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// 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.lib.actions;
import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import javax.annotation.Nullable;
/**
* An interface for an {@link Action}, containing only side-effect-free query methods for
* information needed during both action analysis and execution.
*
* <p>The split between {@link Action} and {@link ActionExecutionMetadata} is somewhat arbitrary,
* other than that all methods with side effects must belong to the former.
*/
public interface ActionExecutionMetadata extends ActionAnalysisMetadata {
/**
* Return this key to signify a failed key computation.
*
* <p>Actions that return this value should fail to execute.
*
* <p>Consumers must either gracefully handle multiple failed actions having the same key,
* (recommended), or check against this value explicitly.
*/
String KEY_ERROR = "1ea50e01-0349-4552-80cf-76cf520e8592";
/**
* If this executable can supply verbose information, returns a string that can be used as a
* progress message while this executable is running. A return value of {@code null} indicates no
* message should be reported.
*/
@Nullable
String getProgressMessage();
/**
* Returns a string encoding all of the significant behaviour of this Action that might affect the
* output. The general contract of <code>getKey</code> is this: if the work to be performed by the
* execution of this action changes, the key must change.
*
* <p>As a corollary, the build system is free to omit the execution of an Action <code>a1</code>
* if (a) at some time in the past, it has already executed an Action <code>a0</code> with the
* same key as <code>a1</code>, (b) the names and contents of the input files listed by <code>
* a1.getInputs()</code> are identical to the names and contents of the files listed by <code>
* a0.getInputs()</code>, and (c) the names and values in the client environment of the variables
* listed by <code>a1.getClientEnvironmentVariables()</code> are identical to those listed by
* <code>a0.getClientEnvironmentVariables()</code>.
*
* <p>Examples of changes that should affect the key are:
*
* <ul>
* <li>Changes to the BUILD file that materially affect the rule which gave rise to this Action.
* <li>Changes to the command-line options, environment, or other global configuration resources
* which affect the behaviour of this kind of Action (other than changes to the names of the
* input/output files, which are handled externally).
* <li>An upgrade to the build tools which changes the program logic of this kind of Action
* (typically this is achieved by incorporating a UUID into the key, which is changed each
* time the program logic of this action changes).
* </ul>
*/
String getKey();
/**
* Returns a human-readable description of the inputs to {@link #getKey()}.
* Used in the output from '--explain', and in error messages for
* '--check_up_to_date' and '--check_tests_up_to_date'.
* May return null, meaning no extra information is available.
*
* <p>If the return value is non-null, for consistency it should be a multiline message of the
* form:
* <pre>
* <var>Summary</var>
* <var>Fieldname</var>: <var>value</var>
* <var>Fieldname</var>: <var>value</var>
* ...
* </pre>
* where each line after the first one is intended two spaces, and where any fields that might
* contain newlines or other funny characters are escaped using {@link
* com.google.devtools.build.lib.shell.ShellUtils#shellEscape}.
* For example:
* <pre>
* Compiling foo.cc
* Command: /usr/bin/gcc
* Argument: '-c'
* Argument: foo.cc
* Argument: '-o'
* Argument: foo.o
* </pre>
*/
@Nullable String describeKey();
/**
* Get the {@link RunfilesSupplier} providing runfiles needed by this action.
*/
RunfilesSupplier getRunfilesSupplier();
/**
* Returns true iff the getInputs set is known to be complete.
*
* <p>For most Actions, this always returns true, but in some cases (e.g. C++ compilation), inputs
* are dynamically discovered from the previous execution of the Action, and so before the initial
* execution, this method will return false in those cases.
*
* <p>Any builder <em>must</em> unconditionally execute an Action for which inputsKnown() returns
* false, regardless of all other inferences made by its dependency analysis. In addition, all
* prerequisites mentioned in the (possibly incomplete) value returned by getInputs must also be
* built first, as usual.
*/
@ThreadSafe
boolean inputsDiscovered();
/**
* Returns true iff inputsKnown() may ever return false.
*/
@ThreadSafe
boolean discoversInputs();
}
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