Reimplement blaze query using an async evaluation model. Use a concurrent backend for SkyQueryEnvironment's implementation in order to achieve parallelism.

Advantages:
-New design has no flaws that the old design had.
-Code is structured so that deadlocks due to thread starvation are impossible (yup!).

Disadvantages:
-The meat of this change needs to all be in a single CL because every single QueryFunction and QueryExpression needs to be rewritten in the async style.

Still TODO:
-Fully embrace the async model in all QueryFunctions (e.g. 'rdeps', 'allpaths').
-Use concurrency in BlazeQueryEnvironment to achieve parallel evaluation for (non SkyQuery) 'blaze query' and genquery.

--
PiperOrigin-RevId: 148690279
MOS_MIGRATED_REVID=148690279

1 files changed, 25 insertions, 26 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/query2/engine/VisibleFunction.java b/src/main/java/com/google/devtools/build/lib/query2/engine/VisibleFunction.java
index 532f331378..b09910c715 100644
--- a/src/main/java/com/google/devtools/build/lib/query2/engine/VisibleFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/query2/engine/VisibleFunction.java
@@ -14,13 +14,14 @@
 
 package com.google.devtools.build.lib.query2.engine;
 
+import com.google.common.base.Function;
 import com.google.common.collect.ImmutableList;
 import com.google.devtools.build.lib.query2.engine.QueryEnvironment.Argument;
 import com.google.devtools.build.lib.query2.engine.QueryEnvironment.ArgumentType;
 import com.google.devtools.build.lib.query2.engine.QueryEnvironment.QueryFunction;
+import com.google.devtools.build.lib.query2.engine.QueryEnvironment.QueryTaskFuture;
 import java.util.List;
 import java.util.Set;
-import java.util.concurrent.ForkJoinPool;
 
 /**
  * A visible(x, y) query expression, which computes the subset of nodes in y
@@ -52,34 +53,32 @@ public class VisibleFunction implements QueryFunction {
   }
 
   @Override
-  public <T> void eval(
+  public <T> QueryTaskFuture<Void> eval(
       final QueryEnvironment<T> env,
-      VariableContext<T> context,
+      final VariableContext<T> context,
       QueryExpression expression,
-      List<Argument> args,
-      final Callback<T> callback) throws QueryException, InterruptedException {
-    final Set<T> toSet = QueryUtil.evalAll(env, context, args.get(0).getExpression());
-    env.eval(args.get(1).getExpression(), context, new Callback<T>() {
-      @Override
-      public void process(Iterable<T> partialResult) throws QueryException, InterruptedException {
-        for (T t : partialResult) {
-          if (visibleToAll(env, toSet, t)) {
-            callback.process(ImmutableList.of(t));
+      final List<Argument> args,
+      final Callback<T> callback) {
+    final QueryTaskFuture<Set<T>> toSetFuture =
+        QueryUtil.evalAll(env, context, args.get(0).getExpression());
+    Function<Set<T>, QueryTaskFuture<Void>> computeVisibleNodesAsyncFunction =
+        new Function<Set<T>, QueryTaskFuture<Void>>() {
+          @Override
+          public QueryTaskFuture<Void> apply(final Set<T> toSet) {
+            return env.eval(args.get(1).getExpression(), context, new Callback<T>() {
+              @Override
+              public void process(Iterable<T> partialResult)
+                  throws QueryException, InterruptedException {
+                for (T t : partialResult) {
+                  if (visibleToAll(env, toSet, t)) {
+                    callback.process(ImmutableList.of(t));
+                  }
+                }
+              }
+            });
           }
-        }
-      }
-    });
-  }
-
-  @Override
-  public <T> void parEval(
-      QueryEnvironment<T> env,
-      VariableContext<T> context,
-      QueryExpression expression,
-      List<Argument> args,
-      ThreadSafeCallback<T> callback,
-      ForkJoinPool forkJoinPool) throws QueryException, InterruptedException {
-    eval(env, context, expression, args, callback);
+        };
+    return env.transformAsync(toSetFuture, computeVisibleNodesAsyncFunction);
   }
 
   /** Returns true if {@code target} is visible to all targets in {@code toSet}. */