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         /** @var integer|null */
  38         private $rusageMode;
  39
  40         const CONDITION_REACHED = 1;
  41         const CONDITION_CONTINUE = 0; // evaluates as falsey
  42         const CONDITION_FAILED = -1;
  43         const CONDITION_TIMED_OUT = -2;
  44         const CONDITION_ABORTED = -3;
  45
  46         /**
  47          * @param callable $condition Callback that returns a WaitConditionLoop::CONDITION_ constant
  48          * @param float $timeout Timeout in seconds
  49          * @param array &$busyCallbacks List of callbacks to do useful work (by reference)
  50          */
  51         public function __construct( callable $condition, $timeout = 5.0, &$busyCallbacks = [] ) {
  52                 $this->condition = $condition;
  53                 $this->timeout = $timeout;
  54                 $this->busyCallbacks =& $busyCallbacks;
  55
  56                 if ( defined( 'HHVM_VERSION' ) && PHP_OS === 'Linux' ) {
  57                         $this->rusageMode = 2; // RUSAGE_THREAD
  58                 } elseif ( function_exists( 'getrusage' ) ) {
  59                         $this->rusageMode = 0; // RUSAGE_SELF
  60                 }
  61         }
  62
  63         /**
  64          * Invoke the loop and continue until either:
  65          *   - a) The condition callback returns neither CONDITION_CONTINUE nor false
  66          *   - b) The timeout is reached
  67          * This a condition callback can return true (stop) or false (continue) for convenience.
  68          * In such cases, the halting result of "true" will be converted to CONDITION_REACHED.
  69          *
  70          * If $timeout is 0, then only the condition callback will be called (no busy callbacks),
  71          * and this will immediately return CONDITION_FAILED if the condition was not met.
  72          *
  73          * Exceptions in callbacks will be caught and the callback will be swapped with
  74          * one that simply rethrows that exception back to the caller when invoked.
  75          *
  76          * @return integer WaitConditionLoop::CONDITION_* constant
  77          * @throws Exception Any error from the condition callback
  78          */
  79         public function invoke() {
  80                 $elapsed = 0.0; // seconds
  81                 $sleepUs = 0; // microseconds to sleep each time
  82                 $lastCheck = false;
  83                 $finalResult = self::CONDITION_TIMED_OUT;
  84                 do {
  85                         $checkStartTime = $this->getWallTime();
  86                         // Check if the condition is met yet
  87                         $realStart = $this->getWallTime();
  88                         $cpuStart = $this->getCpuTime();
  89                         $checkResult = call_user_func( $this->condition );
  90                         $cpu = $this->getCpuTime() - $cpuStart;
  91                         $real = $this->getWallTime() - $realStart;
  92                         // Exit if the condition is reached, and error occurs, or this is non-blocking
  93                         if ( $this->timeout <= 0 ) {
  94                                 $finalResult = $checkResult ? self::CONDITION_REACHED : self::CONDITION_FAILED;
  95                                 break;
  96                         } elseif ( (int)$checkResult !== self::CONDITION_CONTINUE ) {
  97                                 if ( is_int( $checkResult ) ) {
  98                                         $finalResult = $checkResult;
  99                                 } else {
 100                                         $finalResult = self::CONDITION_REACHED;
 101                                 }
 102                                 break;
 103                         } elseif ( $lastCheck ) {
 104                                 break; // timeout reached
 105                         }
 106                         // Detect if condition callback seems to block or if justs burns CPU
 107                         $conditionUsesInterrupts = ( $real > 0.100 && $cpu <= $real * .03 );
 108                         if ( !$this->popAndRunBusyCallback() && !$conditionUsesInterrupts ) {
 109                                 // 10 queries = 10(10+100)/2 ms = 550ms, 14 queries = 1050ms
 110                                 $sleepUs = min( $sleepUs + 10 * 1e3, 1e6 ); // stop incrementing at ~1s
 111                                 $this->usleep( $sleepUs );
 112                         }
 113                         $checkEndTime = $this->getWallTime();
 114                         // The max() protects against the clock getting set back
 115                         $elapsed += max( $checkEndTime - $checkStartTime, 0.010 );
 116                         // Do not let slow callbacks timeout without checking the condition one more time
 117                         $lastCheck = ( $elapsed >= $this->timeout );
 118                 } while ( true );
 119
 120                 $this->lastWaitTime = $elapsed;
 121
 122                 return $finalResult;
 123         }
 124
 125         /**
 126          * @return float Seconds
 127          */
 128         public function getLastWaitTime() {
 129                 return $this->lastWaitTime;
 130         }
 131
 132         /**
 133          * @param integer $microseconds
 134          */
 135         protected function usleep( $microseconds ) {
 136                 usleep( $microseconds );
 137         }
 138
 139         /**
 140          * @return float
 141          */
 142         protected function getWallTime() {
 143                 return microtime( true );
 144         }
 145
 146         /**
 147          * @return float Returns 0.0 if not supported (Windows on PHP < 7)
 148          */
 149         protected function getCpuTime() {
 150                 if ( $this->rusageMode === null ) {
 151                         return microtime( true ); // assume worst case (all time is CPU)
 152                 }
 153
 154                 $ru = getrusage( $this->rusageMode );
 155                 $time = $ru['ru_utime.tv_sec'] + $ru['ru_utime.tv_usec'] / 1e6;
 156                 $time += $ru['ru_stime.tv_sec'] + $ru['ru_stime.tv_usec'] / 1e6;
 157
 158                 return $time;
 159         }
 160
 161         /**
 162          * Run one of the callbacks that does work ahead of time for another caller
 163          *
 164          * @return bool Whether a callback was executed
 165          */
 166         private function popAndRunBusyCallback() {
 167                 if ( $this->busyCallbacks ) {
 168                         reset( $this->busyCallbacks );
 169                         $key = key( $this->busyCallbacks );
 170                         /** @var callable $workCallback */
 171                         $workCallback =& $this->busyCallbacks[$key];
 172                         try {
 173                                 $workCallback();
 174                         } catch ( Exception $e ) {
 175                                 $workCallback = function () use ( $e ) {
 176                                         throw $e;
 177                                 };
 178                         }
 179                         unset( $this->busyCallbacks[$key] ); // consume
 180
 181                         return true;
 182                 }
 183
 184                 return false;
 185         }
 186 }