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#pragma once
#include <Common/ZooKeeper/ZooKeeper.h>
#include <Common/ZooKeeper/KeeperException.h>
#include <memory>
#include <string>
namespace Poco { class Logger; }
namespace zkutil
{
/** Caveats: usage of locks in ZooKeeper is incorrect in 99% of cases,
* and highlights your poor understanding of distributed systems.
*
* It's only correct if all the operations that are performed under lock
* are atomically checking that the lock still holds
* or if we ensure that these operations will be undone if lock is lost
* (due to ZooKeeper session loss) that's very difficult to achieve.
*
* It's Ok if every operation that we perform under lock is actually operation in ZooKeeper.
*
* In 1% of cases when you can correctly use Lock, the logic is complex enough, so you don't need this class.
*
* TLDR: Don't use this code if you are not sure. We only have a few cases of it's usage.
*/
class ZooKeeperLock
{
public:
/// lock_prefix - path where the ephemeral lock node will be created
/// lock_name - the name of the ephemeral lock node
ZooKeeperLock(
const ZooKeeperPtr & zookeeper_,
const std::string & lock_prefix_,
const std::string & lock_name_,
const std::string & lock_message_ = "");
~ZooKeeperLock();
void unlock();
bool tryLock();
bool isLocked() const;
const std::string & getLockPath() const;
private:
zkutil::ZooKeeperPtr zookeeper;
std::string lock_path;
std::string lock_message;
Poco::Logger * log;
bool locked = false;
};
std::unique_ptr<ZooKeeperLock> createSimpleZooKeeperLock(
const ZooKeeperPtr & zookeeper, const String & lock_prefix, const String & lock_name, const String & lock_message);
}
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