/**
* Puts shallow read and/or write locks on files
*
* Resources with a shallow lock on it can only be modified in the same
* request as they were placed and not by parallel requests (in different
* server threads/processes). However, as soon as the request ends, the lock
* will be released.
*
* Write locks can not be set if there is already a read or write lock set.
* Read locks can not be set if there is already a write lock set. There can
* be multiple read locks on the same resource!
*
* @param array $write paths to write-lock, use an empty array to skip
* @param array $read paths to read-lock
* @return void
*/
public function shallowLock($write, $read = array())
{
$whashes = $rhashes = array();
foreach ($write as $value) {
$whashes[] = BeeHub_DB::escape_string(hash('sha256', $value, true));
}
foreach ($read as $value) {
$rhashes[] = BeeHub_DB::escape_string(hash('sha256', $value, true));
}
sort($whashes, SORT_STRING);
sort($rhashes, SORT_STRING);
if (!empty($whashes)) {
BeeHub_DB::query('INSERT IGNORE INTO `shallowLocks` VALUES (' . implode('),(', $whashes) . ');');
$whashes = implode(',', $whashes);
$whashes = "SELECT * FROM `shallowLocks` WHERE `pathhash` IN ({$whashes}) FOR UPDATE;";
} else {
$whashes = null;
}
if (!empty($rhashes)) {
BeeHub_DB::query('INSERT IGNORE INTO `shallowLocks` VALUES (' . implode('),(', $rhashes) . ');');
$rhashes = implode(',', $rhashes);
$rhashes = "SELECT * FROM `shallowLocks` WHERE `pathhash` IN ({$rhashes}) LOCK IN SHARE MODE;";
} else {
$rhashes = null;
}
$microsleeptimer = 10000;
// also functions as success flag
while ($microsleeptimer) {
if ($microsleeptimer > 1280000) {
$microsleeptimer = 1280000;
}
BeeHub_DB::query('START TRANSACTION');
if ($whashes) {
try {
BeeHub_DB::query($whashes)->free_result();
} catch (BeeHub_Deadlock $e) {
BeeHub_DB::query('ROLLBACK');
usleep($microsleeptimer);
$microsleeptimer *= 2;
continue;
} catch (BeeHub_Timeout $e) {
BeeHub_DB::query('ROLLBACK');
throw new DAV_Status(DAV::HTTP_SERVICE_UNAVAILABLE);
}
}
if ($rhashes) {
try {
BeeHub_DB::query($rhashes)->free_result();
} catch (BeeHub_Deadlock $e) {
BeeHub_DB::query('ROLLBACK');
usleep($microsleeptimer);
$microsleeptimer *= 2;
continue;
} catch (BeeHub_Timeout $e) {
BeeHub_DB::query('ROLLBACK');
throw new DAV_Status(DAV::HTTP_SERVICE_UNAVAILABLE);
}
}
$microsleeptimer = 0;
}
}
