expirable-synchronized

A JavaScript decorator to atomize any function that returns promise. The waiting to resolve can expire after some time.

Similar to Java's @synchronized, this decorator can atomize a function!

If you add this decorator to a function that returns a promise, and call this function multiple times, the function calls will be executed in a certain way. There are two modes:

• Fair: @expirableSynchronized or @expirableSynchronizedFair

  Queue up all function calls. The next function call in the queue can only start after the previous one finishes. The function acts like a fair lock added.

• Exclusive: @expirableSynchronizedExclusive

  Drop all other function calls when there is a function call that hasn't finished.

The function to apply this decorator must return a promise

Notice that this decorator doesn't affect the promise itself, just set when / whether to execute them.

Use Case:

When you want to use it & Solutions if you don't really need it:

• The function has asynchronous jobs and the order matters. (Otherwise, you don't need to do anything.)
• The function is not called by your program, or it's hard to manage the function caller. A typical example is event listener. (Otherwise, you should refactor your code to better call your function.)
• You need the expiration of waiting to resolve. (Otherwise, consider using RxJS's asyncScheduler, schedule in a subscription.)
• If RxJS is too big for your project to include. (Otherwise, RxJS is your answer if you don't need the expiration of waiting to resolve.)

How it works:

Fair:

It connects all function calls into a promise chain. It's safe because you can set an expiry time to stop waiting for the promise to resolve. If one call in the chain takes too long to resolve / reject, the next in the chain will be executed.

It uses a pointer to build promise chain. The promise is saved in the function's target(who calls the function). This target is the class instance in most cases.

Exclusive:

It locks the function when a function call starts, release it when it's done. No other function call by the same caller can run when this function is locked, and won't run later.

Installation

Using npm:

npm install --save expirable-synchronized

Using yarn:

yarn add expirable-synchronized

Requirements

• An environment that supports stage-0 of the decorators spec.
• Node 8+.

If you use transpiler

• For Babel: You need a decorator plugin
  • For Babel 6
  • For Babel 7
• For TypeScript: You need to turn on experimentalDecorators. Official docs

How to Use

Just add @expirableSynchronized() or @expirableSynchronizedExclusive() above the function that returns a promise. According to current stage of decorator proposal, the function has to be a class member.

class Example {
    @expirableSynchronized()
    anyFunctionThatReturnsAPromise() {
        // ...
    }

    @expirableSynchronized(2000)
    anyFunctionThatReturnsAPromise2() {
        // ...
    }

    @expirableSynchronized(2000, 'your-custom-prefix-')
    anyFunctionThatReturnsAPromise3() {
        // ...
    }

    @expirableSynchronizedExclusive()
    anyFunctionThatReturnsAPromise4() {
        // ...
    }

    @expirableSynchronizedExclusive(2000)
    anyFunctionThatReturnsAPromise5() {
        // ...
    }

    @expirableSynchronizedExclusive(2000, 'your-custom-prefix-')
    anyFunctionThatReturnsAPromise6() {
        // ...
    }
}

Options

Parameter	Description	Type	Default Value
life	The promise life limit. After this amount of time, the next promise in chain will be executed anyway in Fair mode, lock will be released anyway in Exclusive mode Default value is 5 seconds (other packages like jest has 5s as timeout also)	number	5000
prefix	The prefix for the name of lock / promise pointer living in the caller object (class instance). Only set this parameter in case that the default prefix has conflict with your existing object key	string	expirable-synchronized-