The active object pattern
To overcome the preceding race condition in concurrency, we can use the active object pattern.
Note
The active object pattern decouples the method execution from its invocation. Mostly, the active object pattern executes in asynchronous mode. Requesters submit a task as an object in a queue, and a scheduler picks an object from the queue and executes its logic. An object in the queue knows what to do when invoked, and that's the reason why the name of the pattern is active object.
As Apex does not support multithreading, we cannot create a shareable queue, which can be accessed by multiple threads simultaneously; and therefore, we will do it with the help of the Pending_Request__c custom object. This custom object will save all the necessary information of the pending tasks that need to be performed asynchronously by the active object pattern.
Note
Do not confuse a shareable queue with the Salesforce queue. Here, a queue means a list of objects available in memory...
