Convert taskmasters to use an autoscale pool

Summary: Ref T7352. This is pretty straightforward. I renamed `phd.start-taskmasters` to `phd.taskmasters` for clarity.

Test Plan:
  - Ran `phd start`, `phd start --autoscale-reserve 0.25`, `phd restart --autoscale-reserve 0.25`, etc.
  - Examined PID file to see options were passed.
  - I'm defaulting this off (0 reserve) and making it a flag rather than an option because it's a very advanced feature which is probably not useful outside of instancing.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7352

Differential Revision: https://secure.phabricator.com/D11871

src/applications/config/check/PhabricatorExtraConfigSetupCheck.php

@@ -208,6 +208,9 @@ final class PhabricatorExtraConfigSetupCheck extends PhabricatorSetupCheck {
         'longer used or supported.'),
       'config.mask' => pht(
         'Use `config.hide` instead of this option.'),
+      'phd.start-taskmasters' => pht(
+        'Taskmasters now use an autoscaling pool. You can configure the '.
+        'pool size with `phd.taskmasters`.'),
     );
 
     return $ancient_config;

src/applications/config/option/PhabricatorPHDConfigOptions.php

@@ -29,13 +29,13 @@ final class PhabricatorPHDConfigOptions
         ->setDescription(
           pht(
             'Directory that the daemons should use to store log files.')),
-      $this->newOption('phd.start-taskmasters', 'int', 4)
-        ->setSummary(pht('Number of TaskMaster daemons to start by default.'))
+      $this->newOption('phd.taskmasters', 'int', 4)
+        ->setSummary(pht('Maximum taskmaster daemon pool size.'))
         ->setDescription(
           pht(
-            "Number of 'TaskMaster' daemons that 'phd start' should start. ".
-            "You can raise this if you have a task backlog, or explicitly ".
-            "launch more with 'phd launch <N> taskmaster'.")),
+            'Maximum number of taskmaster daemons to run at once. Raising '.
+            'this can increase the maximum throughput of the task queue. The '.
+            'pool will automatically scale down when unutilized.')),
       $this->newOption('phd.verbose', 'bool', false)
         ->setBoolOptions(
           array(

src/applications/daemon/management/PhabricatorDaemonManagementRestartWorkflow.php

@@ -31,6 +31,7 @@ final class PhabricatorDaemonManagementRestartWorkflow
               'Also stop running processes that look like daemons but do '.
               'not have corresponding PID files.'),
           ),
+          $this->getAutoscaleReserveArgument(),
         ));
   }
 
@@ -46,7 +47,10 @@ final class PhabricatorDaemonManagementRestartWorkflow
       return $err;
     }
 
-    return $this->executeStartCommand();
+    return $this->executeStartCommand(
+      array(
+        'reserve' => (float)$args->getArg('autoscale-reserve', 0.0),
+      ));
   }
 
 }

src/applications/daemon/management/PhabricatorDaemonManagementStartWorkflow.php

@@ -24,13 +24,17 @@ final class PhabricatorDaemonManagementStartWorkflow
             'help' => pht(
               'Start daemons even if daemons are already running.'),
           ),
+          $this->getAutoscaleReserveArgument(),
         ));
   }
 
   public function execute(PhutilArgumentParser $args) {
     return $this->executeStartCommand(
-      $args->getArg('keep-leases'),
-      $args->getArg('force'));
+      array(
+        'keep-leases' => $args->getArg('keep-leases'),
+        'force' => $args->getArg('force'),
+        'reserve' => (float)$args->getArg('autoscale-reserve', 0.0),
+      ));
   }
 
 }

src/applications/daemon/management/PhabricatorDaemonManagementWorkflow.php

@@ -290,10 +290,18 @@ abstract class PhabricatorDaemonManagementWorkflow
 /* -(  Commands  )----------------------------------------------------------- */
 
 
-  protected final function executeStartCommand($keep_leases, $force) {
+  protected final function executeStartCommand(array $options) {
+    PhutilTypeSpec::checkMap(
+      $options,
+      array(
+        'keep-leases' => 'optional bool',
+        'force' => 'optional bool',
+        'reserve' => 'optional float',
+      ));
+
     $console = PhutilConsole::getConsole();
 
-    if (!$force) {
+    if (!idx($options, 'force')) {
       $running = $this->loadRunningDaemons();
 
       // This may include daemons which were launched but which are no longer
@@ -315,7 +323,7 @@ abstract class PhabricatorDaemonManagementWorkflow
       }
     }
 
-    if ($keep_leases) {
+    if (idx($options, 'keep-leases')) {
       $console->writeErr("%s\n", pht('Not touching active task queue leases.'));
     } else {
       $console->writeErr("%s\n", pht('Freeing active task leases...'));
@@ -335,14 +343,15 @@ abstract class PhabricatorDaemonManagementWorkflow
       array(
         'class' => 'PhabricatorTriggerDaemon',
       ),
-    );
-
-    $taskmasters = PhabricatorEnv::getEnvConfig('phd.start-taskmasters');
-    for ($ii = 0; $ii < $taskmasters; $ii++) {
-      $daemons[] = array(
+      array(
         'class' => 'PhabricatorTaskmasterDaemon',
-      );
-    }
+        'autoscale' => array(
+          'group' => 'task',
+          'pool' => PhabricatorEnv::getEnvConfig('phd.taskmasters'),
+          'reserve' => idx($options, 'reserve', 0),
+        ),
+      ),
+    );
 
     $this->launchDaemons($daemons, $is_debug = false);
 
@@ -577,7 +586,13 @@ abstract class PhabricatorDaemonManagementWorkflow
     foreach ($daemons as $daemon) {
       $is_autoscale = isset($daemon['autoscale']['group']);
       if ($is_autoscale) {
-        $autoscale = pht('(Autoscaling)');
+        $autoscale = $daemon['autoscale'];
+        foreach ($autoscale as $key => $value) {
+          $autoscale[$key] = $key.'='.$value;
+        }
+        $autoscale = implode(', ', $autoscale);
+
+        $autoscale = pht('(Autoscaling: %s)', $autoscale);
       } else {
         $autoscale = pht('(Static)');
       }
@@ -591,4 +606,16 @@ abstract class PhabricatorDaemonManagementWorkflow
     $console->writeOut("\n");
   }
 
+  protected function getAutoscaleReserveArgument() {
+    return array(
+      'name' => 'autoscale-reserve',
+      'param' => 'ratio',
+      'help' => pht(
+        'Specify a proportion of machine memory which must be free '.
+        'before autoscale pools will grow. For example, a value of 0.25 '.
+        'means that pools will not grow unless the machine has at least '.
+        '25%% of its RAM free.'),
+    );
+  }
+
 }

src/docs/user/configuration/managing_daemons.diviner

@@ -99,8 +99,9 @@ This daemon will daemonize and run normally.
 
 == General Tips ==
 
-  - You can set the number of taskmasters that `phd start` starts by the config
-    key `phd.start-taskmasters`. If you have a task backlog, try increasing it.
+  - You can set the maximum number of taskmasters that will run at once
+    by adjusting `phd.taskmasters`. If you have a task backlog, try increasing
+    it.
   - When you `phd launch` or `phd debug` a daemon, you can type any unique
     substring of its name, so `phd launch pull` will work correctly.
   - `phd stop` and `phd restart` stop **all** of the daemons on the machine, not

src/infrastructure/daemon/workers/PhabricatorTaskmasterDaemon.php

@@ -3,9 +3,6 @@
 final class PhabricatorTaskmasterDaemon extends PhabricatorDaemon {
 
   protected function run() {
-    $taskmaster_count = PhabricatorEnv::getEnvConfig('phd.start-taskmasters');
-    $offset = mt_rand(0, $taskmaster_count - 1);
-
     do {
       $tasks = id(new PhabricatorWorkerLeaseQuery())
         ->setLimit(1)
@@ -44,22 +41,11 @@ final class PhabricatorTaskmasterDaemon extends PhabricatorDaemon {
 
         $sleep = 0;
       } else {
-        // When there's no work, sleep for as many seconds as there are
-        // active taskmasters.
-
-        // On average, this starts tasks added to an empty queue after one
-        // second. This keeps responsiveness high even on small instances
-        // without much work to do.
-
-        // It also means an empty queue has an average load of one query
-        // per second even if there are a very large number of taskmasters
-        // launched.
-
-        // The first time we sleep, we add a random offset to try to spread
-        // the sleep times out somewhat evenly.
+        // When there's no work, sleep for one second. The pool will
+        // autoscale down if we're continuously idle for an extended period
+        // of time.
         $this->willBeginIdle();
-        $sleep = $taskmaster_count + $offset;
-        $offset = 0;
+        $sleep = 1;
       }
 
       $this->sleep($sleep);