mongo::DistributedLock Class Reference

#include <distlock.h>

Public Member Functions
	DistributedLock (const ConnectionString &conn, const string &name, unsigned takeoverMinutes=15)
bool	lock_try (string why, BSONObj *other=0)
void	unlock ()
Private Attributes
ConnectionString	_conn
BSONObj	_id
string	_name
string	_ns
unsigned	_takeoverMinutes

Detailed Description

The distributed lock is a configdb backed way of synchronizing system-wide tasks. A task must be identified by a unique name across the system (e.g., "balancer"). A lock is taken by writing a document in the configdb's locks collection with that name.

To be maintained, each taken lock needs to be revalidaded ("pinged") within a pre-established amount of time. This class does this maintenance automatically once a DistributedLock object was constructed.

Definition at line 35 of file distlock.h.

Constructor & Destructor Documentation

mongo::DistributedLock::DistributedLock	(	const ConnectionString &	conn,
		const string &	name,
		unsigned	takeoverMinutes = `15`
	)

The constructor does not connect to the configdb yet and constructing does not mean the lock was acquired. Construction does trigger a lock "pinging" mechanism, though.

Parameters:

	conn	address of config(s) server(s)
	name	identifier for the lock
	takeoverMinutes	how long can the log go "unpinged" before a new attempt to lock steals it (in minutes)

Member Function Documentation

bool mongo::DistributedLock::lock_try	(	string	why,
		BSONObj *	other = `0`
	)

Attempts to aquire 'this' lock, checking if it could or should be stolen from the previous holder. Please consider using the dist_lock_try construct to acquire this lock in an exception safe way.

Parameters:

	why	human readable description of why the lock is being taken (used to log)
	other	configdb's lock document that is currently holding the lock, if lock is taken