includes/utils/UIDGenerator.php

   1 <?php
   2 /**
   3  * This file deals with UID generation.
   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  */
  22 use Wikimedia\Assert\Assert;
  23 use MediaWiki\MediaWikiServices;
  24
  25 /**
  26  * Class for getting statistically unique IDs
  27  *
  28  * @since 1.21
  29  */
  30 class UIDGenerator {
  31         /** @var UIDGenerator */
  32         protected static $instance = null;
  33
  34         protected $nodeIdFile; // string; local file path
  35         protected $nodeId32; // string; node ID in binary (32 bits)
  36         protected $nodeId48; // string; node ID in binary (48 bits)
  37
  38         protected $lockFile88; // string; local file path
  39         protected $lockFile128; // string; local file path
  40         protected $lockFileUUID; // string; local file path
  41
  42         /** @var array */
  43         protected $fileHandles = []; // cache file handles
  44
  45         const QUICK_RAND = 1; // get randomness from fast and insecure sources
  46         const QUICK_VOLATILE = 2; // use an APC like in-memory counter if available
  47
  48         protected function __construct() {
  49                 $this->nodeIdFile = wfTempDir() . '/mw-' . __CLASS__ . '-UID-nodeid';
  50                 $nodeId = '';
  51                 if ( is_file( $this->nodeIdFile ) ) {
  52                         $nodeId = file_get_contents( $this->nodeIdFile );
  53                 }
  54                 // Try to get some ID that uniquely identifies this machine (RFC 4122)...
  55                 if ( !preg_match( '/^[0-9a-f]{12}$/i', $nodeId ) ) {
  56                         Wikimedia\suppressWarnings();
  57                         if ( wfIsWindows() ) {
  58                                 // https://technet.microsoft.com/en-us/library/bb490913.aspx
  59                                 $csv = trim( wfShellExec( 'getmac /NH /FO CSV' ) );
  60                                 $line = substr( $csv, 0, strcspn( $csv, "\n" ) );
  61                                 $info = str_getcsv( $line );
  62                                 $nodeId = isset( $info[0] ) ? str_replace( '-', '', $info[0] ) : '';
  63                         } elseif ( is_executable( '/sbin/ifconfig' ) ) { // Linux/BSD/Solaris/OS X
  64                                 // See https://linux.die.net/man/8/ifconfig
  65                                 $m = [];
  66                                 preg_match( '/\s([0-9a-f]{2}(:[0-9a-f]{2}){5})\s/',
  67                                         wfShellExec( '/sbin/ifconfig -a' ), $m );
  68                                 $nodeId = isset( $m[1] ) ? str_replace( ':', '', $m[1] ) : '';
  69                         }
  70                         Wikimedia\restoreWarnings();
  71                         if ( !preg_match( '/^[0-9a-f]{12}$/i', $nodeId ) ) {
  72                                 $nodeId = MWCryptRand::generateHex( 12, true );
  73                                 $nodeId[1] = dechex( hexdec( $nodeId[1] ) | 0x1 ); // set multicast bit
  74                         }
  75                         file_put_contents( $this->nodeIdFile, $nodeId ); // cache
  76                 }
  77                 $this->nodeId32 = Wikimedia\base_convert( substr( sha1( $nodeId ), 0, 8 ), 16, 2, 32 );
  78                 $this->nodeId48 = Wikimedia\base_convert( $nodeId, 16, 2, 48 );
  79                 // If different processes run as different users, they may have different temp dirs.
  80                 // This is dealt with by initializing the clock sequence number and counters randomly.
  81                 $this->lockFile88 = wfTempDir() . '/mw-' . __CLASS__ . '-UID-88';
  82                 $this->lockFile128 = wfTempDir() . '/mw-' . __CLASS__ . '-UID-128';
  83                 $this->lockFileUUID = wfTempDir() . '/mw-' . __CLASS__ . '-UUID-128';
  84         }
  85
  86         /**
  87          * @todo move to MW-specific factory class and inject temp dir
  88          * @return UIDGenerator
  89          */
  90         protected static function singleton() {
  91                 if ( self::$instance === null ) {
  92                         self::$instance = new self();
  93                 }
  94
  95                 return self::$instance;
  96         }
  97
  98         /**
  99          * Get a statistically unique 88-bit unsigned integer ID string.
 100          * The bits of the UID are prefixed with the time (down to the millisecond).
 101          *
 102          * These IDs are suitable as values for the shard key of distributed data.
 103          * If a column uses these as values, it should be declared UNIQUE to handle collisions.
 104          * New rows almost always have higher UIDs, which makes B-TREE updates on INSERT fast.
 105          * They can also be stored "DECIMAL(27) UNSIGNED" or BINARY(11) in MySQL.
 106          *
 107          * UID generation is serialized on each server (as the node ID is for the whole machine).
 108          *
 109          * @param int $base Specifies a base other than 10
 110          * @return string Number
 111          * @throws RuntimeException
 112          */
 113         public static function newTimestampedUID88( $base = 10 ) {
 114                 Assert::parameterType( 'integer', $base, '$base' );
 115                 Assert::parameter( $base <= 36, '$base', 'must be <= 36' );
 116                 Assert::parameter( $base >= 2, '$base', 'must be >= 2' );
 117
 118                 $gen = self::singleton();
 119                 $info = $gen->getTimeAndDelay( 'lockFile88', 1, 1024, 1024 );
 120                 $info['offsetCounter'] = $info['offsetCounter'] % 1024;
 121                 return Wikimedia\base_convert( $gen->getTimestampedID88( $info ), 2, $base );
 122         }
 123
 124         /**
 125          * @param array $info result of UIDGenerator::getTimeAndDelay(), or
 126          *  for sub classes, a seqencial array like (time, offsetCounter).
 127          * @return string 88 bits
 128          * @throws RuntimeException
 129          */
 130         protected function getTimestampedID88( array $info ) {
 131                 if ( isset( $info['time'] ) ) {
 132                         $time = $info['time'];
 133                         $counter = $info['offsetCounter'];
 134                 } else {
 135                         $time = $info[0];
 136                         $counter = $info[1];
 137                 }
 138                 // Take the 46 LSBs of "milliseconds since epoch"
 139                 $id_bin = $this->millisecondsSinceEpochBinary( $time );
 140                 // Add a 10 bit counter resulting in 56 bits total
 141                 $id_bin .= str_pad( decbin( $counter ), 10, '0', STR_PAD_LEFT );
 142                 // Add the 32 bit node ID resulting in 88 bits total
 143                 $id_bin .= $this->nodeId32;
 144                 // Convert to a 1-27 digit integer string
 145                 if ( strlen( $id_bin ) !== 88 ) {
 146                         throw new RuntimeException( "Detected overflow for millisecond timestamp." );
 147                 }
 148
 149                 return $id_bin;
 150         }
 151
 152         /**
 153          * Get a statistically unique 128-bit unsigned integer ID string.
 154          * The bits of the UID are prefixed with the time (down to the millisecond).
 155          *
 156          * These IDs are suitable as globally unique IDs, without any enforced uniqueness.
 157          * New rows almost always have higher UIDs, which makes B-TREE updates on INSERT fast.
 158          * They can also be stored as "DECIMAL(39) UNSIGNED" or BINARY(16) in MySQL.
 159          *
 160          * UID generation is serialized on each server (as the node ID is for the whole machine).
 161          *
 162          * @param int $base Specifies a base other than 10
 163          * @return string Number
 164          * @throws RuntimeException
 165          */
 166         public static function newTimestampedUID128( $base = 10 ) {
 167                 Assert::parameterType( 'integer', $base, '$base' );
 168                 Assert::parameter( $base <= 36, '$base', 'must be <= 36' );
 169                 Assert::parameter( $base >= 2, '$base', 'must be >= 2' );
 170
 171                 $gen = self::singleton();
 172                 $info = $gen->getTimeAndDelay( 'lockFile128', 16384, 1048576, 1048576 );
 173                 $info['offsetCounter'] = $info['offsetCounter'] % 1048576;
 174
 175                 return Wikimedia\base_convert( $gen->getTimestampedID128( $info ), 2, $base );
 176         }
 177
 178         /**
 179          * @param array $info The result of UIDGenerator::getTimeAndDelay(),
 180          *  for sub classes, a seqencial array like (time, offsetCounter, clkSeq).
 181          * @return string 128 bits
 182          * @throws RuntimeException
 183          */
 184         protected function getTimestampedID128( array $info ) {
 185                 if ( isset( $info['time'] ) ) {
 186                         $time = $info['time'];
 187                         $counter = $info['offsetCounter'];
 188                         $clkSeq = $info['clkSeq'];
 189                 } else {
 190                         $time = $info[0];
 191                         $counter = $info[1];
 192                         $clkSeq = $info[2];
 193                 }
 194                 // Take the 46 LSBs of "milliseconds since epoch"
 195                 $id_bin = $this->millisecondsSinceEpochBinary( $time );
 196                 // Add a 20 bit counter resulting in 66 bits total
 197                 $id_bin .= str_pad( decbin( $counter ), 20, '0', STR_PAD_LEFT );
 198                 // Add a 14 bit clock sequence number resulting in 80 bits total
 199                 $id_bin .= str_pad( decbin( $clkSeq ), 14, '0', STR_PAD_LEFT );
 200                 // Add the 48 bit node ID resulting in 128 bits total
 201                 $id_bin .= $this->nodeId48;
 202                 // Convert to a 1-39 digit integer string
 203                 if ( strlen( $id_bin ) !== 128 ) {
 204                         throw new RuntimeException( "Detected overflow for millisecond timestamp." );
 205                 }
 206
 207                 return $id_bin;
 208         }
 209
 210         /**
 211          * Return an RFC4122 compliant v1 UUID
 212          *
 213          * @return string
 214          * @throws RuntimeException
 215          * @since 1.27
 216          */
 217         public static function newUUIDv1() {
 218                 $gen = self::singleton();
 219                 // There can be up to 10000 intervals for the same millisecond timestamp.
 220                 // [0,4999] counter + [0,5000] offset is in [0,9999] for the offset counter.
 221                 // Add this onto the timestamp to allow making up to 5000 IDs per second.
 222                 return $gen->getUUIDv1( $gen->getTimeAndDelay( 'lockFileUUID', 16384, 5000, 5001 ) );
 223         }
 224
 225         /**
 226          * Return an RFC4122 compliant v1 UUID
 227          *
 228          * @return string 32 hex characters with no hyphens
 229          * @throws RuntimeException
 230          * @since 1.27
 231          */
 232         public static function newRawUUIDv1() {
 233                 return str_replace( '-', '', self::newUUIDv1() );
 234         }
 235
 236         /**
 237          * @param array $info Result of UIDGenerator::getTimeAndDelay()
 238          * @return string 128 bits
 239          */
 240         protected function getUUIDv1( array $info ) {
 241                 $clkSeq_bin = Wikimedia\base_convert( $info['clkSeq'], 10, 2, 14 );
 242                 $time_bin = $this->intervalsSinceGregorianBinary( $info['time'], $info['offsetCounter'] );
 243                 // Take the 32 bits of "time low"
 244                 $id_bin = substr( $time_bin, 28, 32 );
 245                 // Add 16 bits of "time mid" resulting in 48 bits total
 246                 $id_bin .= substr( $time_bin, 12, 16 );
 247                 // Add 4 bit version resulting in 52 bits total
 248                 $id_bin .= '0001';
 249                 // Add 12 bits of "time high" resulting in 64 bits total
 250                 $id_bin .= substr( $time_bin, 0, 12 );
 251                 // Add 2 bits of "variant" resulting in 66 bits total
 252                 $id_bin .= '10';
 253                 // Add 6 bits of "clock seq high" resulting in 72 bits total
 254                 $id_bin .= substr( $clkSeq_bin, 0, 6 );
 255                 // Add 8 bits of "clock seq low" resulting in 80 bits total
 256                 $id_bin .= substr( $clkSeq_bin, 6, 8 );
 257                 // Add the 48 bit node ID resulting in 128 bits total
 258                 $id_bin .= $this->nodeId48;
 259                 // Convert to a 32 char hex string with dashes
 260                 if ( strlen( $id_bin ) !== 128 ) {
 261                         throw new RuntimeException( "Detected overflow for millisecond timestamp." );
 262                 }
 263                 $hex = Wikimedia\base_convert( $id_bin, 2, 16, 32 );
 264                 return sprintf( '%s-%s-%s-%s-%s',
 265                         // "time_low" (32 bits)
 266                         substr( $hex, 0, 8 ),
 267                         // "time_mid" (16 bits)
 268                         substr( $hex, 8, 4 ),
 269                         // "time_hi_and_version" (16 bits)
 270                         substr( $hex, 12, 4 ),
 271                         // "clk_seq_hi_res" (8 bits) and "clk_seq_low" (8 bits)
 272                         substr( $hex, 16, 4 ),
 273                         // "node" (48 bits)
 274                         substr( $hex, 20, 12 )
 275                 );
 276         }
 277
 278         /**
 279          * Return an RFC4122 compliant v4 UUID
 280          *
 281          * @param int $flags Bitfield (supports UIDGenerator::QUICK_RAND)
 282          * @return string
 283          * @throws RuntimeException
 284          */
 285         public static function newUUIDv4( $flags = 0 ) {
 286                 $hex = ( $flags & self::QUICK_RAND )
 287                         ? wfRandomString( 31 )
 288                         : MWCryptRand::generateHex( 31 );
 289
 290                 return sprintf( '%s-%s-%s-%s-%s',
 291                         // "time_low" (32 bits)
 292                         substr( $hex, 0, 8 ),
 293                         // "time_mid" (16 bits)
 294                         substr( $hex, 8, 4 ),
 295                         // "time_hi_and_version" (16 bits)
 296                         '4' . substr( $hex, 12, 3 ),
 297                         // "clk_seq_hi_res" (8 bits, variant is binary 10x) and "clk_seq_low" (8 bits)
 298                         dechex( 0x8 | ( hexdec( $hex[15] ) & 0x3 ) ) . $hex[16] . substr( $hex, 17, 2 ),
 299                         // "node" (48 bits)
 300                         substr( $hex, 19, 12 )
 301                 );
 302         }
 303
 304         /**
 305          * Return an RFC4122 compliant v4 UUID
 306          *
 307          * @param int $flags Bitfield (supports UIDGenerator::QUICK_RAND)
 308          * @return string 32 hex characters with no hyphens
 309          * @throws RuntimeException
 310          */
 311         public static function newRawUUIDv4( $flags = 0 ) {
 312                 return str_replace( '-', '', self::newUUIDv4( $flags ) );
 313         }
 314
 315         /**
 316          * Return an ID that is sequential *only* for this node and bucket
 317          *
 318          * These IDs are suitable for per-host sequence numbers, e.g. for some packet protocols.
 319          * If UIDGenerator::QUICK_VOLATILE is used the counter might reset on server restart.
 320          *
 321          * @param string $bucket Arbitrary bucket name (should be ASCII)
 322          * @param int $bits Bit size (<=48) of resulting numbers before wrap-around
 323          * @param int $flags (supports UIDGenerator::QUICK_VOLATILE)
 324          * @return float Integer value as float
 325          * @since 1.23
 326          */
 327         public static function newSequentialPerNodeID( $bucket, $bits = 48, $flags = 0 ) {
 328                 return current( self::newSequentialPerNodeIDs( $bucket, $bits, 1, $flags ) );
 329         }
 330
 331         /**
 332          * Return IDs that are sequential *only* for this node and bucket
 333          *
 334          * @see UIDGenerator::newSequentialPerNodeID()
 335          * @param string $bucket Arbitrary bucket name (should be ASCII)
 336          * @param int $bits Bit size (16 to 48) of resulting numbers before wrap-around
 337          * @param int $count Number of IDs to return
 338          * @param int $flags (supports UIDGenerator::QUICK_VOLATILE)
 339          * @return array Ordered list of float integer values
 340          * @since 1.23
 341          */
 342         public static function newSequentialPerNodeIDs( $bucket, $bits, $count, $flags = 0 ) {
 343                 $gen = self::singleton();
 344                 return $gen->getSequentialPerNodeIDs( $bucket, $bits, $count, $flags );
 345         }
 346
 347         /**
 348          * Return IDs that are sequential *only* for this node and bucket
 349          *
 350          * @see UIDGenerator::newSequentialPerNodeID()
 351          * @param string $bucket Arbitrary bucket name (should be ASCII)
 352          * @param int $bits Bit size (16 to 48) of resulting numbers before wrap-around
 353          * @param int $count Number of IDs to return
 354          * @param int $flags (supports UIDGenerator::QUICK_VOLATILE)
 355          * @return array Ordered list of float integer values
 356          * @throws RuntimeException
 357          */
 358         protected function getSequentialPerNodeIDs( $bucket, $bits, $count, $flags ) {
 359                 if ( $count <= 0 ) {
 360                         return []; // nothing to do
 361                 }
 362                 if ( $bits < 16 || $bits > 48 ) {
 363                         throw new RuntimeException( "Requested bit size ($bits) is out of range." );
 364                 }
 365
 366                 $counter = null; // post-increment persistent counter value
 367
 368                 // Use APC/etc if requested, available, and not in CLI mode;
 369                 // Counter values would not survive across script instances in CLI mode.
 370                 $cache = null;
 371                 if ( ( $flags & self::QUICK_VOLATILE ) && !wfIsCLI() ) {
 372                         $cache = MediaWikiServices::getInstance()->getLocalServerObjectCache();
 373                 }
 374                 if ( $cache ) {
 375                         $counter = $cache->incrWithInit( $bucket, $cache::TTL_INDEFINITE, $count, $count );
 376                         if ( $counter === false ) {
 377                                 throw new RuntimeException( 'Unable to set value to ' . get_class( $cache ) );
 378                         }
 379                 }
 380
 381                 // Note: use of fmod() avoids "division by zero" on 32 bit machines
 382                 if ( $counter === null ) {
 383                         $path = wfTempDir() . '/mw-' . __CLASS__ . '-' . rawurlencode( $bucket ) . '-48';
 384                         // Get the UID lock file handle
 385                         if ( isset( $this->fileHandles[$path] ) ) {
 386                                 $handle = $this->fileHandles[$path];
 387                         } else {
 388                                 $handle = fopen( $path, 'cb+' );
 389                                 $this->fileHandles[$path] = $handle ?: null; // cache
 390                         }
 391                         // Acquire the UID lock file
 392                         if ( $handle === false ) {
 393                                 throw new RuntimeException( "Could not open '{$path}'." );
 394                         }
 395                         if ( !flock( $handle, LOCK_EX ) ) {
 396                                 fclose( $handle );
 397                                 throw new RuntimeException( "Could not acquire '{$path}'." );
 398                         }
 399                         // Fetch the counter value and increment it...
 400                         rewind( $handle );
 401                         $counter = floor( trim( fgets( $handle ) ) ) + $count; // fetch as float
 402                         // Write back the new counter value
 403                         ftruncate( $handle, 0 );
 404                         rewind( $handle );
 405                         fwrite( $handle, fmod( $counter, 2 ** 48 ) ); // warp-around as needed
 406                         fflush( $handle );
 407                         // Release the UID lock file
 408                         flock( $handle, LOCK_UN );
 409                 }
 410
 411                 $ids = [];
 412                 $divisor = 2 ** $bits;
 413                 $currentId = floor( $counter - $count ); // pre-increment counter value
 414                 for ( $i = 0; $i < $count; ++$i ) {
 415                         $ids[] = fmod( ++$currentId, $divisor );
 416                 }
 417
 418                 return $ids;
 419         }
 420
 421         /**
 422          * Get a (time,counter,clock sequence) where (time,counter) is higher
 423          * than any previous (time,counter) value for the given clock sequence.
 424          * This is useful for making UIDs sequential on a per-node bases.
 425          *
 426          * @param string $lockFile Name of a local lock file
 427          * @param int $clockSeqSize The number of possible clock sequence values
 428          * @param int $counterSize The number of possible counter values
 429          * @param int $offsetSize The number of possible offset values
 430          * @return array Array with the following keys:
 431          *  - array 'time': array of seconds int and milliseconds int.
 432          *  - int 'counter'.
 433          *  - int 'clkSeq'.
 434          *  - int 'offset': .
 435          *  - int 'offsetCounter'.
 436          * @throws RuntimeException
 437          */
 438         protected function getTimeAndDelay( $lockFile, $clockSeqSize, $counterSize, $offsetSize ) {
 439                 // Get the UID lock file handle
 440                 if ( isset( $this->fileHandles[$lockFile] ) ) {
 441                         $handle = $this->fileHandles[$lockFile];
 442                 } else {
 443                         $handle = fopen( $this->$lockFile, 'cb+' );
 444                         $this->fileHandles[$lockFile] = $handle ?: null; // cache
 445                 }
 446                 // Acquire the UID lock file
 447                 if ( $handle === false ) {
 448                         throw new RuntimeException( "Could not open '{$this->$lockFile}'." );
 449                 }
 450                 if ( !flock( $handle, LOCK_EX ) ) {
 451                         fclose( $handle );
 452                         throw new RuntimeException( "Could not acquire '{$this->$lockFile}'." );
 453                 }
 454
 455                 // The formatters that use this method expect a timestamp with millisecond
 456                 // precision and a counter upto a certain size. When more IDs than the counter
 457                 // size are generated during the same timestamp, an exception is thrown as we
 458                 // cannot increment further, because the formatted ID would not have enough
 459                 // bits to fit the counter.
 460                 //
 461                 // To orchestrate this between independant PHP processes on the same hosts,
 462                 // we must have a common sense of time so that we only have to maintain
 463                 // a single counter in a single lock file.
 464
 465                 rewind( $handle );
 466                 // Format of lock file contents:
 467                 // "<clk seq> <sec> <msec> <counter> <rand offset>"
 468                 $data = explode( ' ', fgets( $handle ) );
 469
 470                 // Did the clock get moved back significantly?
 471                 $clockChanged = false;
 472
 473                 if ( count( $data ) === 5 ) {
 474                         // The UID lock file was already initialized
 475                         $clkSeq = (int)$data[0] % $clockSeqSize;
 476                         $prevTime = [ (int)$data[1], (int)$data[2] ];
 477                         // Counter for UIDs with the same timestamp,
 478                         $counter = 0;
 479                         $randOffset = (int)$data[4] % $counterSize;
 480
 481                         // If the system clock moved backwards by an NTP sync,
 482                         // or if the last writer process had its clock drift ahead,
 483                         // Try to catch up if the gap is small, so that we can keep a single
 484                         // monotonic logic file.
 485                         $time = $this->timeWaitUntil( $prevTime );
 486                         if ( $time === false ) {
 487                                 // Timed out. Treat it as a new clock
 488                                 $clockChanged = true;
 489                                 $time = $this->millitime();
 490                         } elseif ( $time === $prevTime ) {
 491                                 // Sanity check, only keep remainder if a previous writer wrote
 492                                 // something here that we don't accept.
 493                                 $counter = (int)$data[3] % $counterSize;
 494                                 // Bump the counter if the time has not changed yet
 495                                 if ( ++$counter >= $counterSize ) {
 496                                         // More IDs generated with the same time than counterSize can accomodate
 497                                         flock( $handle, LOCK_UN );
 498                                         throw new RuntimeException( "Counter overflow for timestamp value." );
 499                                 }
 500                         }
 501                 } else {
 502                         // Initialize UID lock file information
 503                         $clkSeq = mt_rand( 0, $clockSeqSize - 1 );
 504                         $time = $this->millitime();
 505                         $counter = 0;
 506                         $randOffset = mt_rand( 0, $offsetSize - 1 );
 507                 }
 508                 // microtime() and gettimeofday() can drift from time() at least on Windows.
 509                 // The drift is immediate for processes running while the system clock changes.
 510                 // time() does not have this problem. See https://bugs.php.net/bug.php?id=42659.
 511                 $drift = time() - $time[0];
 512                 if ( abs( $drift ) >= 2 ) {
 513                         // We don't want processes using too high or low timestamps to avoid duplicate
 514                         // UIDs and clock sequence number churn. This process should just be restarted.
 515                         flock( $handle, LOCK_UN ); // abort
 516                         throw new RuntimeException( "Process clock is outdated or drifted ({$drift}s)." );
 517                 }
 518                 // If microtime() is synced and a clock change was detected, then the clock went back
 519                 if ( $clockChanged ) {
 520                         // Bump the clock sequence number and also randomize the extra offset,
 521                         // which is useful for UIDs that do not include the clock sequence number.
 522                         $clkSeq = ( $clkSeq + 1 ) % $clockSeqSize;
 523                         $randOffset = mt_rand( 0, $offsetSize - 1 );
 524                         trigger_error( "Clock was set back; sequence number incremented." );
 525                 }
 526
 527                 // Update and release the UID lock file
 528                 ftruncate( $handle, 0 );
 529                 rewind( $handle );
 530                 fwrite( $handle, "{$clkSeq} {$time[0]} {$time[1]} {$counter} {$randOffset}" );
 531                 fflush( $handle );
 532                 flock( $handle, LOCK_UN );
 533
 534                 return [
 535                         'time'          => $time,
 536                         'counter'       => $counter,
 537                         'clkSeq'        => $clkSeq,
 538                         'offset'        => $randOffset,
 539                         'offsetCounter' => $counter + $randOffset,
 540                 ];
 541         }
 542
 543         /**
 544          * Wait till the current timestamp reaches $time and return the current
 545          * timestamp. This returns false if it would have to wait more than 10ms.
 546          *
 547          * @param array $time Result of UIDGenerator::millitime()
 548          * @return array|bool UIDGenerator::millitime() result or false
 549          */
 550         protected function timeWaitUntil( array $time ) {
 551                 do {
 552                         $ct = $this->millitime();
 553                         if ( $ct >= $time ) { // https://secure.php.net/manual/en/language.operators.comparison.php
 554                                 return $ct; // current timestamp is higher than $time
 555                         }
 556                 } while ( ( ( $time[0] - $ct[0] ) * 1000 + ( $time[1] - $ct[1] ) ) <= 10 );
 557
 558                 return false;
 559         }
 560
 561         /**
 562          * @param array $time Result of UIDGenerator::millitime()
 563          * @return string 46 LSBs of "milliseconds since epoch" in binary (rolls over in 4201)
 564          * @throws RuntimeException
 565          */
 566         protected function millisecondsSinceEpochBinary( array $time ) {
 567                 list( $sec, $msec ) = $time;
 568                 $ts = 1000 * $sec + $msec;
 569                 if ( $ts > 2 ** 52 ) {
 570                         throw new RuntimeException( __METHOD__ .
 571                                 ': sorry, this function doesn\'t work after the year 144680' );
 572                 }
 573
 574                 return substr( Wikimedia\base_convert( $ts, 10, 2, 46 ), -46 );
 575         }
 576
 577         /**
 578          * @param array $time Result of UIDGenerator::millitime()
 579          * @param int $delta Number of intervals to add on to the timestamp
 580          * @return string 60 bits of "100ns intervals since 15 October 1582" (rolls over in 3400)
 581          * @throws RuntimeException
 582          */
 583         protected function intervalsSinceGregorianBinary( array $time, $delta = 0 ) {
 584                 list( $sec, $msec ) = $time;
 585                 $offset = '122192928000000000';
 586                 if ( PHP_INT_SIZE >= 8 ) { // 64 bit integers
 587                         $ts = ( 1000 * $sec + $msec ) * 10000 + (int)$offset + $delta;
 588                         $id_bin = str_pad( decbin( $ts % ( 2 ** 60 ) ), 60, '0', STR_PAD_LEFT );
 589                 } elseif ( extension_loaded( 'gmp' ) ) {
 590                         $ts = gmp_add( gmp_mul( (string)$sec, '1000' ), (string)$msec ); // ms
 591                         $ts = gmp_add( gmp_mul( $ts, '10000' ), $offset ); // 100ns intervals
 592                         $ts = gmp_add( $ts, (string)$delta );
 593                         $ts = gmp_mod( $ts, gmp_pow( '2', '60' ) ); // wrap around
 594                         $id_bin = str_pad( gmp_strval( $ts, 2 ), 60, '0', STR_PAD_LEFT );
 595                 } elseif ( extension_loaded( 'bcmath' ) ) {
 596                         $ts = bcadd( bcmul( $sec, 1000 ), $msec ); // ms
 597                         $ts = bcadd( bcmul( $ts, 10000 ), $offset ); // 100ns intervals
 598                         $ts = bcadd( $ts, $delta );
 599                         $ts = bcmod( $ts, bcpow( 2, 60 ) ); // wrap around
 600                         $id_bin = Wikimedia\base_convert( $ts, 10, 2, 60 );
 601                 } else {
 602                         throw new RuntimeException( 'bcmath or gmp extension required for 32 bit machines.' );
 603                 }
 604                 return $id_bin;
 605         }
 606
 607         /**
 608          * @return array (current time in seconds, milliseconds since then)
 609          */
 610         protected function millitime() {
 611                 list( $msec, $sec ) = explode( ' ', microtime() );
 612
 613                 return [ (int)$sec, (int)( $msec * 1000 ) ];
 614         }
 615
 616         /**
 617          * Delete all cache files that have been created.
 618          *
 619          * This is a cleanup method primarily meant to be used from unit tests to
 620          * avoid poluting the local filesystem. If used outside of a unit test
 621          * environment it should be used with caution as it may destroy state saved
 622          * in the files.
 623          *
 624          * @see unitTestTearDown
 625          * @since 1.23
 626          * @codeCoverageIgnore
 627          */
 628         private function deleteCacheFiles() {
 629                 // T46850
 630                 foreach ( $this->fileHandles as $path => $handle ) {
 631                         if ( $handle !== null ) {
 632                                 fclose( $handle );
 633                         }
 634                         if ( is_file( $path ) ) {
 635                                 unlink( $path );
 636                         }
 637                         unset( $this->fileHandles[$path] );
 638                 }
 639                 if ( is_file( $this->nodeIdFile ) ) {
 640                         unlink( $this->nodeIdFile );
 641                 }
 642         }
 643
 644         /**
 645          * Cleanup resources when tearing down after a unit test.
 646          *
 647          * This is a cleanup method primarily meant to be used from unit tests to
 648          * avoid poluting the local filesystem. If used outside of a unit test
 649          * environment it should be used with caution as it may destroy state saved
 650          * in the files.
 651          *
 652          * @internal For use by unit tests
 653          * @see deleteCacheFiles
 654          * @since 1.23
 655          * @codeCoverageIgnore
 656          */
 657         public static function unitTestTearDown() {
 658                 // T46850
 659                 $gen = self::singleton();
 660                 $gen->deleteCacheFiles();
 661         }
 662
 663         function __destruct() {
 664                 array_map( 'fclose', array_filter( $this->fileHandles ) );
 665         }
 666 }