diff --git a/src/future/Future.php b/src/future/Future.php
index f58a5287..f69f14bc 100644
--- a/src/future/Future.php
+++ b/src/future/Future.php
@@ -1,157 +1,211 @@
 <?php
 
 /**
  * A 'future' or 'promise' is an object which represents the result of some
  * pending computation. For a more complete overview of futures, see
  * @{article:Using Futures}.
  */
 abstract class Future extends Phobject {
 
   private $hasResult = false;
+  private $hasStarted = false;
+  private $hasEnded = false;
   private $result;
   private $exception;
+  private $futureKey;
 
   /**
    * Is this future's process complete? Specifically, can this future be
    * resolved without blocking?
    *
    * @return bool  If true, the external process is complete and resolving this
    *               future will not block.
    */
   abstract public function isReady();
 
   /**
    * Resolve a future and return its result, blocking until the result is ready
    * if necessary.
    *
    * @return wild Future result.
    */
   public function resolve() {
     $args = func_get_args();
     if (count($args)) {
       throw new Exception(
         pht(
           'Parameter "timeout" to "Future->resolve()" is no longer '.
           'supported. Update the caller so it no longer passes a '.
           'timeout.'));
     }
 
+    if ($this->hasException()) {
+      throw $this->getException();
+    }
+
     if (!$this->hasResult()) {
       $graph = new FutureIterator(array($this));
       $graph->resolveAll();
     }
 
-    if ($this->hasException()) {
-      throw $this->getException();
+    return $this->getResult();
+  }
+
+  final public function startFuture() {
+    if ($this->hasStarted) {
+      throw new Exception(
+        pht(
+          'Future has already started; futures can not start more '.
+          'than once.'));
     }
+    $this->hasStarted = true;
 
-    return $this->getResult();
+    $this->isReady();
   }
 
   final public function updateFuture() {
     if ($this->hasException()) {
       return;
     }
 
     if ($this->hasResult()) {
       return;
     }
 
     try {
       $this->isReady();
     } catch (Exception $ex) {
       $this->setException($ex);
     } catch (Throwable $ex) {
       $this->setException($ex);
     }
   }
 
+  final public function endFuture() {
+    if (!$this->hasException() && !$this->hasResult()) {
+      throw new Exception(
+        pht(
+          'Trying to end a future which has no exception and no result. '.
+          'Futures must resolve before they can be ended.'));
+    }
+
+    if ($this->hasEnded) {
+      throw new Exception(
+        pht(
+          'Future has already ended; futures can not end more '.
+          'than once.'));
+    }
+    $this->hasEnded = true;
+  }
+
   /**
    * Retrieve a list of sockets which we can wait to become readable while
    * a future is resolving. If your future has sockets which can be
    * `select()`ed, return them here (or in @{method:getWriteSockets}) to make
-   * the resolve loop  do a `select()`. If you do not return sockets in either
+   * the resolve loop do a `select()`. If you do not return sockets in either
    * case, you'll get a busy wait.
    *
    * @return list  A list of sockets which we expect to become readable.
    */
   public function getReadSockets() {
     return array();
   }
 
 
   /**
    * Retrieve a list of sockets which we can wait to become writable while a
    * future is resolving. See @{method:getReadSockets}.
    *
    * @return list  A list of sockets which we expect to become writable.
    */
   public function getWriteSockets() {
     return array();
   }
 
 
   /**
    * Default amount of time to wait on stream select for this future. Normally
    * 1 second is fine, but if the future has a timeout sooner than that it
    * should return the amount of time left before the timeout.
    */
   public function getDefaultWait() {
     return 1;
   }
 
   public function start() {
     $this->isReady();
     return $this;
   }
 
   /**
    * Retrieve the final result of the future.
    *
    * @return wild Final resolution of this future.
    */
   final protected function getResult() {
     if (!$this->hasResult()) {
       throw new Exception(
         pht(
           'Future has not yet resolved. Resolve futures before retrieving '.
           'results.'));
     }
 
     return $this->result;
   }
 
   final protected function setResult($result) {
     if ($this->hasResult()) {
       throw new Exception(
         pht(
           'Future has already resolved. Futures may not resolve more than '.
           'once.'));
     }
 
     $this->hasResult = true;
     $this->result = $result;
 
     return $this;
   }
 
   final public function hasResult() {
     return $this->hasResult;
   }
 
   final private function setException($exception) {
     // NOTE: The parameter may be an Exception or a Throwable.
     $this->exception = $exception;
     return $this;
   }
 
   final private function getException() {
     return $this->exception;
   }
 
   final public function hasException() {
     return ($this->exception !== null);
   }
 
+  final public function setFutureKey($key) {
+    if ($this->futureKey !== null) {
+      throw new Exception(
+        pht(
+          'Future already has a key ("%s") assigned.',
+          $key));
+    }
+
+    $this->futureKey = $key;
+
+    return $this;
+  }
+
+  final public function getFutureKey() {
+    static $next_key = 1;
+
+    if ($this->futureKey === null) {
+      $this->futureKey = sprintf('Future/%d', $next_key++);
+    }
+
+    return $this->futureKey;
+  }
 
 }
diff --git a/src/future/FutureIterator.php b/src/future/FutureIterator.php
index c8b01294..772fdc77 100644
--- a/src/future/FutureIterator.php
+++ b/src/future/FutureIterator.php
@@ -1,382 +1,468 @@
 <?php
 
 /**
  * FutureIterator aggregates @{class:Future}s and allows you to respond to them
  * in the order they resolve. This is useful because it minimizes the amount of
  * time your program spends waiting on parallel processes.
  *
  *   $futures = array(
  *     'a.txt' => new ExecFuture('wc -c a.txt'),
  *     'b.txt' => new ExecFuture('wc -c b.txt'),
  *     'c.txt' => new ExecFuture('wc -c c.txt'),
  *   );
  *
  *   foreach (new FutureIterator($futures) as $key => $future) {
  *     // IMPORTANT: keys are preserved but the order of elements is not. This
  *     // construct iterates over the futures in the order they resolve, so the
  *     // fastest future is the one you'll get first. This allows you to start
  *     // doing followup processing as soon as possible.
  *
  *     list($err, $stdout) = $future->resolve();
  *     do_some_processing($stdout);
  *   }
  *
  * For a general overview of futures, see @{article:Using Futures}.
  *
  * @task  basics    Basics
  * @task  config    Configuring Iteration
  * @task  iterator  Iterator Interface
  * @task  internal  Internals
  */
-final class FutureIterator extends Phobject implements Iterator {
+final class FutureIterator
+  extends Phobject
+  implements Iterator {
 
-  protected $wait     = array();
-  protected $work     = array();
-  protected $futures  = array();
-  protected $key;
+  private $hold = array();
+  private $wait = array();
+  private $work = array();
 
-  protected $limit;
+  private $futures = array();
+  private $key;
 
-  protected $timeout;
-  protected $isTimeout = false;
+  private $limit;
+
+  private $timeout;
+  private $isTimeout = false;
+  private $hasRewound = false;
 
 
 /* -(  Basics  )------------------------------------------------------------- */
 
 
   /**
    * Create a new iterator over a list of futures.
    *
    * @param list  List of @{class:Future}s to resolve.
    * @task basics
    */
   public function __construct(array $futures) {
     assert_instances_of($futures, 'Future');
-    $this->futures = $futures;
+
+    $respect_keys = !phutil_is_natural_list($futures);
+
+    foreach ($futures as $map_key => $future) {
+      if ($respect_keys) {
+        $future->setFutureKey($map_key);
+      }
+      $this->addFuture($future);
+    }
   }
 
 
   /**
    * Block until all futures resolve.
    *
    * @return void
    * @task basics
    */
   public function resolveAll() {
-    iterator_to_array($this);
+    // If a caller breaks out of a "foreach" and then calls "resolveAll()",
+    // interpret it to mean that we should iterate over whatever futures
+    // remain.
+
+    if ($this->hasRewound) {
+      while ($this->valid()) {
+        $this->next();
+      }
+    } else {
+      iterator_to_array($this);
+    }
   }
 
   /**
    * Add another future to the set of futures. This is useful if you have a
    * set of futures to run mostly in parallel, but some futures depend on
    * others.
    *
    * @param Future  @{class:Future} to add to iterator
    * @task basics
    */
-  public function addFuture(Future $future, $key = null) {
-    if ($key === null) {
-      $this->futures[] = $future;
-      $this->wait[] = last_key($this->futures);
-    } else if (!isset($this->futures[$key])) {
-      $this->futures[$key] = $future;
-      $this->wait[] = $key;
-    } else {
-      throw new Exception(pht('Invalid key %s', $key));
+  public function addFuture(Future $future) {
+    $key = $future->getFutureKey();
+
+    if (isset($this->futures[$key])) {
+      throw new Exception(
+        pht(
+          'This future graph already has a future with key "%s". Each '.
+          'future must have a unique key.',
+          $key));
     }
 
-    // Start running the future if we don't have $this->limit futures running
-    // already. updateWorkingSet() won't start running the future if there's no
-    // limit, so we'll manually poke it here in that case.
-    $this->updateWorkingSet();
-    if (!$this->limit) {
-      $future->isReady();
-    }
+    $this->futures[$key] = $future;
+    $this->hold[$key] = $key;
+
     return $this;
   }
 
 
 /* -(  Configuring Iteration  )---------------------------------------------- */
 
 
   /**
    * Set a maximum amount of time you want to wait before the iterator will
    * yield a result. If no future has resolved yet, the iterator will yield
    * null for key and value. Among other potential uses, you can use this to
    * show some busy indicator:
    *
    *   $futures = id(new FutureIterator($futures))
    *     ->setUpdateInterval(1);
    *   foreach ($futures as $future) {
    *     if ($future === null) {
    *       echo "Still working...\n";
    *     } else {
    *       // ...
    *     }
    *   }
    *
    * This will echo "Still working..." once per second as long as futures are
    * resolving. By default, FutureIterator never yields null.
    *
    * @param float Maximum number of seconds to block waiting on futures before
    *              yielding null.
    * @return this
    *
    * @task config
    */
   public function setUpdateInterval($interval) {
     $this->timeout = $interval;
     return $this;
   }
 
 
   /**
    * Limit the number of simultaneously executing futures.
    *
    *  $futures = id(new FutureIterator($futures))
    *    ->limit(4);
    *  foreach ($futures as $future) {
    *    // Run no more than 4 futures simultaneously.
    *  }
    *
    * @param int Maximum number of simultaneous jobs allowed.
    * @return this
    *
    * @task config
    */
   public function limit($max) {
     $this->limit = $max;
     return $this;
   }
 
 
+  public function setMaximumWorkingSetSize($limit) {
+    $this->limit = $limit;
+    return $this;
+  }
+
+  public function getMaximumWorkingSetSize() {
+    return $this->limit;
+  }
+
 /* -(  Iterator Interface  )------------------------------------------------- */
 
 
   /**
    * @task iterator
    */
   public function rewind() {
-    $this->wait = array_keys($this->futures);
-    $this->work = null;
-    $this->updateWorkingSet();
+    if ($this->hasRewound) {
+      throw new Exception(
+        pht('Future graphs can not be rewound.'));
+    }
+    $this->hasRewound = true;
+
     $this->next();
   }
 
   /**
    * @task iterator
    */
   public function next() {
     $this->key = null;
-    if (!count($this->wait)) {
+
+    $this->updateWorkingSet();
+
+    if (!$this->work) {
       return;
     }
 
-    $read_sockets = array();
-    $write_sockets = array();
-
     $start = microtime(true);
     $timeout = $this->timeout;
     $this->isTimeout = false;
 
-    $check = $this->getWorkingSet();
+    $working_set = array_select_keys($this->futures, $this->work);
 
-    $resolve = null;
-    do {
-      $read_sockets    = array();
-      $write_sockets   = array();
-      $can_use_sockets = true;
-      $wait_time       = 1;
-      foreach ($check as $wait => $key) {
-        $future = $this->futures[$key];
+    while (true) {
+      // Update every future first. This is a no-op on futures which have
+      // already resolved or failed, but we want to give futures an
+      // opportunity to make progress even if we can resolve something.
 
+      foreach ($working_set as $future_key => $future) {
         $future->updateFuture();
+      }
+
+      // Check if any future has resolved or failed. If we have any such
+      // futures, we'll return the first one from the iterator.
 
+      $resolve_key = null;
+      foreach ($working_set as $future_key => $future) {
         if ($future->hasException()) {
-          if ($resolve === null) {
-            $resolve = $wait;
-          }
-          continue;
+          $resolve_key = $future_key;
+          break;
         }
 
         if ($future->hasResult()) {
-          if ($resolve === null) {
-            $resolve = $wait;
-          }
-          continue;
+          $resolve_key = $future_key;
+          break;
         }
+      }
 
-        $got_sockets = false;
-        $socks = $future->getReadSockets();
-        if ($socks) {
-          $got_sockets = true;
-          foreach ($socks as $socket) {
-            $read_sockets[] = $socket;
-          }
-        }
+      // We've found a future to resolve, so we're done here for now.
 
-        $socks = $future->getWriteSockets();
-        if ($socks) {
-          $got_sockets = true;
-          foreach ($socks as $socket) {
-            $write_sockets[] = $socket;
-          }
-        }
+      if ($resolve_key !== null) {
+        $this->moveFutureToDone($resolve_key);
+        return;
+      }
 
-        // If any currently active future had neither read nor write sockets,
-        // we can't wait for the current batch of items using sockets.
-        if (!$got_sockets) {
-          $can_use_sockets = false;
-        } else {
-          $wait_time = min($wait_time, $future->getDefaultWait());
+      // We don't have any futures to resolve yet. Check if we're reached
+      // an update interval.
+
+      $wait_time = 1;
+      if ($timeout !== null) {
+        $elapsed = microtime(true) - $start;
+
+        if ($elapsed > $timeout) {
+          $this->isTimeout = true;
+          return;
         }
+
+        $wait_time = min($wait_time, $timeout - $elapsed);
       }
 
-      if ($resolve === null) {
-
-        // Check for a setUpdateInterval() timeout.
-        if ($timeout !== null) {
-          $elapsed = microtime(true) - $start;
-          if ($elapsed > $timeout) {
-            $this->isTimeout = true;
-            return;
-          } else {
-            $wait_time = $timeout - $elapsed;
-          }
+      // We're going to wait. If possible, we'd like to wait with sockets.
+      // If we can't, we'll just sleep.
+
+      $read_sockets = array();
+      $write_sockets = array();
+      foreach ($working_set as $future_key => $future) {
+        $sockets = $future->getReadSockets();
+        foreach ($sockets as $socket) {
+          $read_sockets[] = $socket;
         }
 
-        if ($can_use_sockets) {
-          $this->waitForSockets($read_sockets, $write_sockets, $wait_time);
-        } else {
-          usleep(1000);
+        $sockets = $future->getWriteSockets();
+        foreach ($sockets as $socket) {
+          $write_sockets[] = $socket;
         }
       }
-    } while ($resolve === null);
-
-    $this->key = $this->wait[$resolve];
-    unset($this->wait[$resolve]);
 
-    $this->updateWorkingSet();
+      $use_sockets = ($read_sockets || $write_sockets);
+      if ($use_sockets) {
+        foreach ($working_set as $future) {
+          $wait_time = min($wait_time, $future->getDefaultWait());
+        }
+        $this->waitForSockets($read_sockets, $write_sockets, $wait_time);
+      } else {
+        usleep(1000);
+      }
+    }
   }
 
   /**
    * @task iterator
    */
   public function current() {
     if ($this->isTimeout) {
       return null;
     }
     return $this->futures[$this->key];
   }
 
   /**
    * @task iterator
    */
   public function key() {
     if ($this->isTimeout) {
       return null;
     }
     return $this->key;
   }
 
   /**
    * @task iterator
    */
   public function valid() {
     if ($this->isTimeout) {
       return true;
     }
     return ($this->key !== null);
   }
 
 
 /* -(  Internals  )---------------------------------------------------------- */
 
-
   /**
    * @task internal
    */
-  protected function getWorkingSet() {
-    if ($this->work === null) {
-      return $this->wait;
+  protected function updateWorkingSet() {
+    $limit = $this->getMaximumWorkingSetSize();
+    $work_count = count($this->work);
+
+    // If we're already working on the maximum number of futures, we just have
+    // to wait for something to resolve. There's no benefit to updating the
+    // queue since we can never make any meaningful progress.
+
+    if ($limit) {
+      if ($work_count >= $limit) {
+        return;
+      }
     }
 
-    return $this->work;
-  }
+    // If any futures that are currently held are no longer blocked by
+    // dependencies, move them from "hold" to "wait".
 
-  /**
-   * @task internal
-   */
-  protected function updateWorkingSet() {
-    if (!$this->limit) {
-      return;
+    foreach ($this->hold as $future_key) {
+      if (!$this->canMoveFutureToWait($future_key)) {
+        continue;
+      }
+
+      $this->moveFutureToWait($future_key);
+    }
+
+    $wait_count = count($this->wait);
+    $hold_count = count($this->hold);
+
+    if (!$work_count && !$wait_count && $hold_count) {
+      throw new Exception(
+        pht(
+          'Future graph is stalled: some futures are held, but no futures '.
+          'are waiting or working. The graph can never resolve.'));
     }
 
-    $old = $this->work;
-    $this->work = array_slice($this->wait, 0, $this->limit, true);
+    // Figure out how many futures we can start. If we don't have a limit,
+    // we can start every waiting future. If we do have a limit, we can only
+    // start as many futures as we have slots for.
 
-    //  If we're using a limit, our futures are sleeping and need to be polled
-    //  to begin execution, so poll any futures which weren't in our working set
-    //  before.
-    foreach ($this->work as $work => $key) {
-      if (!isset($old[$work])) {
-        $this->futures[$key]->isReady();
+    if ($limit) {
+      $work_limit = min($limit, $wait_count);
+    } else {
+      $work_limit = $wait_count;
+    }
+
+    // If we're ready to start futures, start them now.
+
+    if ($work_limit) {
+      foreach ($this->wait as $future_key) {
+        $this->moveFutureToWork($future_key);
+
+        $work_limit--;
+        if (!$work_limit) {
+          return;
+        }
       }
     }
+
   }
 
+  private function canMoveFutureToWait($future_key) {
+    return true;
+  }
+
+  private function moveFutureToWait($future_key) {
+    unset($this->hold[$future_key]);
+    $this->wait[$future_key] = $future_key;
+  }
+
+  private function moveFutureToWork($future_key) {
+    unset($this->wait[$future_key]);
+    $this->work[$future_key] = $future_key;
+
+    $this->futures[$future_key]->startFuture();
+  }
+
+  private function moveFutureToDone($future_key) {
+    $this->key = $future_key;
+    unset($this->work[$future_key]);
+
+    // Before we return, do another working set update so we start any
+    // futures that are ready to go as soon as we can.
+
+    $this->updateWorkingSet();
+
+    $this->futures[$future_key]->endFuture();
+  }
 
   /**
    * Wait for activity on one of several sockets.
    *
    * @param  list  List of sockets expected to become readable.
    * @param  list  List of sockets expected to become writable.
    * @param  float Timeout, in seconds.
    * @return void
    */
   private function waitForSockets(
     array $read_list,
     array $write_list,
     $timeout = 1.0) {
 
     static $handler_installed = false;
 
     if (!$handler_installed) {
       // If we're spawning child processes, we need to install a signal handler
       // here to catch cases like execing '(sleep 60 &) &' where the child
       // exits but a socket is kept open. But we don't actually need to do
       // anything because the SIGCHLD will interrupt the stream_select(), as
       // long as we have a handler registered.
       if (function_exists('pcntl_signal')) {
         if (!pcntl_signal(SIGCHLD, array(__CLASS__, 'handleSIGCHLD'))) {
           throw new Exception(pht('Failed to install signal handler!'));
         }
       }
       $handler_installed = true;
     }
 
     $timeout_sec = (int)$timeout;
     $timeout_usec = (int)(1000000 * ($timeout - $timeout_sec));
 
     $exceptfds = array();
     $ok = @stream_select(
       $read_list,
       $write_list,
       $exceptfds,
       $timeout_sec,
       $timeout_usec);
 
     if ($ok === false) {
       // Hopefully, means we received a SIGCHLD. In the worst case, we degrade
       // to a busy wait.
     }
   }
 
   public static function handleSIGCHLD($signo) {
     // This function is a dummy, we just need to have some handler registered
     // so that PHP will get interrupted during "stream_select()". If we don't
     // register a handler, "stream_select()" won't fail.
   }
 
 
 }
diff --git a/src/future/exec/__tests__/ExecFutureTestCase.php b/src/future/exec/__tests__/ExecFutureTestCase.php
index e10a188a..572c5692 100644
--- a/src/future/exec/__tests__/ExecFutureTestCase.php
+++ b/src/future/exec/__tests__/ExecFutureTestCase.php
@@ -1,173 +1,173 @@
 <?php
 
 final class ExecFutureTestCase extends PhutilTestCase {
 
   public function testEmptyWrite() {
     // NOTE: This is mostly testing that we don't hang while doing an empty
     // write.
 
     list($stdout) = $this->newCat()
       ->write('')
       ->resolvex();
 
     $this->assertEqual('', $stdout);
   }
 
   private function newCat() {
     $bin = $this->getSupportExecutable('cat');
     return new ExecFuture('php -f %R', $bin);
   }
 
   private function newSleep($duration) {
     $bin = $this->getSupportExecutable('sleep');
     return new ExecFuture('php -f %R -- %s', $bin, $duration);
   }
 
   public function testKeepPipe() {
     // NOTE: This is mostly testing the semantics of $keep_pipe in write().
 
     list($stdout) = $this->newCat()
       ->write('', true)
       ->start()
       ->write('x', true)
       ->write('y', true)
       ->write('z', false)
       ->resolvex();
 
     $this->assertEqual('xyz', $stdout);
   }
 
   public function testLargeBuffer() {
     // NOTE: This is mostly a coverage test to hit branches where we're still
     // flushing a buffer.
 
     $data = str_repeat('x', 1024 * 1024 * 4);
     list($stdout) = $this->newCat()->write($data)->resolvex();
 
     $this->assertEqual($data, $stdout);
   }
 
   public function testBufferLimit() {
     $data = str_repeat('x', 1024 * 1024);
     list($stdout) = $this->newCat()
       ->setStdoutSizeLimit(1024)
       ->write($data)
       ->resolvex();
 
     $this->assertEqual(substr($data, 0, 1024), $stdout);
   }
 
   public function testResolveTimeoutTestShouldRunLessThan1Sec() {
     // NOTE: This tests interactions between the resolve() timeout and the
     // resolution timeout, which are somewhat similar but not identical.
 
-    $future = $this->newSleep(32000)->start();
+    $future = $this->newSleep(32000);
     $future->setTimeout(32000);
 
     // We expect this to return in 0.01s.
     $iterator = (new FutureIterator(array($future)))
       ->setUpdateInterval(0.01);
     foreach ($iterator as $resolved_result) {
       $result = $resolved_result;
       break;
     }
     $this->assertEqual($result, null);
 
     // We expect this to now force the time out / kill immediately. If we don't
     // do this, we'll hang when exiting until our subprocess exits (32000
     // seconds!)
     $future->setTimeout(0.01);
-    $future->resolve();
+    $iterator->resolveAll();
   }
 
   public function testTerminateWithoutStart() {
     // We never start this future, but it should be fine to kill a future from
     // any state.
     $future = $this->newSleep(1);
     $future->resolveKill();
 
     $this->assertTrue(true);
   }
 
   public function testTimeoutTestShouldRunLessThan1Sec() {
     // NOTE: This is partly testing that we choose appropriate select wait
     // times; this test should run for significantly less than 1 second.
 
     $future = $this->newSleep(32000);
     list($err) = $future->setTimeout(0.01)->resolve();
 
     $this->assertTrue($err > 0);
     $this->assertTrue($future->getWasKilledByTimeout());
   }
 
   public function testMultipleTimeoutsTestShouldRunLessThan1Sec() {
     $futures = array();
     for ($ii = 0; $ii < 4; $ii++) {
       $futures[] = $this->newSleep(32000)->setTimeout(0.01);
     }
 
     foreach (new FutureIterator($futures) as $future) {
       list($err) = $future->resolve();
 
       $this->assertTrue($err > 0);
       $this->assertTrue($future->getWasKilledByTimeout());
     }
   }
 
   public function testMultipleResolves() {
     // It should be safe to call resolve(), resolvex(), resolveKill(), etc.,
     // as many times as you want on the same process.
     $bin = $this->getSupportExecutable('echo');
 
     $future = new ExecFuture('php -f %R -- quack', $bin);
     $future->resolve();
     $future->resolvex();
     list($err) = $future->resolveKill();
 
     $this->assertEqual(0, $err);
   }
 
   public function testReadBuffering() {
     $str_len_8 = 'abcdefgh';
     $str_len_4 = 'abcd';
 
     // This is a write/read with no read buffer.
     $future = $this->newCat();
     $future->write($str_len_8);
 
     do {
       $future->isReady();
       list($read) = $future->read();
       if (strlen($read)) {
         break;
       }
     } while (true);
 
     // We expect to get the entire string back in the read.
     $this->assertEqual($str_len_8, $read);
     $future->resolve();
 
 
     // This is a write/read with a read buffer.
     $future = $this->newCat();
     $future->write($str_len_8);
 
     // Set the read buffer size.
     $future->setReadBufferSize(4);
     do {
       $future->isReady();
       list($read) = $future->read();
       if (strlen($read)) {
         break;
       }
     } while (true);
 
     // We expect to get the entire string back in the read.
     $this->assertEqual($str_len_4, $read);
 
     // Remove the limit so we can resolve the future.
     $future->setReadBufferSize(null);
     $future->resolve();
   }
 
 }
diff --git a/src/lint/linter/ArcanistFutureLinter.php b/src/lint/linter/ArcanistFutureLinter.php
index e9df8371..7fad5a55 100644
--- a/src/lint/linter/ArcanistFutureLinter.php
+++ b/src/lint/linter/ArcanistFutureLinter.php
@@ -1,56 +1,57 @@
 <?php
 
 abstract class ArcanistFutureLinter extends ArcanistLinter {
 
   private $futures;
 
   abstract protected function buildFutures(array $paths);
   abstract protected function resolveFuture($path, Future $future);
 
   final protected function getFuturesLimit() {
     return 8;
   }
 
   public function willLintPaths(array $paths) {
     $limit = $this->getFuturesLimit();
     $this->futures = id(new FutureIterator(array()))->limit($limit);
     foreach ($this->buildFutures($paths) as $path => $future) {
-      $this->futures->addFuture($future, $path);
+      $future->setFutureKey($path);
+      $this->futures->addFuture($future);
     }
   }
 
   final public function lintPath($path) {
     return;
   }
 
   public function didLintPaths(array $paths) {
     if (!$this->futures) {
       return;
     }
 
     $map = array();
     foreach ($this->futures as $path => $future) {
       $this->setActivePath($path);
       $this->resolveFuture($path, $future);
       $map[$path] = $future;
     }
     $this->futures = array();
 
     $this->didResolveLinterFutures($map);
   }
 
 
   /**
    * Hook for cleaning up resources.
    *
    * This is invoked after a block of futures resolve, and allows linters to
    * discard or clean up any shared resources they no longer need.
    *
    * @param map<string, Future> Map of paths to resolved futures.
    * @return void
    */
   protected function didResolveLinterFutures(array $futures) {
     return;
   }
 
 }