includes/libs/WaitConditionLoop.php

   1 <?php
   2 /**
   3  * Wait loop that reaches a condition or times out.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @author Aaron Schulz
  22  */
  23
  24 /**
  25  * Wait loop that reaches a condition or times out
  26  * @since 1.28
  27  */
  28 class WaitConditionLoop {
  29         /** @var callable */
  30         private $condition;
  31         /** @var callable[] */
  32         private $busyCallbacks = [];
  33         /** @var float Seconds */
  34         private $timeout;
  35         /** @var float Seconds */
  36         private $lastWaitTime;
  37
  38         const CONDITION_REACHED = 1;
  39         const CONDITION_CONTINUE = 0; // evaluates as falsey
  40         const CONDITION_FAILED = -1;
  41         const CONDITION_TIMED_OUT = -2;
  42         const CONDITION_ABORTED = -3;
  43
  44         /**
  45          * @param callable $condition Callback that returns a WaitConditionLoop::CONDITION_ constant
  46          * @param float $timeout Timeout in seconds
  47          * @param array &$busyCallbacks List of callbacks to do useful work (by reference)
  48          */
  49         public function __construct( callable $condition, $timeout = 5.0, &$busyCallbacks = [] ) {
  50                 $this->condition = $condition;
  51                 $this->timeout = $timeout;
  52                 $this->busyCallbacks =& $busyCallbacks;
  53         }
  54
  55         /**
  56          * Invoke the loop and continue until either:
  57          *   - a) The condition callback returns neither CONDITION_CONTINUE nor false
  58          *   - b) The timeout is reached
  59          * This a condition callback can return true (stop) or false (continue) for convenience.
  60          * In such cases, the halting result of "true" will be converted to CONDITION_REACHED.
  61          *
  62          * If $timeout is 0, then only the condition callback will be called (no busy callbacks),
  63          * and this will immediately return CONDITION_FAILED if the condition was not met.
  64          *
  65          * Exceptions in callbacks will be caught and the callback will be swapped with
  66          * one that simply rethrows that exception back to the caller when invoked.
  67          *
  68          * @return integer WaitConditionLoop::CONDITION_* constant
  69          * @throws Exception Any error from the condition callback
  70          */
  71         public function invoke() {
  72                 $elapsed = 0.0; // seconds
  73                 $sleepUs = 0; // microseconds to sleep each time
  74                 $lastCheck = false;
  75                 $finalResult = self::CONDITION_TIMED_OUT;
  76                 do {
  77                         $checkStartTime = $this->getWallTime();
  78                         // Check if the condition is met yet
  79                         $realStart = $this->getWallTime();
  80                         $cpuStart = $this->getCpuTime();
  81                         $checkResult = call_user_func( $this->condition );
  82                         $cpu = $this->getCpuTime() - $cpuStart;
  83                         $real = $this->getWallTime() - $realStart;
  84                         // Exit if the condition is reached, and error occurs, or this is non-blocking
  85                         if ( $this->timeout <= 0 ) {
  86                                 $finalResult = $checkResult ? self::CONDITION_REACHED : self::CONDITION_FAILED;
  87                                 break;
  88                         } elseif ( (int)$checkResult !== self::CONDITION_CONTINUE ) {
  89                                 if ( is_int( $checkResult ) ) {
  90                                         $finalResult = $checkResult;
  91                                 } else {
  92                                         $finalResult = self::CONDITION_REACHED;
  93                                 }
  94                                 break;
  95                         } elseif ( $lastCheck ) {
  96                                 break; // timeout reached
  97                         }
  98                         // Detect if condition callback seems to block or if justs burns CPU
  99                         $conditionUsesInterrupts = ( $real > 0.100 && $cpu <= $real * .03 );
 100                         if ( !$this->popAndRunBusyCallback() && !$conditionUsesInterrupts ) {
 101                                 // 10 queries = 10(10+100)/2 ms = 550ms, 14 queries = 1050ms
 102                                 $sleepUs = min( $sleepUs + 10 * 1e3, 1e6 ); // stop incrementing at ~1s
 103                                 $this->usleep( $sleepUs );
 104                         }
 105                         $checkEndTime = $this->getWallTime();
 106                         // The max() protects against the clock getting set back
 107                         $elapsed += max( $checkEndTime - $checkStartTime, 0.010 );
 108                         // Do not let slow callbacks timeout without checking the condition one more time
 109                         $lastCheck = ( $elapsed >= $this->timeout );
 110                 } while ( true );
 111
 112                 $this->lastWaitTime = $elapsed;
 113
 114                 return $finalResult;
 115         }
 116
 117         /**
 118          * @return float Seconds
 119          */
 120         public function getLastWaitTime() {
 121                 return $this->lastWaitTime;
 122         }
 123
 124         /**
 125          * @param integer $microseconds
 126          */
 127         protected function usleep( $microseconds ) {
 128                 usleep( $microseconds );
 129         }
 130
 131         /**
 132          * @return float
 133          */
 134         protected function getWallTime() {
 135                 return microtime( true );
 136         }
 137
 138         /**
 139          * @return float Returns 0.0 if not supported (Windows on PHP < 7)
 140          */
 141         protected function getCpuTime() {
 142                 $time = 0.0;
 143
 144                 if ( defined( 'HHVM_VERSION' ) && PHP_OS === 'Linux' ) {
 145                         $ru = getrusage( 2 /* RUSAGE_THREAD */ );
 146                 } else {
 147                         $ru = getrusage( 0 /* RUSAGE_SELF */ );
 148                 }
 149                 if ( $ru ) {
 150                         $time += $ru['ru_utime.tv_sec'] + $ru['ru_utime.tv_usec'] / 1e6;
 151                         $time += $ru['ru_stime.tv_sec'] + $ru['ru_stime.tv_usec'] / 1e6;
 152                 }
 153
 154                 return $time;
 155         }
 156
 157         /**
 158          * Run one of the callbacks that does work ahead of time for another caller
 159          *
 160          * @return bool Whether a callback was executed
 161          */
 162         private function popAndRunBusyCallback() {
 163                 if ( $this->busyCallbacks ) {
 164                         reset( $this->busyCallbacks );
 165                         $key = key( $this->busyCallbacks );
 166                         /** @var callable $workCallback */
 167                         $workCallback =& $this->busyCallbacks[$key];
 168                         try {
 169                                 $workCallback();
 170                         } catch ( Exception $e ) {
 171                                 $workCallback = function () use ( $e ) {
 172                                         throw $e;
 173                                 };
 174                         }
 175                         unset( $this->busyCallbacks[$key] ); // consume
 176
 177                         return true;
 178                 }
 179
 180                 return false;
 181         }
 182 }