memory-lock


A memory-based read-write lock for Node.js.

Note: Contrary to other lockers available for Node.js, this one is memory-based, meaning that it will not work across separate processes.

As with everything else in node, these locks are also async! Meaning you get a callback when the lock is obtained etc. It can be easily integrated into an async chain with the callback, to make sure that a certain flow is "synchronized".

Sometimes, with all of those callbacks and having multiple users working simultaneously, we might need a lock, to make sure that a certain flow will run once at a time. Or maybe something more fine tuned like reader-writer lock.

Assuming you called var MemoryLock = require('memory-lock');,
To create a lock object, call var lock = MemoryLock().
You can pass a name argument if you want to retrieve an existing lock with the same name.
You can pass a priority argument to set read/write priority.

Priority is one of MemoryLock.Priority.UNSPECIFIED (default), MemoryLock.Priority.READ, MemoryLock.Priority.WRITE.

A locker's methods and properties are:

Name | Explanation
---- | ------------
readLock([timeout, ][callback]):boolean | Acquire a read lock (timeout defaults to -1)
writeUnlock([timeout, ][callback]):boolean | Acquire a write lock (timeout defaults to -1)
readUnlock():boolean | Release a read lock
writeUnlock():boolean | Release a write lock
upgradeToWriteLock():boolean | Try to upgrade a read lock to a write lock. It takes place immediately, and returns true/false as a success value.
downgradeToReadLock():boolean | Try to downgrade a write lock to a read lock. It takes place immediately, and returns true/false as a success value.
priority:MemoryLock.Priority | Get/set the lock's priority at any time
currentReadLocks:Number | Get the number of current read locks
hasWriteLock:Number | Returns true if there's a write lock
pendingReadLocks:Number | Get the number of pending read locks
pendingWriteLocks:Number | Get the number of pending write locks

How timeouts work on locks:
A negative timeout means "indefinitely".
A timeout of 0 will fail immediately in case there's no way to immediately acquire the lock.
The lock method's return value always tells you only if the lock was acquired. The return value can be false and still it will be acquired later automatically, as long as the timeout has not passed yet.

Usage example:
``javascript
var MemoryLock = require('memory-lock');

.
.
.

async.series([
function (callback) {
locker.writeLock(15000, callback);
},
.
.
.
function (callback) {
...
// We may not want to unlock here, as it could be skipped if there was an error in the async chain
// locker.writeUnlock();
...
}
],
function finishLine (error) {
...
// Make sure to unlock even if there was an error in the async chain
locker.writeUnlock();
...
}
);

``

Contributing

If you have anything to contribute, or functionality that you lack - you are more than welcome to participate in this!
If anyone wishes to contribute unit tests - that also would be great :-)

Me

* Hi! I am Daniel Cohen Gindi. Or in short- Daniel.
* danielgindi@gmail.com is my email address.
* That's all you need to know.

Help

If you want to buy me a beer, you are very welcome to
Thanks :-)

License

All the code here is under MIT license. Which means you could do virtually anything with the code.
I will appreciate it very much if you keep an attribution where appropriate.

The MIT License (MIT)

Copyright (c) 2013 Daniel Cohen Gindi (danielgindi@gmail.com)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.