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_TIMED_OUT = -1;
  41         const CONDITION_ABORTED = -2;
  42
  43         /**
  44          * @param callable $condition Callback that returns a WaitConditionLoop::CONDITION_ constant
  45          * @param float $timeout Timeout in seconds
  46          * @param array &$busyCallbacks List of callbacks to do useful work (by reference)
  47          */
  48         public function __construct( callable $condition, $timeout = 5.0, &$busyCallbacks = [] ) {
  49                 $this->condition = $condition;
  50                 $this->timeout = $timeout;
  51                 $this->busyCallbacks =& $busyCallbacks;
  52         }
  53
  54         /**
  55          * Invoke the loop and continue until either:
  56          *   - a) The condition callback does not return either CONDITION_CONTINUE or true
  57          *   - b) The timeout is reached
  58          * This a condition callback can return true (stop) or false (continue) for convenience.
  59          * In such cases, the halting result of "true" will be converted to CONDITION_REACHED.
  60          *
  61          * Exceptions in callbacks will be caught and the callback will be swapped with
  62          * one that simply rethrows that exception back to the caller when invoked.
  63          *
  64          * @return integer WaitConditionLoop::CONDITION_* constant
  65          * @throws Exception Any error from the condition callback
  66          */
  67         public function invoke() {
  68                 $elapsed = 0.0; // seconds
  69                 $sleepUs = 0; // microseconds to sleep each time
  70                 $lastCheck = false;
  71                 $finalResult = self::CONDITION_TIMED_OUT;
  72                 do {
  73                         $checkStartTime = $this->getWallTime();
  74                         // Check if the condition is met yet
  75                         $realStart = $this->getWallTime();
  76                         $cpuStart = $this->getCpuTime();
  77                         $checkResult = call_user_func( $this->condition );
  78                         $cpu = $this->getCpuTime() - $cpuStart;
  79                         $real = $this->getWallTime() - $realStart;
  80                         // Exit if the condition is reached
  81                         if ( (int)$checkResult !== self::CONDITION_CONTINUE ) {
  82                                 $finalResult = is_int( $checkResult ) ? $checkResult : self::CONDITION_REACHED;
  83                                 break;
  84                         } elseif ( $lastCheck ) {
  85                                 break; // timeout
  86                         }
  87                         // Detect if condition callback seems to block or if justs burns CPU
  88                         $conditionUsesInterrupts = ( $real > 0.100 && $cpu <= $real * .03 );
  89                         if ( !$this->popAndRunBusyCallback() && !$conditionUsesInterrupts ) {
  90                                 // 10 queries = 10(10+100)/2 ms = 550ms, 14 queries = 1050ms
  91                                 $sleepUs = min( $sleepUs + 10 * 1e3, 1e6 ); // stop incrementing at ~1s
  92                                 $this->usleep( $sleepUs );
  93                         }
  94                         $checkEndTime = $this->getWallTime();
  95                         // The max() protects against the clock getting set back
  96                         $elapsed += max( $checkEndTime - $checkStartTime, 0.010 );
  97                         // Do not let slow callbacks timeout without checking the condition one more time
  98                         $lastCheck = ( $elapsed >= $this->timeout );
  99                 } while ( true );
 100
 101                 $this->lastWaitTime = $elapsed;
 102
 103                 return $finalResult;
 104         }
 105
 106         /**
 107          * @return float Seconds
 108          */
 109         public function getLastWaitTime() {
 110                 return $this->lastWaitTime;
 111         }
 112
 113         /**
 114          * @param integer $microseconds
 115          */
 116         protected function usleep( $microseconds ) {
 117                 usleep( $microseconds );
 118         }
 119
 120         /**
 121          * @return float
 122          */
 123         protected function getWallTime() {
 124                 return microtime( true );
 125         }
 126
 127         /**
 128          * @return float Returns 0.0 if not supported (Windows on PHP < 7)
 129          */
 130         protected function getCpuTime() {
 131                 $time = 0.0;
 132
 133                 if ( defined( 'HHVM_VERSION' ) && PHP_OS === 'Linux' ) {
 134                         $ru = getrusage( 2 /* RUSAGE_THREAD */ );
 135                 } else {
 136                         $ru = getrusage( 0 /* RUSAGE_SELF */ );
 137                 }
 138                 if ( $ru ) {
 139                         $time += $ru['ru_utime.tv_sec'] + $ru['ru_utime.tv_usec'] / 1e6;
 140                         $time += $ru['ru_stime.tv_sec'] + $ru['ru_stime.tv_usec'] / 1e6;
 141                 }
 142
 143                 return $time;
 144         }
 145
 146         /**
 147          * Run one of the callbacks that does work ahead of time for another caller
 148          *
 149          * @return bool Whether a callback was executed
 150          */
 151         private function popAndRunBusyCallback() {
 152                 if ( $this->busyCallbacks ) {
 153                         reset( $this->busyCallbacks );
 154                         $key = key( $this->busyCallbacks );
 155                         /** @var callable $workCallback */
 156                         $workCallback =& $this->busyCallbacks[$key];
 157                         try {
 158                                 $workCallback();
 159                         } catch ( Exception $e ) {
 160                                 $workCallback = function () use ( $e ) {
 161                                         throw $e;
 162                                 };
 163                         }
 164                         unset( $this->busyCallbacks[$key] ); // consume
 165
 166                         return true;
 167                 }
 168
 169                 return false;
 170         }
 171 }