Create BootClassPathCachingFileManager a subclass of JavacFileManager…

… which handles caching for the boot classpaths. The class also decides if an instance can be kept for the current compilation or needs to be updated (e.g., if a bootclasspath digest has changed)

Note: BootClassPathCachingFileManager is used only with singleplex-workers that have list of boot classpaths along with their digest information.

RELNOTES: None.
PiperOrigin-RevId: 387592935

src/java_tools/buildjar/java/com/google/devtools/build/buildjar/BUILD

@@ -42,11 +42,15 @@ JAVAC_OPTIONS_SRCS = [
     "javac/WerrorCustomOption.java",
 ]
 
+JAVAC_TEST_SRCS = [
+    "javac/BootClassPathCachingFileManagerTest.java",
+]
+
 java_library(
     name = "javac",
     srcs = glob(
         ["javac/*.java"],
-        exclude = JAVAC_OPTIONS_SRCS,
+        exclude = JAVAC_OPTIONS_SRCS + JAVAC_TEST_SRCS,
     ),
     deps = [
         ":invalid_command_line_exception",
@@ -204,3 +208,16 @@ bootstrap_java_binary(
         "//src/java_tools/buildjar/java/com/google/devtools/build/buildjar/jarhelper:bootstrap_jarhelper",
     ],
 )
+
+java_test(
+    name = "BootClassPathCachingFileManagerTest",
+    srcs = ["javac/BootClassPathCachingFileManagerTest.java"],
+    deps = [
+        ":javac",
+        "//third_party:guava",
+        "//third_party:junit4",
+        "//third_party:truth",
+        "//third_party/java/jdk/langtools:javac",
+        "//third_party/protobuf:protobuf_java",
+    ],
+)

src/java_tools/buildjar/java/com/google/devtools/build/buildjar/javac/BlazeJavacMain.java

@@ -50,8 +50,11 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Optional;
+import java.util.Set;
 import javax.tools.Diagnostic;
 import javax.tools.DiagnosticListener;
+import javax.tools.JavaFileObject;
+import javax.tools.JavaFileObject.Kind;
 import javax.tools.StandardLocation;
 
 /**
@@ -109,6 +112,11 @@ public static BlazeJavacResult compile(BlazeJavacArguments arguments) {
     try (JavacFileManager fileManager =
         new ClassloaderMaskingFileManager(context, arguments.builtinProcessors())) {
 
+      bootFileManager = getBootFileManager(arguments);
+      if (bootFileManager != null) {
+        setLocations(bootFileManager, arguments);
+      }
+
       setLocations(fileManager, arguments);
 
       JavacTask task =
@@ -305,6 +313,32 @@ private static void setLocations(JavacFileManager fileManager, BlazeJavacArgumen
     }
   }
 
+  /** a javac file manager instance specific only for boot classpaths */
+  private static BootClassPathCachingFileManager bootFileManager;
+
+  /**
+   * Returns a BootClassPathCachingFileManager instance if it is a singleplex-worker with valid
+   * arguments
+   */
+  private static BootClassPathCachingFileManager getBootFileManager(BlazeJavacArguments arguments) {
+
+    if (!arguments.requestId().isPresent()) {
+      // worker mode is not enabled
+      return null;
+    }
+    if (arguments.requestId().getAsInt() != 0) {
+      // worker is not singleplex worker
+      return null;
+    }
+    if (!BootClassPathCachingFileManager.areArgumentsValid(arguments)) {
+      return null;
+    }
+
+    return (bootFileManager != null && !bootFileManager.needsUpdate(arguments))
+        ? bootFileManager
+        : new BootClassPathCachingFileManager(new Context(), arguments);
+  }
+
   /**
    * When Bazel invokes JavaBuilder, it puts javac.jar on the bootstrap class path and
    * JavaBuilder_deploy.jar on the user class path. We need Error Prone to be available on the
@@ -321,6 +355,16 @@ public ClassloaderMaskingFileManager(Context context, ImmutableSet<String> built
       this.builtinProcessors = builtinProcessors;
     }
 
+    @Override
+    public Iterable<JavaFileObject> list(
+        Location location, String packageName, Set<Kind> kinds, boolean recurse)
+        throws IOException {
+      if (bootFileManager != null && location == StandardLocation.PLATFORM_CLASS_PATH) {
+        return bootFileManager.list(location, packageName, kinds, recurse);
+      }
+      return super.list(location, packageName, kinds, recurse);
+    }
+
     @Override
     protected ClassLoader getClassLoader(URL[] urls) {
       return new URLClassLoader(

src/java_tools/buildjar/java/com/google/devtools/build/buildjar/javac/BootClassPathCachingFileManager.java

@@ -0,0 +1,85 @@
+// Copyright 2021 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.buildjar.javac;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.protobuf.ByteString;
+import com.sun.tools.javac.file.JavacFileManager;
+import com.sun.tools.javac.util.Context;
+import java.nio.file.Path;
+import java.util.HashMap;
+import java.util.Map;
+
+/** A subclass of the JavacFileManager that handles only boot classpaths */
+@VisibleForTesting
+class BootClassPathCachingFileManager extends JavacFileManager {
+
+  private final Map<String, ByteString> bootJarsAndDigest = new HashMap<>();
+
+  /** Create a JavacFileManager using a given context and BlazeJavacArguments */
+  public BootClassPathCachingFileManager(Context context, BlazeJavacArguments arguments) {
+    super(context, false, UTF_8);
+
+    for (Path bootClassPath : arguments.bootClassPath()) {
+      bootJarsAndDigest.put(
+          bootClassPath.toString(), arguments.inputsAndDigest().get(bootClassPath.toString()));
+    }
+  }
+
+  /**
+   * Checks if this instance or a new instance is needed for the {@code BlazeJavacArguments}. An
+   * update is needed if the bootclasspath in {@code BlazeJavacArguments} have changed its digest.
+   */
+  @VisibleForTesting
+  boolean needsUpdate(BlazeJavacArguments arguments) {
+    for (Path bootClassPath : arguments.bootClassPath()) {
+      ByteString currDigest = arguments.inputsAndDigest().get(bootClassPath.toString());
+
+      if (currDigest == null) {
+        return true;
+      }
+
+      ByteString oldDigest = bootJarsAndDigest.putIfAbsent(bootClassPath.toString(), currDigest);
+
+      if (oldDigest != null && !oldDigest.equals(currDigest)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Checks if the bootClassPaths in {@code BlazeJavacArguments} can benefit from the {@code
+   * BootCachingFileManager}. Arguments are not valid if missing boot classpath or at least one
+   * digest
+   */
+  @VisibleForTesting
+  static boolean areArgumentsValid(BlazeJavacArguments arguments) {
+    if (arguments.bootClassPath().isEmpty()) {
+      return false;
+    }
+
+    for (Path bootClassPath : arguments.bootClassPath()) {
+      ByteString currDigest = arguments.inputsAndDigest().get(bootClassPath.toString());
+      if (currDigest == null) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+}

src/java_tools/buildjar/java/com/google/devtools/build/buildjar/javac/BootClassPathCachingFileManagerTest.java

@@ -0,0 +1,168 @@
+// Copyright 2021 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.buildjar.javac;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import com.google.protobuf.ByteString;
+import com.sun.tools.javac.util.Context;
+import java.io.IOException;
+import java.nio.file.Path;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** {@link BootClassPathCachingFileManager}Test */
+@RunWith(JUnit4.class)
+public class BootClassPathCachingFileManagerTest {
+  private ImmutableList<Path> bootClassPathsCandidates;
+  private BootClassPathCachingFileManager bootFileManager;
+
+  @Rule public final TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+  @Before
+  public void createBootFileManager() throws IOException {
+    bootClassPathsCandidates =
+        ImmutableList.of(
+            temporaryFolder.newFolder().toPath().resolve("BootClassPath0.jar"),
+            temporaryFolder.newFolder().toPath().resolve("BootClassPath1.jar"),
+            temporaryFolder.newFolder().toPath().resolve("BootClassPath2.jar"));
+
+    ImmutableList<Path> bootClassPaths =
+        ImmutableList.of(bootClassPathsCandidates.get(0), bootClassPathsCandidates.get(1));
+
+    ImmutableMap<String, ByteString> inputsAndDigest =
+        ImmutableMap.<String, ByteString>builder()
+            .put(
+                bootClassPaths.get(0).toString(),
+                ByteString.copyFromUtf8(bootClassPaths.get(0).toString()))
+            .put(
+                bootClassPaths.get(1).toString(),
+                ByteString.copyFromUtf8(bootClassPaths.get(1).toString()))
+            .build();
+
+    BlazeJavacArguments arguments =
+        BlazeJavacArguments.builder()
+            .bootClassPath(bootClassPaths)
+            .inputsAndDigest(inputsAndDigest)
+            .classOutput(temporaryFolder.newFolder().toPath().resolve("output_0.jar"))
+            .build();
+
+    bootFileManager = new BootClassPathCachingFileManager(new Context(), arguments);
+  }
+
+  @Test
+  public void testNeedsUpdate() throws IOException {
+    ImmutableList<Path> bootClassPaths =
+        ImmutableList.of(
+            bootClassPathsCandidates.get(0),
+            bootClassPathsCandidates.get(1),
+            bootClassPathsCandidates.get(2));
+
+    ImmutableMap<String, ByteString> inputsAndDigest =
+        ImmutableMap.<String, ByteString>builder()
+            .put(
+                bootClassPaths.get(0).toString(),
+                ByteString.copyFromUtf8(bootClassPaths.get(0).toString()))
+            .put(
+                bootClassPaths.get(1).toString(),
+                ByteString.copyFromUtf8(bootClassPaths.get(1).toString()))
+            .put(
+                bootClassPaths.get(2).toString(),
+                ByteString.copyFromUtf8(bootClassPaths.get(2).toString()))
+            .build();
+
+    BlazeJavacArguments arguments =
+        BlazeJavacArguments.builder()
+            .bootClassPath(bootClassPaths)
+            .inputsAndDigest(inputsAndDigest)
+            .classOutput(temporaryFolder.newFolder().toPath().resolve("output_1.jar"))
+            .build();
+
+    assertThat(bootFileManager.needsUpdate(arguments)).isFalse();
+  }
+
+  @Test
+  public void testNeedsUpdate_withDifferentDigest() throws IOException {
+    ImmutableList<Path> bootClassPaths =
+        ImmutableList.of(bootClassPathsCandidates.get(0), bootClassPathsCandidates.get(1));
+
+    ImmutableMap<String, ByteString> inputsAndDigest =
+        ImmutableMap.<String, ByteString>builder()
+            .put(bootClassPaths.get(0).toString(), ByteString.copyFromUtf8("different digest"))
+            .put(
+                bootClassPaths.get(1).toString(),
+                ByteString.copyFromUtf8(bootClassPaths.get(1).toString()))
+            .build();
+
+    BlazeJavacArguments arguments =
+        BlazeJavacArguments.builder()
+            .bootClassPath(bootClassPaths)
+            .inputsAndDigest(inputsAndDigest)
+            .classOutput(temporaryFolder.newFolder().toPath().resolve("output_1.jar"))
+            .build();
+
+    assertThat(bootFileManager.needsUpdate(arguments)).isTrue();
+  }
+
+  @Test
+  public void testAreArgumentsValid_withOneMissingDigest() throws IOException {
+    ImmutableList<Path> bootClassPaths =
+        ImmutableList.of(bootClassPathsCandidates.get(0), bootClassPathsCandidates.get(1));
+
+    ImmutableMap<String, ByteString> inputsAndDigest =
+        ImmutableMap.of(
+            bootClassPaths.get(1).toString(),
+            ByteString.copyFromUtf8(bootClassPaths.get(1).toString()));
+
+    BlazeJavacArguments arguments =
+        BlazeJavacArguments.builder()
+            .bootClassPath(bootClassPaths)
+            .inputsAndDigest(inputsAndDigest)
+            .classOutput(temporaryFolder.newFolder().toPath().resolve("output_1.jar"))
+            .build();
+
+    assertThat(BootClassPathCachingFileManager.areArgumentsValid(arguments)).isFalse();
+  }
+
+  @Test
+  public void testAreArgumentsValid_withEmptyInputsAndDigest() throws IOException {
+    ImmutableList<Path> bootClassPaths =
+        ImmutableList.of(bootClassPathsCandidates.get(0), bootClassPathsCandidates.get(1));
+
+    BlazeJavacArguments arguments =
+        BlazeJavacArguments.builder()
+            .bootClassPath(bootClassPaths)
+            .classOutput(temporaryFolder.newFolder().toPath().resolve("output_1.jar"))
+            .build();
+
+    assertThat(BootClassPathCachingFileManager.areArgumentsValid(arguments)).isFalse();
+  }
+
+  @Test
+  public void testAreArgumentsValid_withEmptyBootClassPaths() throws IOException {
+    assertThat(
+            BootClassPathCachingFileManager.areArgumentsValid(
+                BlazeJavacArguments.builder()
+                    .classOutput(temporaryFolder.newFolder().toPath().resolve("output_1.jar"))
+                    .build()))
+        .isFalse();
+  }
+}