Detailed Description

Interface for distributed lock strategies.

Example

class MockDistLockStrategy final : public dist_lock::DistLockStrategyBase {
 public:
  ~MockDistLockStrategy() override { EXPECT_FALSE(IsLocked()); }
 
  void Acquire(std::chrono::milliseconds,
               const std::string& locker_id) override {
    UASSERT(!locker_id.empty());
    attempts_++;
    auto locked_by = locked_by_var_.Lock();
    if (!locked_by->empty() && *locked_by != locker_id)
      throw dist_lock::LockIsAcquiredByAnotherHostException();
    if (!allowed_) throw std::runtime_error("not allowed");
    *locked_by = locker_id;
  }
 
  void Release(const std::string& locker_id) override {
    auto locked_by = locked_by_var_.Lock();
    if (*locked_by == locker_id) locked_by->clear();
  }
 
  bool IsLocked() {
    auto locked_by = locked_by_var_.Lock();
    return !locked_by->empty();
  }
 
  void Allow(bool allowed) { allowed_ = allowed; }
 
  void SetLockedBy(const std::string& whom) {
    auto locked_by = locked_by_var_.Lock();
    *locked_by = whom;
  }
 
  size_t GetAttemptsCount() const { return attempts_; }
 
 private:
  concurrent::Variable<std::string> locked_by_var_;
  std::atomic<bool> allowed_{false};
  std::atomic<size_t> attempts_{0};
};

Definition at line 24 of file dist_lock_strategy.hpp.

Inheritance diagram for dist_lock::DistLockStrategyBase:

Public Member Functions
virtual void	Acquire (std::chrono::milliseconds lock_ttl, const std::string &locker_id)=0

virtual void	Release (const std::string &locker_id)=0

Member Function Documentation

◆ Acquire()

virtual void dist_lock::DistLockStrategyBase::Acquire	(	std::chrono::milliseconds	lock_ttl,
		const std::string &	locker_id )

pure virtual

Acquires the distributed lock.

Parameters

lock_ttl	The duration for which the lock must be held.
locker_id	Globally unique ID of the locking entity.

Exceptions

LockIsAcquiredByAnotherHostError	when the lock is busy
anything	else when the locking fails, strategy is responsible for cleanup, Release won't be invoked.

Implemented in storages::mongo::DistLockStrategy, and storages::postgres::DistLockStrategy.