src/main/java/com/google/devtools/build/skyframe/SkyFunction.java - bazel - Git at Google

 // 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
      * &lt;potentialMatchesRef, matchCriterion&gt;. 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();
   }
 }
	// 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();
	}
	}