thought of as a "dependency group" -- they are requested together by this value.
*
* <p>In general, if the result of one getValue call can affect the argument of a later getValue
* call, the two calls cannot be merged into a single getValues call, since the result of the
* first call might change on a later evaluation. Inversely, if the result of one getValue call
* cannot affect the parameters of the next getValue call, the two keys can form a dependency
* group and the two getValue calls merged into one getValues call.
*
* <p>This means that on subsequent evaluations, when checking to see if dependencies require
* re-evaluation, all the values in this group may be simultaneously checked. A SkyFunction
* should request a dependency group if checking the deps serially on a subsequent evaluation
* would take too long, and if the {@link #compute} method would request all deps anyway as long
* as no earlier deps had changed. SkyFunction.Environment implementations may also choose to
* request these deps in parallel on the first evaluation, potentially speeding it up.
*
* <p>While re-evaluating every value in the group may take longer than re-evaluating just the
* first one and finding that it has changed, no extra work is done: the contract of the
* dependency group means that the {@link #compute} method, when called to re-evaluate this
* value, will request all values in the group again anyway, so they would have to have been
* built in any case.
*
* <p>Example of when to use getValues: A ListProcessor value is built with key inputListRef.
* The {@link #compute} method first calls getValue(InputList.key(inputListRef)), and retrieves
* inputList. It then iterates through inputList, calling getValue on each input. Finally, it
* processes the whole list and returns. Say inputList is (a, b, c). Since the {@link #compute}
* method will unconditionally call getValue(a), getValue(b), and getValue (c), the {@link
* #compute} method can instead just call getValues({a, b, c}). If the value is later dirtied
* the evaluator will evaluate a, b, and c in parallel (assuming the inputList value was
* unchanged), and re-evaluate the ListProcessor value only if at least one of them was changed.
* On the other hand, if the InputList changes to be (a, b, d), then the evaluator will see that
* the first dep has changed, and call the {@link #compute} method to re-evaluate from scratch,
* without considering the dep group of {a, b, c}.
*
* <p>Example of when not to use getValues: A BestMatch value is built with key
* <potentialMatchesRef, matchCriterion>. The {@link #compute} method first calls
* getValue(PotentialMatches.key(potentialMatchesRef) and retrieves potentialMatches. It then
* iterates through potentialMatches, calling getValue on each potential match until it finds
* one that satisfies matchCriterion. In this case, if potentialMatches is (a, b, c), it would
* be <i>incorrect</i> to call getValues({a, b, c}), because it is not known yet whether
* requesting b or c will be necessary -- if a matches, then we will never call b or c.
*
* <p>Returns a map, {@code m}. For all {@code k} in {@code depKeys}, {@code m.containsKey(k)}
* is {@code true}, and, {@code m.get(k) != null} iff the dependency was already evaluated and
* was not in error.
*/
Map<SkyKey, SkyValue> getValues(Iterable<SkyKey> depKeys) throws InterruptedException;
/**
* Similar to {@link #getValues} but allows the caller to specify a set of types that are proper
* subtypes of Exception (see {@link SkyFunctionException} for more details) to find out whether
* any of the dependencies' evaluations resulted in exceptions of those types. The returned
* objects may throw when attempting to retrieve their value.
*
* <p>Callers should prioritize their responsibility to detect and handle errors in the returned
* map over their responsibility to return {@code null} if values are missing. This is because
* in nokeep_going evaluations, an error from a low level dependency is given a chance to be
* enriched by its reverse-dependencies, if possible.
*
* <p>Returns a map, {@code m}. For all {@code k} in {@code depKeys}, {@code m.get(k) != null}.
* For all {@code v} such that there is some {@code k} such that {@code m.get(k) == v}, the
* following is true: {@code v.get() != null} iff the dependency {@code k} was already evaluated
* and was not in error. {@code v.get()} throws {@code E} iff the dependency {@code k} was
* already evaluated with an error in the specified set of {@link Exception} types.
*/
<E extends Exception> Map<SkyKey, ValueOrException<E>> getValuesOrThrow(
Iterable<SkyKey> depKeys, Class<E> exceptionClass) throws InterruptedException;
<E1 extends Exception, E2 extends Exception>
Map<SkyKey, ValueOrException2<E1, E2>> getValuesOrThrow(
Iterable<SkyKey> depKeys, Class<E1> exceptionClass1, Class<E2> exceptionClass2)
throws InterruptedException;
<E1 extends Exception, E2 extends Exception, E3 extends Exception>
Map<SkyKey, ValueOrException3<E1, E2, E3>> getValuesOrThrow(
Iterable<SkyKey> depKeys,
Class<E1> exceptionClass1,
Class<E2> exceptionClass2,
Class<E3> exceptionClass3)
throws InterruptedException;
<E1 extends Exception, E2 extends Exception, E3 extends Exception, E4 extends Exception>
Map<SkyKey, ValueOrException4<E1, E2, E3, E4>> getValuesOrThrow(
Iterable<SkyKey> depKeys,
Class<E1> exceptionClass1,
Class<E2> exceptionClass2,
Class<E3> exceptionClass3,
Class<E4> exceptionClass4)
throws InterruptedException;
<
E1 extends Exception,
E2 extends Exception,
E3 extends Exception,
E4 extends Exception,
E5 extends Exception>
Map<SkyKey, ValueOrException5<E1, E2, E3, E4, E5>> getValuesOrThrow(
Iterable<SkyKey> depKeys,
Class<E1> exceptionClass1,
Class<E2> exceptionClass2,
Class<E3> exceptionClass3,
Class<E4> exceptionClass4,
Class<E5> exceptionClass5)
throws InterruptedException;
/**
* Returns whether there was a previous getValue[s][OrThrow] that indicated a missing
* dependency. Formally, returns true iff at least one of the following occurred:
*
* <ul>
* <li>getValue[OrThrow](k[, c]) returned {@code null} for some k</li>
* <li>getValues(ks).get(k) == {@code null} for some ks and k such that ks.contains(k)</li>
* <li>
* getValuesOrThrow(ks, c).get(k).get() == {@code null} for some ks and k such that
* ks.contains(k)
* </li>
* </ul>
*
* <p>If this returns true, the {@link SkyFunction} must return {@code null}.
*/
boolean valuesMissing();
/**
* Returns the {@link EventHandler} that a SkyFunction should use to print any errors, warnings,
* or progress messages during execution of {@link SkyFunction#compute}.
*/
ExtendedEventHandler getListener();
/** Returns whether we are currently in error bubbling. */
@VisibleForTesting
boolean inErrorBubblingForTesting();
}
}