vendor/wikimedia/wait-condition-loop/src/WaitConditionLoop.php

   1 <?php
   2 /**
   3  * Wait loop that reaches a condition or times out.
   4  *
   5  * Copyright (C) 2016 Aaron Schulz <aschulz@wikimedia.org>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License along
  18  * with this program; if not, write to the Free Software Foundation, Inc.,
  19  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  20  * http://www.gnu.org/copyleft/gpl.html
  21  *
  22  * @file
  23  * @author Aaron Schulz
  24  */
  25
  26 namespace Wikimedia;
  27
  28 /**
  29  * Wait loop that reaches a condition or times out
  30  */
  31 class WaitConditionLoop {
  32         /** @var callable */
  33         private $condition;
  34         /** @var callable[] */
  35         private $busyCallbacks = [];
  36         /** @var float Seconds */
  37         private $timeout;
  38         /** @var float Seconds */
  39         private $lastWaitTime;
  40         /** @var integer|null */
  41         private $rusageMode;
  42
  43         const CONDITION_REACHED = 1;
  44         const CONDITION_CONTINUE = 0; // evaluates as falsey
  45         const CONDITION_FAILED = -1;
  46         const CONDITION_TIMED_OUT = -2;
  47         const CONDITION_ABORTED = -3;
  48
  49         /**
  50          * @param callable $condition Callback that returns a WaitConditionLoop::CONDITION_ constant
  51          * @param float $timeout Timeout in seconds
  52          * @param array &$busyCallbacks List of callbacks to do useful work (by reference)
  53          */
  54         public function __construct( callable $condition, $timeout = 5.0, &$busyCallbacks = [] ) {
  55                 $this->condition = $condition;
  56                 $this->timeout = $timeout;
  57                 $this->busyCallbacks =& $busyCallbacks;
  58
  59                 if ( defined( 'HHVM_VERSION' ) && PHP_OS === 'Linux' ) {
  60                         $this->rusageMode = 2; // RUSAGE_THREAD
  61                 } elseif ( function_exists( 'getrusage' ) ) {
  62                         $this->rusageMode = 0; // RUSAGE_SELF
  63                 }
  64         }
  65
  66         /**
  67          * Invoke the loop and continue until either:
  68          *   - a) The condition callback returns neither CONDITION_CONTINUE nor false
  69          *   - b) The timeout is reached
  70          * This a condition callback can return true (stop) or false (continue) for convenience.
  71          * In such cases, the halting result of "true" will be converted to CONDITION_REACHED.
  72          *
  73          * If $timeout is 0, then only the condition callback will be called (no busy callbacks),
  74          * and this will immediately return CONDITION_FAILED if the condition was not met.
  75          *
  76          * Exceptions in callbacks will be caught and the callback will be swapped with
  77          * one that simply rethrows that exception back to the caller when invoked.
  78          *
  79          * @return integer WaitConditionLoop::CONDITION_* constant
  80          * @throws \Exception Any error from the condition callback
  81          */
  82         public function invoke() {
  83                 $elapsed = 0.0; // seconds
  84                 $sleepUs = 0; // microseconds to sleep each time
  85                 $lastCheck = false;
  86                 $finalResult = self::CONDITION_TIMED_OUT;
  87                 do {
  88                         $checkStartTime = $this->getWallTime();
  89                         // Check if the condition is met yet
  90                         $realStart = $this->getWallTime();
  91                         $cpuStart = $this->getCpuTime();
  92                         $checkResult = call_user_func( $this->condition );
  93                         $cpu = $this->getCpuTime() - $cpuStart;
  94                         $real = $this->getWallTime() - $realStart;
  95                         // Exit if the condition is reached, an error occurs, or this is non-blocking
  96                         if ( $this->timeout <= 0 ) {
  97                                 $finalResult = $checkResult ? self::CONDITION_REACHED : self::CONDITION_FAILED;
  98                                 break;
  99                         } elseif ( (int)$checkResult !== self::CONDITION_CONTINUE ) {
 100                                 if ( is_int( $checkResult ) ) {
 101                                         $finalResult = $checkResult;
 102                                 } else {
 103                                         $finalResult = self::CONDITION_REACHED;
 104                                 }
 105                                 break;
 106                         } elseif ( $lastCheck ) {
 107                                 break; // timeout reached
 108                         }
 109                         // Detect if condition callback seems to block or if justs burns CPU
 110                         $conditionUsesInterrupts = ( $real > 0.100 && $cpu <= $real * .03 );
 111                         if ( !$this->popAndRunBusyCallback() && !$conditionUsesInterrupts ) {
 112                                 // 10 queries = 10(10+100)/2 ms = 550ms, 14 queries = 1050ms
 113                                 $sleepUs = min( $sleepUs + 10 * 1e3, 1e6 ); // stop incrementing at ~1s
 114                                 $this->usleep( $sleepUs );
 115                         }
 116                         $checkEndTime = $this->getWallTime();
 117                         // The max() protects against the clock getting set back
 118                         $elapsed += max( $checkEndTime - $checkStartTime, 0.010 );
 119                         // Do not let slow callbacks timeout without checking the condition one more time
 120                         $lastCheck = ( $elapsed >= $this->timeout );
 121                 } while ( true );
 122
 123                 $this->lastWaitTime = $elapsed;
 124
 125                 return $finalResult;
 126         }
 127
 128         /**
 129          * @return float Seconds
 130          */
 131         public function getLastWaitTime() {
 132                 return $this->lastWaitTime;
 133         }
 134
 135         /**
 136          * @param integer $microseconds
 137          */
 138         protected function usleep( $microseconds ) {
 139                 usleep( $microseconds );
 140         }
 141
 142         /**
 143          * @return float
 144          */
 145         protected function getWallTime() {
 146                 return microtime( true );
 147         }
 148
 149         /**
 150          * @return float Returns 0.0 if not supported (Windows on PHP < 7)
 151          */
 152         protected function getCpuTime() {
 153                 if ( $this->rusageMode === null ) {
 154                         return microtime( true ); // assume worst case (all time is CPU)
 155                 }
 156
 157                 $ru = getrusage( $this->rusageMode );
 158                 $time = $ru['ru_utime.tv_sec'] + $ru['ru_utime.tv_usec'] / 1e6;
 159                 $time += $ru['ru_stime.tv_sec'] + $ru['ru_stime.tv_usec'] / 1e6;
 160
 161                 return $time;
 162         }
 163
 164         /**
 165          * Run one of the callbacks that does work ahead of time for another caller
 166          *
 167          * @return bool Whether a callback was executed
 168          */
 169         private function popAndRunBusyCallback() {
 170                 if ( $this->busyCallbacks ) {
 171                         reset( $this->busyCallbacks );
 172                         $key = key( $this->busyCallbacks );
 173                         /** @var callable $workCallback */
 174                         $workCallback =& $this->busyCallbacks[$key];
 175                         try {
 176                                 $workCallback();
 177                         } catch ( \Exception $e ) {
 178                                 $workCallback = function () use ( $e ) {
 179                                         throw $e;
 180                                 };
 181                         }
 182                         unset( $this->busyCallbacks[$key] ); // consume
 183
 184                         return true;
 185                 }
 186
 187                 return false;
 188         }
 189 }