NamedLock class

A NamedLock can be used to control access to a resource across processes and isolates.

A NamedLock uses a combination of a UDP socket and a files to provide a locking mechanism that is guarenteed to work across isolates in the same process as well as between processes.

If you only need locking 'within' an isolate that you should avoid using NamedLock as it is a realitively slow locking mechanism as it creates a file to represent a lock.

To ensure that NamedLocks hold across processes and isolates we use a two part locking mechanism. The first part is a UDP socket (on port 63424) that we refere to a hard lock. The same hard lock is used for all NamedLocks and as such is a potential bottle neck. To limit this bottle neck we hold the hard lock for as short a period as possible. The hard lock is only used to create and delete the file based lock. As soon as a file based lock transition completes the hard lock is released.

On linux a traditional file lock will not block isolates in the same process from locking the same file hence we need

Constructors

NamedLock({required String name, String? lockPath, String description = '', Duration timeout = const Duration(seconds: 30)})
lockPath is the path of the directory used to store the lock file. If no lockPath is given then Directory.systemTemp/dcli/locks is used to store locks. All code that shares the lock MUST use the same lockPath. It is recommended that you pass an absolute path to ensure that the same path is used. The name is used as the suffix of the lockfile. The suffix allows multiple locks to share a single lockPath. The description, if passed, is used in error messages to describe the lock. The timeout defines how long we will wait for a lock to become available. The default timeout is infinite (null).

Properties

decLockCount → int
decrements the lock count and returns the new lock count.
no setter
hashCode → int
The hash code for this object.
no setterinherited
incLockCount → int
increments the lock count and returns the new lock count.
no setter
name → String
The name of the lock.
final
port → int
The tcp socket port we use to implement a hard lock. A port can only be opened once so its the perfect way to create a lock that works across processes and isolates.
final
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
toString() → String
A string representation of this object.
inherited
withLock(void fn(), {String? waiting}) → void
creates a lock file and then calls fn once fn returns the lock is released. If waiting is passed it will be used to write a log message to the console.

Operators

operator ==(Object other) → bool
The equality operator.
inherited