diff --git a/src/applications/config/option/PhabricatorDeveloperConfigOptions.php b/src/applications/config/option/PhabricatorDeveloperConfigOptions.php
index 9f26ba6bb2..0c6426c39e 100644
--- a/src/applications/config/option/PhabricatorDeveloperConfigOptions.php
+++ b/src/applications/config/option/PhabricatorDeveloperConfigOptions.php
@@ -1,127 +1,152 @@
 <?php
 
 final class PhabricatorDeveloperConfigOptions
   extends PhabricatorApplicationConfigOptions {
 
   public function getName() {
     return pht('Developer / Debugging');
   }
 
   public function getDescription() {
     return pht('Options for Phabricator developers, including debugging.');
   }
 
   public function getOptions() {
     return array(
       $this->newOption('darkconsole.enabled', 'bool', false)
         ->setBoolOptions(
           array(
             pht('Enable DarkConsole'),
             pht('Disable DarkConsole'),
           ))
         ->setSummary(pht("Enable Phabricator's debugging console."))
         ->setDescription(
           pht(
             "DarkConsole is a development and profiling tool built into ".
             "Phabricator's web interface. You should leave it disabled unless ".
             "you are developing or debugging Phabricator.\n\n".
             "Once you activate DarkConsole for the install, **you need to ".
             "enable it for your account before it will actually appear on ".
             "pages.** You can do this in Settings > Developer Settings.\n\n".
             "DarkConsole exposes potentially sensitive data (like queries, ".
             "stack traces, and configuration) so you generally should not ".
             "turn it on in production.")),
       $this->newOption('darkconsole.always-on', 'bool', false)
         ->setBoolOptions(
           array(
             pht('Always Activate DarkConsole'),
             pht('Require DarkConsole Activation'),
           ))
         ->setSummary(pht('Activate DarkConsole on every page.'))
         ->setDescription(
           pht(
             "This option allows you to enable DarkConsole on every page, ".
             "even for logged-out users. This is only really useful if you ".
             "need to debug something on a logged-out page. You should not ".
             "enable this option in production.\n\n".
             "You must enable DarkConsole by setting {{darkconsole.enabled}} ".
             "before this option will have any effect.")),
+      $this->newOption('debug.time-limit', 'int', null)
+        ->setSummary(
+          pht(
+            'Limit page execution time to debug hangs.'))
+        ->setDescription(
+          pht(
+            "This option can help debug pages which are taking a very ".
+            "long time (more than 30 seconds) to render.\n\n".
+            "If a page is slow to render (but taking less than 30 seconds), ".
+            "the best tools to use to figure out why it is slow are usually ".
+            "the DarkConsole service call profiler and XHProf.\n\n".
+            "However, if a request takes a very long time to return, some ".
+            "components (like Apache, nginx, or PHP itself) may abort the ".
+            "request before it finishes. This can prevent you from using ".
+            "profiling tools to understand page performance in detail.\n\n".
+            "In these cases, you can use this option to force the page to ".
+            "abort after a smaller number of seconds (for example, 10), and ".
+            "dump a useful stack trace. This can provide useful information ".
+            "about why a page is hanging.\n\n".
+            "To use this option, set it to a small number (like 10), and ".
+            "reload a hanging page. The page should exit after 10 seconds ".
+            "and give you a stack trace.\n\n".
+            "You should turn this option off (set it to 0) when you are ".
+            "done with it. Leaving it on creates a small amount of overhead ".
+            "for all requests, even if they do not hit the time limit.")),
       $this->newOption('debug.stop-on-redirect', 'bool', false)
         ->setBoolOptions(
           array(
             pht('Stop Before HTTP Redirect'),
             pht('Use Normal HTTP Redirects'),
           ))
         ->setSummary(
           pht(
             'Confirm before redirecting so DarkConsole can be examined.'))
         ->setDescription(
           pht(
             'Normally, Phabricator issues HTTP redirects after a successful '.
             'POST. This can make it difficult to debug things which happen '.
             'while processing the POST, because service and profiling '.
             'information are lost. By setting this configuration option, '.
             'Phabricator will show a page instead of automatically '.
             'redirecting, allowing you to examine service and profiling '.
             'information. It also makes the UX awful, so you should only '.
             'enable it when debugging.')),
       $this->newOption('debug.profile-rate', 'int', 0)
         ->addExample(0,     pht('No profiling'))
         ->addExample(1,     pht('Profile every request (slow)'))
         ->addExample(1000,  pht('Profile 0.1%% of all requests'))
         ->setSummary(pht('Automatically profile some percentage of pages.'))
         ->setDescription(
           pht(
             "Normally, Phabricator profiles pages only when explicitly ".
             "requested via DarkConsole. However, it may be useful to profile ".
             "some pages automatically.\n\n".
             "Set this option to a positive integer N to profile 1 / N pages ".
             "automatically. For example, setting it to 1 will profile every ".
             "page, while setting it to 1000 will profile 1 page per 1000 ".
             "requests (i.e., 0.1%% of requests).\n\n".
             "Since profiling is slow and generates a lot of data, you should ".
             "set this to 0 in production (to disable it) or to a large number ".
             "(to collect a few samples, if you're interested in having some ".
             "data to look at eventually). In development, it may be useful to ".
             "set it to 1 in order to debug performance problems.\n\n".
             "NOTE: You must install XHProf for profiling to work.")),
       $this->newOption('phabricator.developer-mode', 'bool', false)
         ->setBoolOptions(
           array(
             pht('Enable developer mode'),
             pht('Disable developer mode'),
           ))
           ->setSummary(pht('Enable verbose error reporting and disk reads.'))
           ->setDescription(
             pht(
               'This option enables verbose error reporting (stack traces, '.
               'error callouts) and forces disk reads of static assets on '.
               'every reload.')),
       $this->newOption('celerity.minify', 'bool', true)
         ->setBoolOptions(
           array(
             pht('Minify static resources.'),
             pht("Don't minify static resources."),
           ))
         ->setSummary(pht('Minify static Celerity resources.'))
         ->setDescription(
           pht(
             'Minify static resources by removing whitespace and comments. You '.
             'should enable this in production, but disable it in '.
             'development.')),
       $this->newOption('cache.enable-deflate', 'bool', true)
         ->setBoolOptions(
           array(
             pht('Enable deflate compression'),
             pht('Disable deflate compression'),
           ))
         ->setSummary(
           pht('Toggle gzdeflate()-based compression for some caches.'))
         ->setDescription(
           pht(
             'Set this to false to disable the use of gzdeflate()-based '.
             'compression in some caches. This may give you less performant '.
             '(but more debuggable) caching.')),
     );
   }
 }
diff --git a/support/PhabricatorStartup.php b/support/PhabricatorStartup.php
index 3270cb8e00..62b28c85c5 100644
--- a/support/PhabricatorStartup.php
+++ b/support/PhabricatorStartup.php
@@ -1,790 +1,855 @@
 <?php
 
 /**
  * Handle request startup, before loading the environment or libraries. This
  * class bootstraps the request state up to the point where we can enter
  * Phabricator code.
  *
  * NOTE: This class MUST NOT have any dependencies. It runs before libraries
  * load.
  *
  * Rate Limiting
  * =============
  *
  * Phabricator limits the rate at which clients can request pages, and issues
  * HTTP 429 "Too Many Requests" responses if clients request too many pages too
  * quickly. Although this is not a complete defense against high-volume attacks,
  * it can  protect an install against aggressive crawlers, security scanners,
  * and some types of malicious activity.
  *
  * To perform rate limiting, each page increments a score counter for the
  * requesting user's IP. The page can give the IP more points for an expensive
  * request, or fewer for an authetnicated request.
  *
  * Score counters are kept in buckets, and writes move to a new bucket every
  * minute. After a few minutes (defined by @{method:getRateLimitBucketCount}),
  * the oldest bucket is discarded. This provides a simple mechanism for keeping
  * track of scores without needing to store, access, or read very much data.
  *
  * Users are allowed to accumulate up to 1000 points per minute, averaged across
  * all of the tracked buckets.
  *
  * @task info         Accessing Request Information
  * @task hook         Startup Hooks
  * @task apocalypse   In Case Of Apocalypse
  * @task validation   Validation
  * @task ratelimit    Rate Limiting
  */
 final class PhabricatorStartup {
 
   private static $startTime;
+  private static $debugTimeLimit;
   private static $globals = array();
   private static $capturingOutput;
   private static $rawInput;
   private static $oldMemoryLimit;
 
   // TODO: For now, disable rate limiting entirely by default. We need to
   // iterate on it a bit for Conduit, some of the specific score levels, and
   // to deal with NAT'd offices.
   private static $maximumRate = 0;
 
 
 /* -(  Accessing Request Information  )-------------------------------------- */
 
 
   /**
    * @task info
    */
   public static function getStartTime() {
     return self::$startTime;
   }
 
 
   /**
    * @task info
    */
   public static function getMicrosecondsSinceStart() {
     return (int)(1000000 * (microtime(true) - self::getStartTime()));
   }
 
 
   /**
    * @task info
    */
   public static function setGlobal($key, $value) {
     self::validateGlobal($key);
 
     self::$globals[$key] = $value;
   }
 
 
   /**
    * @task info
    */
   public static function getGlobal($key, $default = null) {
     self::validateGlobal($key);
 
     if (!array_key_exists($key, self::$globals)) {
       return $default;
     }
 
     return self::$globals[$key];
   }
 
   /**
    * @task info
    */
   public static function getRawInput() {
     return self::$rawInput;
   }
 
 
 /* -(  Startup Hooks  )------------------------------------------------------ */
 
 
   /**
    * @task hook
    */
   public static function didStartup() {
     self::$startTime = microtime(true);
     self::$globals = array();
 
     static $registered;
     if (!$registered) {
       // NOTE: This protects us against multiple calls to didStartup() in the
       // same request, but also against repeated requests to the same
       // interpreter state, which we may implement in the future.
       register_shutdown_function(array(__CLASS__, 'didShutdown'));
       $registered = true;
     }
 
     self::setupPHP();
     self::verifyPHP();
 
     if (isset($_SERVER['REMOTE_ADDR'])) {
       self::rateLimitRequest($_SERVER['REMOTE_ADDR']);
     }
 
     self::normalizeInput();
 
     self::verifyRewriteRules();
 
     self::detectPostMaxSizeTriggered();
 
     self::beginOutputCapture();
 
     self::$rawInput = (string)file_get_contents('php://input');
   }
 
 
   /**
    * @task hook
    */
   public static function didShutdown() {
     $event = error_get_last();
 
     if (!$event) {
       return;
     }
 
     switch ($event['type']) {
       case E_ERROR:
       case E_PARSE:
       case E_COMPILE_ERROR:
         break;
       default:
         return;
     }
 
     $msg = ">>> UNRECOVERABLE FATAL ERROR <<<\n\n";
     if ($event) {
       // Even though we should be emitting this as text-plain, escape things
       // just to be sure since we can't really be sure what the program state
       // is when we get here.
       $msg .= htmlspecialchars(
         $event['message']."\n\n".$event['file'].':'.$event['line'],
         ENT_QUOTES,
         'UTF-8');
     }
 
     // flip dem tables
     $msg .= "\n\n\n";
     $msg .= "\xe2\x94\xbb\xe2\x94\x81\xe2\x94\xbb\x20\xef\xb8\xb5\x20\xc2\xaf".
             "\x5c\x5f\x28\xe3\x83\x84\x29\x5f\x2f\xc2\xaf\x20\xef\xb8\xb5\x20".
             "\xe2\x94\xbb\xe2\x94\x81\xe2\x94\xbb";
 
     self::didFatal($msg);
   }
 
   public static function loadCoreLibraries() {
     $phabricator_root = dirname(dirname(__FILE__));
     $libraries_root = dirname($phabricator_root);
 
     $root = null;
     if (!empty($_SERVER['PHUTIL_LIBRARY_ROOT'])) {
       $root = $_SERVER['PHUTIL_LIBRARY_ROOT'];
     }
 
     ini_set(
       'include_path',
       $libraries_root.PATH_SEPARATOR.ini_get('include_path'));
 
     @include_once $root.'libphutil/src/__phutil_library_init__.php';
     if (!@constant('__LIBPHUTIL__')) {
       self::didFatal(
         "Unable to load libphutil. Put libphutil/ next to phabricator/, or ".
         "update your PHP 'include_path' to include the parent directory of ".
         "libphutil/.");
     }
 
     phutil_load_library('arcanist/src');
 
     // Load Phabricator itself using the absolute path, so we never end up doing
     // anything surprising (loading index.php and libraries from different
     // directories).
     phutil_load_library($phabricator_root.'/src');
   }
 
 /* -(  Output Capture  )----------------------------------------------------- */
 
 
   public static function beginOutputCapture() {
     if (self::$capturingOutput) {
       self::didFatal('Already capturing output!');
     }
     self::$capturingOutput = true;
     ob_start();
   }
 
 
   public static function endOutputCapture() {
     if (!self::$capturingOutput) {
       return null;
     }
     self::$capturingOutput = false;
     return ob_get_clean();
   }
 
 
+/* -(  Debug Time Limit  )--------------------------------------------------- */
+
+
+  /**
+   * Set a time limit (in seconds) for the current script. After time expires,
+   * the script fatals.
+   *
+   * This works like `max_execution_time`, but prints out a useful stack trace
+   * when the time limit expires. This is primarily intended to make it easier
+   * to debug pages which hang by allowing extraction of a stack trace: set a
+   * short debug limit, then use the trace to figure out what's happening.
+   *
+   * The limit is implemented with a tick function, so enabling it implies
+   * some accounting overhead.
+   *
+   * @param int Time limit in seconds.
+   * @return void
+   */
+  public static function setDebugTimeLimit($limit) {
+    self::$debugTimeLimit = $limit;
+
+    static $initialized;
+    if (!$initialized) {
+      declare(ticks=1);
+      register_tick_function(array('PhabricatorStartup', 'onDebugTick'));
+    }
+  }
+
+
+  /**
+   * Callback tick function used by @{method:setDebugTimeLimit}.
+   *
+   * Fatals with a useful stack trace after the time limit expires.
+   *
+   * @return void
+   */
+  public static function onDebugTick() {
+    $limit = self::$debugTimeLimit;
+    if (!$limit) {
+      return;
+    }
+
+    $elapsed = (microtime(true) - self::getStartTime());
+    if ($elapsed > $limit) {
+      $frames = array();
+      foreach (debug_backtrace() as $frame) {
+        $file = isset($frame['file']) ? $frame['file'] : '-';
+        $file = basename($file);
+
+        $line = isset($frame['line']) ? $frame['line'] : '-';
+        $class = isset($frame['class']) ? $frame['class'].'->' : null;
+        $func = isset($frame['function']) ? $frame['function'].'()' : '?';
+
+        $frames[] = "{$file}:{$line} {$class}{$func}";
+      }
+
+      self::didFatal(
+        "Request aborted by debug time limit after {$limit} seconds.\n\n".
+        "STACK TRACE\n".
+        implode("\n", $frames));
+    }
+  }
+
+
 /* -(  In Case of Apocalypse  )---------------------------------------------- */
 
 
   /**
    * Fatal the request completely in response to an exception, sending a plain
    * text message to the client. Calls @{method:didFatal} internally.
    *
    * @param   string    Brief description of the exception context, like
    *                    `"Rendering Exception"`.
    * @param   Exception The exception itself.
    * @param   bool      True if it's okay to show the exception's stack trace
    *                    to the user. The trace will always be logged.
    * @return  exit      This method **does not return**.
    *
    * @task apocalypse
    */
   public static function didEncounterFatalException(
     $note,
     Exception $ex,
     $show_trace) {
 
     $message = '['.$note.'/'.get_class($ex).'] '.$ex->getMessage();
 
     $full_message = $message;
     $full_message .= "\n\n";
     $full_message .= $ex->getTraceAsString();
 
     if ($show_trace) {
       $message = $full_message;
     }
 
     self::didFatal($message, $full_message);
   }
 
 
   /**
    * Fatal the request completely, sending a plain text message to the client.
    *
    * @param   string  Plain text message to send to the client.
    * @param   string  Plain text message to send to the error log. If not
    *                  provided, the client message is used. You can pass a more
    *                  detailed message here (e.g., with stack traces) to avoid
    *                  showing it to users.
    * @return  exit    This method **does not return**.
    *
    * @task apocalypse
    */
   public static function didFatal($message, $log_message = null) {
     if ($log_message === null) {
       $log_message = $message;
     }
 
     self::endOutputCapture();
     $access_log = self::getGlobal('log.access');
 
     if ($access_log) {
       // We may end up here before the access log is initialized, e.g. from
       // verifyPHP().
       $access_log->setData(
         array(
           'c' => 500,
         ));
       $access_log->write();
     }
 
     header(
       'Content-Type: text/plain; charset=utf-8',
       $replace = true,
       $http_error = 500);
 
     error_log($log_message);
     echo $message;
 
     exit(1);
   }
 
 
 /* -(  Validation  )--------------------------------------------------------- */
 
 
   /**
    * @task validation
    */
   private static function setupPHP() {
     error_reporting(E_ALL | E_STRICT);
     self::$oldMemoryLimit = ini_get('memory_limit');
     ini_set('memory_limit', -1);
 
     // If we have libxml, disable the incredibly dangerous entity loader.
     if (function_exists('libxml_disable_entity_loader')) {
       libxml_disable_entity_loader(true);
     }
   }
 
 
   /**
    * @task validation
    */
   public static function getOldMemoryLimit() {
     return self::$oldMemoryLimit;
   }
 
   /**
    * @task validation
    */
   private static function normalizeInput() {
     // Replace superglobals with unfiltered versions, disrespect php.ini (we
     // filter ourselves)
     $filter = array(INPUT_GET, INPUT_POST,
       INPUT_SERVER, INPUT_ENV, INPUT_COOKIE);
     foreach ($filter as $type) {
       $filtered = filter_input_array($type, FILTER_UNSAFE_RAW);
       if (!is_array($filtered)) {
         continue;
       }
       switch ($type) {
         case INPUT_SERVER:
           $_SERVER = array_merge($_SERVER, $filtered);
           break;
         case INPUT_GET:
           $_GET = array_merge($_GET, $filtered);
           break;
         case INPUT_COOKIE:
           $_COOKIE = array_merge($_COOKIE, $filtered);
           break;
         case INPUT_POST:
           $_POST = array_merge($_POST, $filtered);
           break;
         case INPUT_ENV;
           $_ENV = array_merge($_ENV, $filtered);
           break;
       }
     }
 
     // rebuild $_REQUEST, respecting order declared in ini files
     $order = ini_get('request_order');
     if (!$order) {
       $order = ini_get('variables_order');
     }
     if (!$order) {
       // $_REQUEST will be empty, leave it alone
       return;
     }
     $_REQUEST = array();
     for ($i = 0; $i < strlen($order); $i++) {
       switch ($order[$i]) {
         case 'G':
           $_REQUEST = array_merge($_REQUEST, $_GET);
           break;
         case 'P':
           $_REQUEST = array_merge($_REQUEST, $_POST);
           break;
         case 'C':
           $_REQUEST = array_merge($_REQUEST, $_COOKIE);
           break;
         default:
           // $_ENV and $_SERVER never go into $_REQUEST
           break;
       }
     }
   }
 
   /**
    * @task validation
    */
   private static function verifyPHP() {
     $required_version = '5.2.3';
     if (version_compare(PHP_VERSION, $required_version) < 0) {
       self::didFatal(
         "You are running PHP version '".PHP_VERSION."', which is older than ".
         "the minimum version, '{$required_version}'. Update to at least ".
         "'{$required_version}'.");
     }
 
     if (get_magic_quotes_gpc()) {
       self::didFatal(
         "Your server is configured with PHP 'magic_quotes_gpc' enabled. This ".
         "feature is 'highly discouraged' by PHP's developers and you must ".
         "disable it to run Phabricator. Consult the PHP manual for ".
         "instructions.");
     }
 
     if (extension_loaded('apc')) {
       $apc_version = phpversion('apc');
       $known_bad = array(
         '3.1.14' => true,
         '3.1.15' => true,
         '3.1.15-dev' => true,
       );
       if (isset($known_bad[$apc_version])) {
         self::didFatal(
           "You have APC {$apc_version} installed. This version of APC is ".
           "known to be bad, and does not work with Phabricator (it will ".
           "cause Phabricator to fatal unrecoverably with nonsense errors). ".
           "Downgrade to version 3.1.13.");
       }
     }
   }
 
 
   /**
    * @task validation
    */
   private static function verifyRewriteRules() {
     if (isset($_REQUEST['__path__']) && strlen($_REQUEST['__path__'])) {
       return;
     }
 
     if (php_sapi_name() == 'cli-server') {
       // Compatibility with PHP 5.4+ built-in web server.
       $url = parse_url($_SERVER['REQUEST_URI']);
       $_REQUEST['__path__'] = $url['path'];
       return;
     }
 
     if (!isset($_REQUEST['__path__'])) {
       self::didFatal(
         "Request parameter '__path__' is not set. Your rewrite rules ".
         "are not configured correctly.");
     }
 
     if (!strlen($_REQUEST['__path__'])) {
       self::didFatal(
         "Request parameter '__path__' is set, but empty. Your rewrite rules ".
         "are not configured correctly. The '__path__' should always ".
         "begin with a '/'.");
     }
   }
 
 
   /**
    * @task validation
    */
   private static function validateGlobal($key) {
     static $globals = array(
       'log.access' => true,
       'csrf.salt'  => true,
     );
 
     if (empty($globals[$key])) {
       throw new Exception("Access to unknown startup global '{$key}'!");
     }
   }
 
 
   /**
    * Detect if this request has had its POST data stripped by exceeding the
    * 'post_max_size' PHP configuration limit.
    *
    * PHP has a setting called 'post_max_size'. If a POST request arrives with
    * a body larger than the limit, PHP doesn't generate $_POST but processes
    * the request anyway, and provides no formal way to detect that this
    * happened.
    *
    * We can still read the entire body out of `php://input`. However according
    * to the documentation the stream isn't available for "multipart/form-data"
    * (on nginx + php-fpm it appears that it is available, though, at least) so
    * any attempt to generate $_POST would be fragile.
    *
    * @task validation
    */
   private static function detectPostMaxSizeTriggered() {
     // If this wasn't a POST, we're fine.
     if ($_SERVER['REQUEST_METHOD'] != 'POST') {
       return;
     }
 
     // If there's POST data, clearly we're in good shape.
     if ($_POST) {
       return;
     }
 
     // For HTML5 drag-and-drop file uploads, Safari submits the data as
     // "application/x-www-form-urlencoded". For most files this generates
     // something in POST because most files decode to some nonempty (albeit
     // meaningless) value. However, some files (particularly small images)
     // don't decode to anything. If we know this is a drag-and-drop upload,
     // we can skip this check.
     if (isset($_REQUEST['__upload__'])) {
       return;
     }
 
     // PHP generates $_POST only for two content types. This routing happens
     // in `main/php_content_types.c` in PHP. Normally, all forms use one of
     // these content types, but some requests may not -- for example, Firefox
     // submits files sent over HTML5 XMLHTTPRequest APIs with the Content-Type
     // of the file itself. If we don't have a recognized content type, we
     // don't need $_POST.
     //
     // NOTE: We use strncmp() because the actual content type may be something
     // like "multipart/form-data; boundary=...".
     //
     // NOTE: Chrome sometimes omits this header, see some discussion in T1762
     // and http://code.google.com/p/chromium/issues/detail?id=6800
     $content_type = isset($_SERVER['CONTENT_TYPE'])
       ? $_SERVER['CONTENT_TYPE']
       : '';
 
     $parsed_types = array(
       'application/x-www-form-urlencoded',
       'multipart/form-data',
     );
 
     $is_parsed_type = false;
     foreach ($parsed_types as $parsed_type) {
       if (strncmp($content_type, $parsed_type, strlen($parsed_type)) === 0) {
         $is_parsed_type = true;
         break;
       }
     }
 
     if (!$is_parsed_type) {
       return;
     }
 
     // Check for 'Content-Length'. If there's no data, we don't expect $_POST
     // to exist.
     $length = (int)$_SERVER['CONTENT_LENGTH'];
     if (!$length) {
       return;
     }
 
     // Time to fatal: we know this was a POST with data that should have been
     // populated into $_POST, but it wasn't.
 
     $config = ini_get('post_max_size');
     PhabricatorStartup::didFatal(
       "As received by the server, this request had a nonzero content length ".
       "but no POST data.\n\n".
       "Normally, this indicates that it exceeds the 'post_max_size' setting ".
       "in the PHP configuration on the server. Increase the 'post_max_size' ".
       "setting or reduce the size of the request.\n\n".
       "Request size according to 'Content-Length' was '{$length}', ".
       "'post_max_size' is set to '{$config}'.");
   }
 
 
 /* -(  Rate Limiting  )------------------------------------------------------ */
 
 
   /**
    * Adjust the permissible rate limit score.
    *
    * By default, the limit is `1000`. You can use this method to set it to
    * a larger or smaller value. If you set it to `2000`, users may make twice
    * as many requests before rate limiting.
    *
    * @param int Maximum score before rate limiting.
    * @return void
    * @task ratelimit
    */
   public static function setMaximumRate($rate) {
     self::$maximumRate = $rate;
   }
 
 
   /**
    * Check if the user (identified by `$user_identity`) has issued too many
    * requests recently. If they have, end the request with a 429 error code.
    *
    * The key just needs to identify the user. Phabricator uses both user PHIDs
    * and user IPs as keys, tracking logged-in and logged-out users separately
    * and enforcing different limits.
    *
    * @param   string  Some key which identifies the user making the request.
    * @return  void    If the user has exceeded the rate limit, this method
    *                  does not return.
    * @task ratelimit
    */
   public static function rateLimitRequest($user_identity) {
     if (!self::canRateLimit()) {
       return;
     }
 
     $score = self::getRateLimitScore($user_identity);
     if ($score > (self::$maximumRate * self::getRateLimitBucketCount())) {
       // Give the user some bonus points for getting rate limited. This keeps
       // bad actors who keep slamming the 429 page locked out completely,
       // instead of letting them get a burst of requests through every minute
       // after a bucket expires.
       self::addRateLimitScore($user_identity, 50);
       self::didRateLimit($user_identity);
     }
   }
 
 
   /**
    * Add points to the rate limit score for some user.
    *
    * If users have earned more than 1000 points per minute across all the
    * buckets they'll be locked out of the application, so awarding 1 point per
    * request roughly corresponds to allowing 1000 requests per second, while
    * awarding 50 points roughly corresponds to allowing 20 requests per second.
    *
    * @param string  Some key which identifies the user making the request.
    * @param float   The cost for this request; more points pushes them toward
    *                the limit faster.
    * @return void
    * @task ratelimit
    */
   public static function addRateLimitScore($user_identity, $score) {
     if (!self::canRateLimit()) {
       return;
     }
 
     $current = self::getRateLimitBucket();
 
     // There's a bit of a race here, if a second process reads the bucket before
     // this one writes it, but it's fine if we occasionally fail to record a
     // user's score. If they're making requests fast enough to hit rate
     // limiting, we'll get them soon.
 
     $bucket_key = self::getRateLimitBucketKey($current);
     $bucket = apc_fetch($bucket_key);
     if (!is_array($bucket)) {
       $bucket = array();
     }
 
     if (empty($bucket[$user_identity])) {
       $bucket[$user_identity] = 0;
     }
 
     $bucket[$user_identity] += $score;
     apc_store($bucket_key, $bucket);
   }
 
 
   /**
    * Determine if rate limiting is available.
    *
    * Rate limiting depends on APC, and isn't available unless the APC user
    * cache is available.
    *
    * @return bool True if rate limiting is available.
    * @task ratelimit
    */
   private static function canRateLimit() {
     if (!self::$maximumRate) {
       return false;
     }
 
     if (!function_exists('apc_fetch')) {
       return false;
     }
 
     return true;
   }
 
 
   /**
    * Get the current bucket for storing rate limit scores.
    *
    * @return int The current bucket.
    * @task ratelimit
    */
   private static function getRateLimitBucket() {
     return (int)(time() / 60);
   }
 
 
   /**
    * Get the total number of rate limit buckets to retain.
    *
    * @return int Total number of rate limit buckets to retain.
    * @task ratelimit
    */
   private static function getRateLimitBucketCount() {
     return 5;
   }
 
 
   /**
    * Get the APC key for a given bucket.
    *
    * @param int Bucket to get the key for.
    * @return string APC key for the bucket.
    * @task ratelimit
    */
   private static function getRateLimitBucketKey($bucket) {
     return 'rate:bucket:'.$bucket;
   }
 
 
   /**
    * Get the APC key for the smallest stored bucket.
    *
    * @return string APC key for the smallest stored bucket.
    * @task ratelimit
    */
   private static function getRateLimitMinKey() {
     return 'rate:min';
   }
 
 
   /**
    * Get the current rate limit score for a given user.
    *
    * @param string Unique key identifying the user.
    * @return float The user's current score.
    * @task ratelimit
    */
   private static function getRateLimitScore($user_identity) {
     $min_key = self::getRateLimitMinKey();
 
     // Identify the oldest bucket stored in APC.
     $cur = self::getRateLimitBucket();
     $min = apc_fetch($min_key);
 
     // If we don't have any buckets stored yet, store the current bucket as
     // the oldest bucket.
     if (!$min) {
       apc_store($min_key, $cur);
       $min = $cur;
     }
 
     // Destroy any buckets that are older than the minimum bucket we're keeping
     // track of. Under load this normally shouldn't do anything, but will clean
     // up an old bucket once per minute.
     $count = self::getRateLimitBucketCount();
     for ($cursor = $min; $cursor < ($cur - $count); $cursor++) {
       apc_delete(self::getRateLimitBucketKey($cursor));
       apc_store($min_key, $cursor + 1);
     }
 
     // Now, sum up the user's scores in all of the active buckets.
     $score = 0;
     for (; $cursor <= $cur; $cursor++) {
       $bucket = apc_fetch(self::getRateLimitBucketKey($cursor));
       if (isset($bucket[$user_identity])) {
         $score += $bucket[$user_identity];
       }
     }
 
     return $score;
   }
 
 
   /**
    * Emit an HTTP 429 "Too Many Requests" response (indicating that the user
    * has exceeded application rate limits) and exit.
    *
    * @return exit This method **does not return**.
    * @task ratelimit
    */
   private static function didRateLimit() {
     $message =
       "TOO MANY REQUESTS\n".
       "You are issuing too many requests too quickly.\n".
       "To adjust limits, see \"Configuring a Preamble Script\" in the ".
       "documentation.";
 
     header(
       'Content-Type: text/plain; charset=utf-8',
       $replace = true,
       $http_error = 429);
 
     echo $message;
 
     exit(1);
   }
 
 }
diff --git a/webroot/index.php b/webroot/index.php
index 8ce3bc5a36..05a19d5d6b 100644
--- a/webroot/index.php
+++ b/webroot/index.php
@@ -1,175 +1,181 @@
 <?php
 
 $phabricator_root = dirname(dirname(__FILE__));
 require_once $phabricator_root.'/support/PhabricatorStartup.php';
 
 // If the preamble script exists, load it.
 $preamble_path = $phabricator_root.'/support/preamble.php';
 if (file_exists($preamble_path)) {
   require_once $preamble_path;
 }
 
 PhabricatorStartup::didStartup();
 
 $show_unexpected_traces = false;
 try {
   PhabricatorStartup::loadCoreLibraries();
 
   PhabricatorEnv::initializeWebEnvironment();
+
+  $debug_time_limit = PhabricatorEnv::getEnvConfig('debug.time-limit');
+  if ($debug_time_limit) {
+    PhabricatorStartup::setDebugTimeLimit($debug_time_limit);
+  }
+
   $show_unexpected_traces = PhabricatorEnv::getEnvConfig(
     'phabricator.developer-mode');
 
   // This is the earliest we can get away with this, we need env config first.
   PhabricatorAccessLog::init();
   $access_log = PhabricatorAccessLog::getLog();
   PhabricatorStartup::setGlobal('log.access', $access_log);
   $access_log->setData(
     array(
       'R' => AphrontRequest::getHTTPHeader('Referer', '-'),
       'r' => idx($_SERVER, 'REMOTE_ADDR', '-'),
       'M' => idx($_SERVER, 'REQUEST_METHOD', '-'),
     ));
 
   DarkConsoleXHProfPluginAPI::hookProfiler();
   DarkConsoleErrorLogPluginAPI::registerErrorHandler();
 
   $sink = new AphrontPHPHTTPSink();
 
   $response = PhabricatorSetupCheck::willProcessRequest();
   if ($response) {
     PhabricatorStartup::endOutputCapture();
     $sink->writeResponse($response);
     return;
   }
 
   $host = AphrontRequest::getHTTPHeader('Host');
   $path = $_REQUEST['__path__'];
 
   switch ($host) {
     default:
       $config_key = 'aphront.default-application-configuration-class';
       $application = PhabricatorEnv::newObjectFromConfig($config_key);
       break;
   }
 
   $application->setHost($host);
   $application->setPath($path);
   $application->willBuildRequest();
   $request = $application->buildRequest();
 
   // Until an administrator sets "phabricator.base-uri", assume it is the same
   // as the request URI. This will work fine in most cases, it just breaks down
   // when daemons need to do things.
   $request_protocol = ($request->isHTTPS() ? 'https' : 'http');
   $request_base_uri = "{$request_protocol}://{$host}/";
   PhabricatorEnv::setRequestBaseURI($request_base_uri);
 
   $write_guard = new AphrontWriteGuard(array($request, 'validateCSRF'));
 
   $application->setRequest($request);
   list($controller, $uri_data) = $application->buildController();
 
   $access_log->setData(
     array(
       'U' => (string)$request->getRequestURI()->getPath(),
       'C' => get_class($controller),
     ));
 
   // If execution throws an exception and then trying to render that exception
   // throws another exception, we want to show the original exception, as it is
   // likely the root cause of the rendering exception.
   $original_exception = null;
   try {
     $response = $controller->willBeginExecution();
 
     if ($request->getUser() && $request->getUser()->getPHID()) {
       $access_log->setData(
         array(
           'u' => $request->getUser()->getUserName(),
           'P' => $request->getUser()->getPHID(),
         ));
     }
 
     if (!$response) {
       $controller->willProcessRequest($uri_data);
       $response = $controller->processRequest();
     }
   } catch (Exception $ex) {
     $original_exception = $ex;
     $response = $application->handleException($ex);
   }
 
   try {
     $response = $controller->didProcessRequest($response);
     $response = $application->willSendResponse($response, $controller);
     $response->setRequest($request);
 
     $unexpected_output = PhabricatorStartup::endOutputCapture();
     if ($unexpected_output) {
       $unexpected_output = "Unexpected output:\n\n{$unexpected_output}";
       phlog($unexpected_output);
 
       if ($response instanceof AphrontWebpageResponse) {
         echo phutil_tag(
           'div',
           array('style' =>
             'background: #eeddff;'.
             'white-space: pre-wrap;'.
             'z-index: 200000;'.
             'position: relative;'.
             'padding: 8px;'.
             'font-family: monospace'),
           $unexpected_output);
       }
     }
 
     $sink->writeResponse($response);
   } catch (Exception $ex) {
     $write_guard->dispose();
     $access_log->write();
     if ($original_exception) {
       $ex = new PhutilAggregateException(
         'Multiple exceptions during processing and rendering.',
         array(
           $original_exception,
           $ex,
         ));
     }
     PhabricatorStartup::didEncounterFatalException(
       'Rendering Exception',
       $ex,
       $show_unexpected_traces);
   }
 
   $write_guard->dispose();
 
   $access_log->setData(
     array(
       'c' => $response->getHTTPResponseCode(),
       'T' => PhabricatorStartup::getMicrosecondsSinceStart(),
     ));
 
   DarkConsoleXHProfPluginAPI::saveProfilerSample($access_log);
 
   // Add points to the rate limits for this request.
   if (isset($_SERVER['REMOTE_ADDR'])) {
     $user_ip = $_SERVER['REMOTE_ADDR'];
 
     // The base score for a request allows users to make 30 requests per
     // minute.
     $score = (1000 / 30);
 
     // If the user was logged in, let them make more requests.
     if ($request->getUser() && $request->getUser()->getPHID()) {
       $score = $score / 5;
     }
 
     PhabricatorStartup::addRateLimitScore($user_ip, $score);
   }
 
 } catch (Exception $ex) {
   PhabricatorStartup::didEncounterFatalException(
     'Core Exception',
     $ex,
     $show_unexpected_traces);
 }