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mediawiki/includes/utils/UIDGenerator.php
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UIDGenerator.php
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<?php
/**
* This file deals with UID generation.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
* http://www.gnu.org/copyleft/gpl.html
*
* @file
* @author Aaron Schulz
*/
/**
* Class for getting statistically unique IDs
*
* @since 1.21
*/
class UIDGenerator {
/** @var UIDGenerator */
protected static $instance = null;
protected $nodeIdFile; // string; local file path
protected $nodeId32; // string; node ID in binary (32 bits)
protected $nodeId48; // string; node ID in binary (48 bits)
protected $lockFile88; // string; local file path
protected $lockFile128; // string; local file path
/** @var array */
protected $fileHandles = array(); // cache file handles
const QUICK_RAND = 1; // get randomness from fast and insecure sources
const QUICK_VOLATILE = 2; // use an APC like in-memory counter if available
protected function __construct() {
$this->nodeIdFile = wfTempDir() . '/mw-' . __CLASS__ . '-UID-nodeid';
$nodeId = '';
if ( is_file( $this->nodeIdFile ) ) {
$nodeId = file_get_contents( $this->nodeIdFile );
}
// Try to get some ID that uniquely identifies this machine (RFC 4122)...
if ( !preg_match( '/^[0-9a-f]{12}$/i', $nodeId ) ) {
wfSuppressWarnings();
if ( wfIsWindows() ) {
// http://technet.microsoft.com/en-us/library/bb490913.aspx
$csv = trim( wfShellExec( 'getmac /NH /FO CSV' ) );
$line = substr( $csv, 0, strcspn( $csv, "\n" ) );
$info = str_getcsv( $line );
$nodeId = isset( $info[0] ) ? str_replace( '-', '', $info[0] ) : '';
} elseif ( is_executable( '/sbin/ifconfig' ) ) { // Linux/BSD/Solaris/OS X
// See http://linux.die.net/man/8/ifconfig
$m = array();
preg_match( '/\s([0-9a-f]{2}(:[0-9a-f]{2}){5})\s/',
wfShellExec( '/sbin/ifconfig -a' ), $m );
$nodeId = isset( $m[1] ) ? str_replace( ':', '', $m[1] ) : '';
}
wfRestoreWarnings();
if ( !preg_match( '/^[0-9a-f]{12}$/i', $nodeId ) ) {
$nodeId = MWCryptRand::generateHex( 12, true );
$nodeId[1] = dechex( hexdec( $nodeId[1] ) | 0x1 ); // set multicast bit
}
file_put_contents( $this->nodeIdFile, $nodeId ); // cache
}
$this->nodeId32 = wfBaseConvert( substr( sha1( $nodeId ), 0, 8 ), 16, 2, 32 );
$this->nodeId48 = wfBaseConvert( $nodeId, 16, 2, 48 );
// If different processes run as different users, they may have different temp dirs.
// This is dealt with by initializing the clock sequence number and counters randomly.
$this->lockFile88 = wfTempDir() . '/mw-' . __CLASS__ . '-UID-88';
$this->lockFile128 = wfTempDir() . '/mw-' . __CLASS__ . '-UID-128';
}
/**
* @return UIDGenerator
*/
protected static function singleton() {
if ( self::$instance === null ) {
self::$instance = new self();
}
return self::$instance;
}
/**
* Get a statistically unique 88-bit unsigned integer ID string.
* The bits of the UID are prefixed with the time (down to the millisecond).
*
* These IDs are suitable as values for the shard key of distributed data.
* If a column uses these as values, it should be declared UNIQUE to handle collisions.
* New rows almost always have higher UIDs, which makes B-TREE updates on INSERT fast.
* They can also be stored "DECIMAL(27) UNSIGNED" or BINARY(11) in MySQL.
*
* UID generation is serialized on each server (as the node ID is for the whole machine).
*
* @param int $base Specifies a base other than 10
* @return string Number
* @throws MWException
*/
public static function newTimestampedUID88( $base = 10 ) {
if ( !is_integer( $base ) || $base > 36 || $base < 2 ) {
throw new MWException( "Base must an integer be between 2 and 36" );
}
$gen = self::singleton();
$time = $gen->getTimestampAndDelay( 'lockFile88', 1, 1024 );
return wfBaseConvert( $gen->getTimestampedID88( $time ), 2, $base );
}
/**
* @param array $info (UIDGenerator::millitime(), counter, clock sequence)
* @return string 88 bits
* @throws MWException
*/
protected function getTimestampedID88( array $info ) {
list( $time, $counter ) = $info;
// Take the 46 MSBs of "milliseconds since epoch"
$id_bin = $this->millisecondsSinceEpochBinary( $time );
// Add a 10 bit counter resulting in 56 bits total
$id_bin .= str_pad( decbin( $counter ), 10, '0', STR_PAD_LEFT );
// Add the 32 bit node ID resulting in 88 bits total
$id_bin .= $this->nodeId32;
// Convert to a 1-27 digit integer string
if ( strlen( $id_bin ) !== 88 ) {
throw new MWException( "Detected overflow for millisecond timestamp." );
}
return $id_bin;
}
/**
* Get a statistically unique 128-bit unsigned integer ID string.
* The bits of the UID are prefixed with the time (down to the millisecond).
*
* These IDs are suitable as globally unique IDs, without any enforced uniqueness.
* New rows almost always have higher UIDs, which makes B-TREE updates on INSERT fast.
* They can also be stored as "DECIMAL(39) UNSIGNED" or BINARY(16) in MySQL.
*
* UID generation is serialized on each server (as the node ID is for the whole machine).
*
* @param int $base Specifies a base other than 10
* @return string Number
* @throws MWException
*/
public static function newTimestampedUID128( $base = 10 ) {
if ( !is_integer( $base ) || $base > 36 || $base < 2 ) {
throw new MWException( "Base must be an integer between 2 and 36" );
}
$gen = self::singleton();
$time = $gen->getTimestampAndDelay( 'lockFile128', 16384, 1048576 );
return wfBaseConvert( $gen->getTimestampedID128( $time ), 2, $base );
}
/**
* @param array $info (UIDGenerator::millitime(), counter, clock sequence)
* @return string 128 bits
* @throws MWException
*/
protected function getTimestampedID128( array $info ) {
list( $time, $counter, $clkSeq ) = $info;
// Take the 46 MSBs of "milliseconds since epoch"
$id_bin = $this->millisecondsSinceEpochBinary( $time );
// Add a 20 bit counter resulting in 66 bits total
$id_bin .= str_pad( decbin( $counter ), 20, '0', STR_PAD_LEFT );
// Add a 14 bit clock sequence number resulting in 80 bits total
$id_bin .= str_pad( decbin( $clkSeq ), 14, '0', STR_PAD_LEFT );
// Add the 48 bit node ID resulting in 128 bits total
$id_bin .= $this->nodeId48;
// Convert to a 1-39 digit integer string
if ( strlen( $id_bin ) !== 128 ) {
throw new MWException( "Detected overflow for millisecond timestamp." );
}
return $id_bin;
}
/**
* Return an RFC4122 compliant v4 UUID
*
* @param int $flags Bitfield (supports UIDGenerator::QUICK_RAND)
* @return string
* @throws MWException
*/
public static function newUUIDv4( $flags = 0 ) {
$hex = ( $flags & self::QUICK_RAND )
? wfRandomString( 31 )
: MWCryptRand::generateHex( 31 );
return sprintf( '%s-%s-%s-%s-%s',
// "time_low" (32 bits)
substr( $hex, 0, 8 ),
// "time_mid" (16 bits)
substr( $hex, 8, 4 ),
// "time_hi_and_version" (16 bits)
'4' . substr( $hex, 12, 3 ),
// "clk_seq_hi_res (8 bits, variant is binary 10x) and "clk_seq_low" (8 bits)
dechex( 0x8 | ( hexdec( $hex[15] ) & 0x3 ) ) . $hex[16] . substr( $hex, 17, 2 ),
// "node" (48 bits)
substr( $hex, 19, 12 )
);
}
/**
* Return an RFC4122 compliant v4 UUID
*
* @param int $flags Bitfield (supports UIDGenerator::QUICK_RAND)
* @return string 32 hex characters with no hyphens
* @throws MWException
*/
public static function newRawUUIDv4( $flags = 0 ) {
return str_replace( '-', '', self::newUUIDv4( $flags ) );
}
/**
* Return an ID that is sequential *only* for this node and bucket
*
* These IDs are suitable for per-host sequence numbers, e.g. for some packet protocols.
* If UIDGenerator::QUICK_VOLATILE is used the counter might reset on server restart.
*
* @param string $bucket Arbitrary bucket name (should be ASCII)
* @param int $bits Bit size (<=48) of resulting numbers before wrap-around
* @param int $flags (supports UIDGenerator::QUICK_VOLATILE)
* @return float Integer value as float
* @since 1.23
*/
public static function newSequentialPerNodeID( $bucket, $bits = 48, $flags = 0 ) {
return current( self::newSequentialPerNodeIDs( $bucket, $bits, 1, $flags ) );
}
/**
* Return IDs that are sequential *only* for this node and bucket
*
* @see UIDGenerator::newSequentialPerNodeID()
* @param string $bucket Arbitrary bucket name (should be ASCII)
* @param int $bits Bit size (16 to 48) of resulting numbers before wrap-around
* @param int $count Number of IDs to return (1 to 10000)
* @param int $flags (supports UIDGenerator::QUICK_VOLATILE)
* @return array Ordered list of float integer values
* @since 1.23
*/
public static function newSequentialPerNodeIDs( $bucket, $bits, $count, $flags = 0 ) {
$gen = self::singleton();
return $gen->getSequentialPerNodeIDs( $bucket, $bits, $count, $flags );
}
/**
* Return IDs that are sequential *only* for this node and bucket
*
* @see UIDGenerator::newSequentialPerNodeID()
* @param string $bucket Arbitrary bucket name (should be ASCII)
* @param int $bits Bit size (16 to 48) of resulting numbers before wrap-around
* @param int $count Number of IDs to return (1 to 10000)
* @param int $flags (supports UIDGenerator::QUICK_VOLATILE)
* @return array Ordered list of float integer values
* @throws MWException
*/
protected function getSequentialPerNodeIDs( $bucket, $bits, $count, $flags ) {
if ( $count <= 0 ) {
return array(); // nothing to do
} elseif ( $count > 10000 ) {
throw new MWException( "Number of requested IDs ($count) is too high." );
} elseif ( $bits < 16 || $bits > 48 ) {
throw new MWException( "Requested bit size ($bits) is out of range." );
}
$counter = null; // post-increment persistent counter value
// Use APC/eAccelerator/xcache if requested, available, and not in CLI mode;
// Counter values would not survive accross script instances in CLI mode.
$cache = null;
if ( ( $flags & self::QUICK_VOLATILE ) && PHP_SAPI !== 'cli' ) {
try {
$cache = ObjectCache::newAccelerator( array() );
} catch ( Exception $e ) {
// not supported
}
}
if ( $cache ) {
$counter = $cache->incr( $bucket, $count );
if ( $counter === false ) {
if ( !$cache->add( $bucket, (int)$count ) ) {
throw new MWException( 'Unable to set value to ' . get_class( $cache ) );
}
$counter = $count;
}
}
// Note: use of fmod() avoids "division by zero" on 32 bit machines
if ( $counter === null ) {
$path = wfTempDir() . '/mw-' . __CLASS__ . '-' . rawurlencode( $bucket ) . '-48';
// Get the UID lock file handle
if ( isset( $this->fileHandles[$path] ) ) {
$handle = $this->fileHandles[$path];
} else {
$handle = fopen( $path, 'cb+' );
$this->fileHandles[$path] = $handle ?: null; // cache
}
// Acquire the UID lock file
if ( $handle === false ) {
throw new MWException( "Could not open '{$path}'." );
} elseif ( !flock( $handle, LOCK_EX ) ) {
fclose( $handle );
throw new MWException( "Could not acquire '{$path}'." );
}
// Fetch the counter value and increment it...
rewind( $handle );
$counter = floor( trim( fgets( $handle ) ) ) + $count; // fetch as float
// Write back the new counter value
ftruncate( $handle, 0 );
rewind( $handle );
fwrite( $handle, fmod( $counter, pow( 2, 48 ) ) ); // warp-around as needed
fflush( $handle );
// Release the UID lock file
flock( $handle, LOCK_UN );
}
$ids = array();
$divisor = pow( 2, $bits );
$currentId = floor( $counter - $count ); // pre-increment counter value
for ( $i = 0; $i < $count; ++$i ) {
$ids[] = fmod( ++$currentId, $divisor );
}
return $ids;
}
/**
* Get a (time,counter,clock sequence) where (time,counter) is higher
* than any previous (time,counter) value for the given clock sequence.
* This is useful for making UIDs sequential on a per-node bases.
*
* @param string $lockFile Name of a local lock file
* @param int $clockSeqSize The number of possible clock sequence values
* @param int $counterSize The number of possible counter values
* @return array (result of UIDGenerator::millitime(), counter, clock sequence)
* @throws MWException
*/
protected function getTimestampAndDelay( $lockFile, $clockSeqSize, $counterSize ) {
// Get the UID lock file handle
$path = $this->$lockFile;
if ( isset( $this->fileHandles[$path] ) ) {
$handle = $this->fileHandles[$path];
} else {
$handle = fopen( $path, 'cb+' );
$this->fileHandles[$path] = $handle ?: null; // cache
}
// Acquire the UID lock file
if ( $handle === false ) {
throw new MWException( "Could not open '{$this->$lockFile}'." );
} elseif ( !flock( $handle, LOCK_EX ) ) {
fclose( $handle );
throw new MWException( "Could not acquire '{$this->$lockFile}'." );
}
// Get the current timestamp, clock sequence number, last time, and counter
rewind( $handle );
$data = explode( ' ', fgets( $handle ) ); // "<clk seq> <sec> <msec> <counter> <offset>"
$clockChanged = false; // clock set back significantly?
if ( count( $data ) == 5 ) { // last UID info already initialized
$clkSeq = (int)$data[0] % $clockSeqSize;
$prevTime = array( (int)$data[1], (int)$data[2] );
$offset = (int)$data[4] % $counterSize; // random counter offset
$counter = 0; // counter for UIDs with the same timestamp
// Delay until the clock reaches the time of the last ID.
// This detects any microtime() drift among processes.
$time = $this->timeWaitUntil( $prevTime );
if ( !$time ) { // too long to delay?
$clockChanged = true; // bump clock sequence number
$time = self::millitime();
} elseif ( $time == $prevTime ) {
// Bump the counter if there are timestamp collisions
$counter = (int)$data[3] % $counterSize;
if ( ++$counter >= $counterSize ) { // sanity (starts at 0)
flock( $handle, LOCK_UN ); // abort
throw new MWException( "Counter overflow for timestamp value." );
}
}
} else { // last UID info not initialized
$clkSeq = mt_rand( 0, $clockSeqSize - 1 );
$counter = 0;
$offset = mt_rand( 0, $counterSize - 1 );
$time = self::millitime();
}
// microtime() and gettimeofday() can drift from time() at least on Windows.
// The drift is immediate for processes running while the system clock changes.
// time() does not have this problem. See https://bugs.php.net/bug.php?id=42659.
if ( abs( time() - $time[0] ) >= 2 ) {
// We don't want processes using too high or low timestamps to avoid duplicate
// UIDs and clock sequence number churn. This process should just be restarted.
flock( $handle, LOCK_UN ); // abort
throw new MWException( "Process clock is outdated or drifted." );
}
// If microtime() is synced and a clock change was detected, then the clock went back
if ( $clockChanged ) {
// Bump the clock sequence number and also randomize the counter offset,
// which is useful for UIDs that do not include the clock sequence number.
$clkSeq = ( $clkSeq + 1 ) % $clockSeqSize;
$offset = mt_rand( 0, $counterSize - 1 );
trigger_error( "Clock was set back; sequence number incremented." );
}
// Update the (clock sequence number, timestamp, counter)
ftruncate( $handle, 0 );
rewind( $handle );
fwrite( $handle, "{$clkSeq} {$time[0]} {$time[1]} {$counter} {$offset}" );
fflush( $handle );
// Release the UID lock file
flock( $handle, LOCK_UN );
return array( $time, ( $counter + $offset ) % $counterSize, $clkSeq );
}
/**
* Wait till the current timestamp reaches $time and return the current
* timestamp. This returns false if it would have to wait more than 10ms.
*
* @param array $time Result of UIDGenerator::millitime()
* @return array|bool UIDGenerator::millitime() result or false
*/
protected function timeWaitUntil( array $time ) {
do {
$ct = self::millitime();
if ( $ct >= $time ) { // http://php.net/manual/en/language.operators.comparison.php
return $ct; // current timestamp is higher than $time
}
} while ( ( ( $time[0] - $ct[0] ) * 1000 + ( $time[1] - $ct[1] ) ) <= 10 );
return false;
}
/**
* @param array $time Result of UIDGenerator::millitime()
* @return string 46 MSBs of "milliseconds since epoch" in binary (rolls over in 4201)
* @throws MWException
*/
protected function millisecondsSinceEpochBinary( array $time ) {
list( $sec, $msec ) = $time;
$ts = 1000 * $sec + $msec;
if ( $ts > pow( 2, 52 ) ) {
throw new MWException( __METHOD__ .
': sorry, this function doesn\'t work after the year 144680' );
}
return substr( wfBaseConvert( $ts, 10, 2, 46 ), -46 );
}
/**
* @return array (current time in seconds, milliseconds since then)
*/
protected static function millitime() {
list( $msec, $sec ) = explode( ' ', microtime() );
return array( (int)$sec, (int)( $msec * 1000 ) );
}
/**
* Delete all cache files that have been created.
*
* This is a cleanup method primarily meant to be used from unit tests to
* avoid poluting the local filesystem. If used outside of a unit test
* environment it should be used with caution as it may destroy state saved
* in the files.
*
* @see unitTestTearDown
* @since 1.23
*/
protected function deleteCacheFiles() {
// Bug: 44850
foreach ( $this->fileHandles as $path => $handle ) {
if ( $handle !== null ) {
fclose( $handle );
}
if ( is_file( $path ) ) {
unlink( $path );
}
unset( $this->fileHandles[$path] );
}
if ( is_file( $this->nodeIdFile ) ) {
unlink( $this->nodeIdFile );
}
}
/**
* Cleanup resources when tearing down after a unit test.
*
* This is a cleanup method primarily meant to be used from unit tests to
* avoid poluting the local filesystem. If used outside of a unit test
* environment it should be used with caution as it may destroy state saved
* in the files.
*
* @see deleteCacheFiles
* @since 1.23
*/
public static function unitTestTearDown() {
// Bug: 44850
$gen = self::singleton();
$gen->deleteCacheFiles();
}
function __destruct() {
array_map( 'fclose', array_filter( $this->fileHandles ) );
}
}
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