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store some lock-data, so only a single callback calculate data on cache-miss

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done to avoid race-conditions where many processes try to fetch and therefore calculate some expensive to calculate data
eg. mass-mailings in our hosting
This commit is contained in:
Ralf Becker 2021-05-26 11:38:24 +02:00
parent 691fb06de5
commit cda95d8188
2 changed files with 80 additions and 35 deletions
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113
api/src/Cache.php
View File

@ -28,10 +28,10 @@ namespace EGroupware\Api;
* getXXX($app,$location,$callback=null,array $callback_params,$expiration=0)
* has three optional parameters allowing to specify:
* 3. a callback if requested data is not yes stored. In that case the callback is called
* and it's value is stored in the cache AND retured
* and it's value is stored in the cache AND returned
* 4. parameters to pass to the callback as array, see call_user_func_array
* 5. an expiration time in seconds to specify how long data should be cached,
* default 0 means infinit (this time is not supported for request level!)
* default 0 means infinite (this time is not supported for request level!)
*
* Data is stored under an application name and a location, like egw_session::appsession().
* In fact data stored at cache level Api\Cache::SESSION, is stored in the same way as
@ -42,14 +42,23 @@ namespace EGroupware\Api;
* The tree and instance wide cache uses a certain provider class, to store the data
* eg. in memcached or if there's nothing else configured in the filesystem (eGW's temp_dir).
*
* "Admin >> clear cache and register hooks" allways only clears instance level cache of
* "Admin >> clear cache and register hooks" always only clears instance level cache of
* calling instance. It never clears tree level cache, which makes it important to set
* resonable expiry times or think about an other means of clearing that particular item.
* reasonable expiry times or think about an other means of clearing that particular item.
* (Not clearing of tree-level cache is important, as regenerating it is an expensive
* operation for a huge scale EGroupware hosting operation.)
*
* Apps needing to talk to multiple EGroupware instances (eg. Stylite Managementserver)
* Apps needing to talk to multiple EGroupware instances (eg. EGroupware Managementserver)
* can use install_id of instance as $level parameter to (set|get|unset)Cache method.
*
* If a callback is used to calculate the data, in case it's not found in the cache, e.g.:
* $data = Api\Cache::getCache(Api\Cache::(TREE|INSTANCE), $app, $location, function($params)
* {
* // code to calculate / query $data
* return $data;
* }, $params, $expiration);
* then we lock the $app:$location by storing some specific data, so only one callback is used
* to calculate the data, and other processes sleep until the data is calculate to avoid races.
*/
class Cache
{
@ -108,7 +117,7 @@ class Cache
* @param int $expiration =0 expiration time in seconds, default 0 = never
* @return boolean true if data could be stored, false otherwise incl. key already existed
*/
static public function addCache($level,$app,$location,$data,$expiration=0)
public static function addCache($level,$app,$location,$data,$expiration=0)
{
//error_log(__METHOD__."('$level','$app','$location',".array2string($data).",$expiration)");
switch($level)
@ -144,7 +153,7 @@ class Cache
* @param int $expiration =0 expiration time in seconds, default 0 = never
* @return boolean true if data could be stored, false otherwise
*/
static public function setCache($level,$app,$location,$data,$expiration=0)
public static function setCache($level,$app,$location,$data,$expiration=0)
{
//error_log(__METHOD__."('$level','$app','$location',".array2string($data).",$expiration)");
switch($level)
@ -170,6 +179,19 @@ class Cache
throw new Exception\WrongParameter(__METHOD__."() unknown level '$level'!");
}
/**
* Content stored to signal one callback is already running and calculating the data, to not run it multiple times
*/
const CALLBACK_LOCK = '***LOCKED***';
/**
* Maximum time an item is locked, to recover from eg. a crash while the lock is set
*/
const CALLBACL_LOCK_TIMEOUT = 10; // 10s
/**
* Time other processes sleep to wait for one callback to calculate the data
*/
const CALLBACK_LOCK_USLEEP = 50000; // 50ms
/**
* Get some data from the cache
*
@ -182,7 +204,7 @@ class Cache
* @return mixed NULL if data not found in cache (and no callback specified) or
* if $location is an array: location => data pairs for existing location-data, non-existing is not returned
*/
static public function getCache($level,$app,$location,$callback=null,array $callback_params=array(),$expiration=0)
public static function getCache($level,$app,$location,$callback=null,array $callback_params=array(),$expiration=0)
{
switch($level)
{
@ -224,16 +246,39 @@ class Cache
}
else
{
$data = $provider->get($keys=self::keys($level,$app,$location));
if (is_null($data) && !is_null($callback))
// try reading cached data and, if not found AND a callback to do so given, calculate it
// only allow one process to do the (heavy) calculation by storing some lock-data
// other processes reading the lock-data sleep for a short time, before try reading it again
for($n=10+self::CALLBACL_LOCK_TIMEOUT*1000000/self::CALLBACK_LOCK_USLEEP; $n >= 0; $n--)
{
$data = call_user_func_array($callback,$callback_params);
// limit expiration to configured maximum time
if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
$data = $provider->get($keys=self::keys($level,$app,$location));
if ($data === self::CALLBACK_LOCK)
{
$expiration = self::$max_expiration;
usleep(self::CALLBACK_LOCK_USLEEP);
}
elseif($data === null && isset($callback))
{
$provider->set($keys, self::CALLBACK_LOCK, self::CALLBACL_LOCK_TIMEOUT);
try {
$data = call_user_func_array($callback, $callback_params);
}
catch(\Throwable $e) {
// remove lock, before re-throwing the exception/error
$provider->delete($keys);
throw $e;
}
// limit expiration to configured maximum time
if (isset(self::$max_expiration) && (!$expiration || $expiration > self::$max_expiration))
{
$expiration = self::$max_expiration;
}
$provider->set($keys, $data, $expiration);
break;
}
else
{
break;
}
$provider->set($keys,$data,$expiration);
}
}
}
@ -254,7 +299,7 @@ class Cache
* @param string $location location name for data
* @return boolean true if data was set, false if not (like isset())
*/
static public function unsetCache($level,$app,$location)
public static function unsetCache($level,$app,$location)
{
switch($level)
{
@ -283,7 +328,7 @@ class Cache
* @param int $expiration =0 expiration time in seconds, default 0 = never
* @return boolean true if data could be stored, false otherwise
*/
static public function setTree($app,$location,$data,$expiration=0)
public static function setTree($app,$location,$data,$expiration=0)
{
//error_log(__METHOD__."('$app','$location',".array2string($data).",$expiration)");
return self::setCache(self::TREE,$app,$location,$data,$expiration);
@ -299,7 +344,7 @@ class Cache
* @param int $expiration =0 expiration time in seconds, default 0 = never
* @return mixed NULL if data not found in cache (and no callback specified)
*/
static public function getTree($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
public static function getTree($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
{
return self::getCache(self::TREE,$app,$location,$callback,$callback_params,$expiration);
}
@ -311,7 +356,7 @@ class Cache
* @param string $location location name for data
* @return boolean true if data was set, false if not (like isset())
*/
static public function unsetTree($app,$location)
public static function unsetTree($app,$location)
{
return self::unsetCache(self::TREE,$app,$location);
}
@ -325,7 +370,7 @@ class Cache
* @param int $expiration =0 expiration time in seconds, default 0 = never
* @return boolean true if data could be stored, false otherwise
*/
static public function setInstance($app,$location,$data,$expiration=0)
public static function setInstance($app,$location,$data,$expiration=0)
{
return self::setCache(self::INSTANCE,$app,$location,$data,$expiration);
}
@ -340,7 +385,7 @@ class Cache
* @param int $expiration =0 expiration time in seconds, default 0 = never
* @return mixed NULL if data not found in cache (and no callback specified)
*/
static public function getInstance($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
public static function getInstance($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
{
return self::getCache(self::INSTANCE,$app,$location,$callback,$callback_params,$expiration);
}
@ -352,7 +397,7 @@ class Cache
* @param string $location location name for data
* @return boolean true if data was set, false if not (like isset())
*/
static public function unsetInstance($app,$location)
public static function unsetInstance($app,$location)
{
return self::unsetCache(self::INSTANCE,$app,$location);
}
@ -371,7 +416,7 @@ class Cache
* @param int $expiration =0 expiration time in seconds, default 0 = never
* @return boolean true if data could be stored, false otherwise
*/
static public function setSession($app,$location,$data,$expiration=0)
public static function setSession($app,$location,$data,$expiration=0)
{
if (isset($_SESSION[Session::EGW_SESSION_ENCRYPTED]))
{
@ -400,7 +445,7 @@ class Cache
* @param int $expiration =0 expiration time in seconds, default 0 = never
* @return mixed NULL if data not found in cache (and no callback specified)
*/
static public function &getSession($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
public static function &getSession($app, $location, $callback=null, array $callback_params=array(), $expiration=0)
{
if (isset($_SESSION[Session::EGW_SESSION_ENCRYPTED]))
{
@ -429,7 +474,7 @@ class Cache
* @param string $location location name for data
* @return boolean true if data was set, false if not (like isset())
*/
static public function unsetSession($app,$location)
public static function unsetSession($app,$location)
{
if (isset($_SESSION[Session::EGW_SESSION_ENCRYPTED]))
{
@ -468,7 +513,7 @@ class Cache
* @param int $expiration =0 expiration time is NOT used for REQUEST!
* @return boolean true if data could be stored, false otherwise
*/
static public function setRequest($app,$location,$data,$expiration=0)
public static function setRequest($app,$location,$data,$expiration=0)
{
unset($expiration); // not used, but required by function signature
self::$request_cache[$app][$location] = $data;
@ -486,7 +531,7 @@ class Cache
* @param int $expiration =0 expiration time is NOT used for REQUEST!
* @return mixed NULL if data not found in cache (and no callback specified)
*/
static public function getRequest($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
public static function getRequest($app,$location,$callback=null,array $callback_params=array(),$expiration=0)
{
unset($expiration); // not used, but required by function signature
if (!isset(self::$request_cache[$app][$location]) && !is_null($callback))
@ -503,7 +548,7 @@ class Cache
* @param string $location location name for data
* @return boolean true if data was set, false if not (like isset())
*/
static public function unsetRequest($app,$location)
public static function unsetRequest($app,$location)
{
if (!isset(self::$request_cache[$app][$location]))
{
@ -521,7 +566,7 @@ class Cache
*
* @param string $level Api\Cache::(TREE|INSTANCE) or install_id
* @param boolean $log_not_found =true false do not log if no provider found, used eg. to supress error via unsetCache during installation
* @return Api\Cache\Provider
* @return Cache\Provider|Cache\ProviderMultiple
*/
static protected function get_provider($level, $log_not_found=true)
{
@ -602,7 +647,7 @@ class Cache
* @param boolean $throw =true throw an exception, if we can't retriev the value
* @return string|boolean string with config or false if not found and !$throw
*/
static public function get_system_config($name,$throw=true)
public static function get_system_config($name, $throw=true)
{
if(!isset($GLOBALS['egw_info']['server'][$name]))
{
@ -642,7 +687,7 @@ class Cache
* @param string $level =self::INSTANCE
* @param string $app =null app-name or "all" to empty complete cache
*/
static public function flush($level=self::INSTANCE, $app=null)
public static function flush($level=self::INSTANCE, $app=null)
{
$ret = true;
if (!($provider = self::get_provider($level)))
@ -670,7 +715,7 @@ class Cache
/**
* Unset instance key, so it get read again and re-read install_id from database
*/
static public function unset_instance_key()
public static function unset_instance_key()
{
self::$instance_key = null;
$GLOBALS['egw_info']['server']['install_id'] = self::get_system_config('install_id', false);
@ -689,7 +734,7 @@ class Cache
* @param string $install_id =null default use install_id of current instance
* @return string new key also stored in self::$instance_key
*/
static public function generate_instance_key($install_id=null)
public static function generate_instance_key($install_id=null)
{
if (!isset($install_id))
{
@ -711,7 +756,7 @@ class Cache
* @param string $location =null
* @return array
*/
static public function keys($level, $app=null, $location=null)
public static function keys($level, $app=null, $location=null)
{
static $tree_key = null;

2
api/src/Cache/ProviderMultiple.php
View File

@ -16,7 +16,7 @@ namespace EGroupware\Api\Cache;
/**
* Interface for a caching provider being able to retrieve multiple entires
*/
interface ProviderMultiple
interface ProviderMultiple extends Provider
{
/**
* Get multiple data from the cache