From 15d15cf079f8dc6fc810ed0fec7cd9a0d446b316 Mon Sep 17 00:00:00 2001
From: zachh <zachh@google.com>
Date: Mon, 8 Jan 2018 11:58:07 -0800
Subject: Automated rollback of changelist 178323108

Test: tap
PiperOrigin-RevId: 181196939
Change-Id: I97405c5356814fe3ad02d498cfa96c210921c477
---
 .../common/concurrent/DialerFutureSerializer.java  | 73 +++++++++++++++++++---
 1 file changed, 66 insertions(+), 7 deletions(-)

(limited to 'java/com')

diff --git a/java/com/android/dialer/common/concurrent/DialerFutureSerializer.java b/java/com/android/dialer/common/concurrent/DialerFutureSerializer.java
index de37a2915..2629abbbe 100644
--- a/java/com/android/dialer/common/concurrent/DialerFutureSerializer.java
+++ b/java/com/android/dialer/common/concurrent/DialerFutureSerializer.java
@@ -16,24 +16,83 @@
 
 package com.android.dialer.common.concurrent;
 
+import static com.google.common.util.concurrent.Futures.immediateCancelledFuture;
+import static com.google.common.util.concurrent.Futures.immediateFuture;
+import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
+
 import com.google.common.util.concurrent.AsyncCallable;
+import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.SettableFuture;
+import java.util.concurrent.Callable;
 import java.util.concurrent.Executor;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * Serializes execution of a set of operations. This class guarantees that a submitted callable will
  * not be called before previously submitted callables have completed.
  */
 public final class DialerFutureSerializer {
+  /** This reference acts as a pointer tracking the head of a linked list of ListenableFutures. */
+  private final AtomicReference<ListenableFuture<?>> ref =
+      new AtomicReference<>(immediateFuture(null));
 
   /** Enqueues a task to run when the previous task (if any) completes. */
+  public <T> ListenableFuture<T> submit(final Callable<T> callable, Executor executor) {
+    return submitAsync(() -> immediateFuture(callable.call()), executor);
+  }
+
+  /**
+   * Enqueues a task to run when the previous task (if any) completes.
+   *
+   * <p>Cancellation does not propagate from the output future to the future returned from {@code
+   * callable}, but if the output future is cancelled before {@link AsyncCallable#call()} is
+   * invoked, {@link AsyncCallable#call()} will not be invoked.
+   */
   public <T> ListenableFuture<T> submitAsync(final AsyncCallable<T> callable, Executor executor) {
-    // TODO(zachh): This is just a dummy implementation until we fix guava API level issues.
-    try {
-      return callable.call();
-    } catch (Exception e) {
-      e.printStackTrace();
-    }
-    return null;
+    AtomicBoolean wasCancelled = new AtomicBoolean(false);
+    final AsyncCallable<T> task =
+        () -> {
+          if (wasCancelled.get()) {
+            return immediateCancelledFuture();
+          }
+          return callable.call();
+        };
+    /*
+     * Three futures are at play here:
+     * taskFuture is the future that comes from the callable.
+     * newFuture is the future we use to track the serialization of our task.
+     * oldFuture is the previous task's newFuture.
+     *
+     * newFuture is guaranteed to only complete once all tasks previously submitted to this instance
+     * once the futures returned from those submissions have completed.
+     */
+    final SettableFuture<Object> newFuture = SettableFuture.create();
+
+    final ListenableFuture<?> oldFuture = ref.getAndSet(newFuture);
+
+    // Invoke our task once the previous future completes.
+    final ListenableFuture<T> taskFuture =
+        Futures.nonCancellationPropagating(
+            Futures.submitAsync(task, runnable -> oldFuture.addListener(runnable, executor)));
+    // newFuture's lifetime is determined by taskFuture, unless taskFuture is cancelled, in which
+    // case it falls back to oldFuture's. This is to ensure that if the future we return is
+    // cancelled, we don't begin execution of the next task until after oldFuture completes.
+    taskFuture.addListener(
+        () -> {
+          if (taskFuture.isCancelled()) {
+            // Since the value of oldFuture can only ever be immediateFuture(null) or setFuture of a
+            // future that eventually came from immediateFuture(null), this doesn't leak throwables
+            // or completion values.
+            wasCancelled.set(true);
+            newFuture.setFuture(oldFuture);
+          } else {
+            newFuture.set(null);
+          }
+        },
+        directExecutor());
+
+    return taskFuture;
   }
 }
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