| date | comment |
|---|---|
| 202109 | reviewed - no change |
| Table of Contents |
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Data Sources
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- DTO - Data Transfer Object is same object end-users see/use when making API calls.
- DBO - Database Object is a POJO that maps directly to table. For every column of the table there will be a matching field in the corresponding DBO. See Adding New Database Objects
- DAO - Data Access Object is the abstraction that translates to DTOs into DBOs directly performs all datasource CRUD.
- CRUD - Create, Read, Update, and Delete.
Workers
The workers war is composed of many workers each performing separate tasks. The following diagram shows the components of a typical worker using "search" as an example:
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When the scheduler fires according to the trigger, the SemaphoreGatedRunner's execute methods is called. The semaphore will generate a random number between 0 and the maximum number of workers of that type (exclusive) and concatenate that number with the worker's unique key to generate a lock string. It will then attempt to acquire a global lock on that string using the semaphore RDS table. If a lock is acquired, it will be held in a try/finally block while configured runner is executed. It will unconditional unconditionally release the lock when the Runner's run() method returns.
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- When lock is issued, it is guaranteed to be held until released by the lock holder or the configured timeout is exceeded.
- The same lock will not be issued to multiple callers.
- Lock acquisition is non-blocking, meaning it does not wait for a lock to be acquire. In other words, the SemaphoreGatedRunner will return to the caller immediately if a lock cannot be acquired.
- When a lock is acquired a new unique token is issued to the lock holder. This token must be used to release the lock. The means if one thread is issued a lock but does not release it before the configured timeout is exceed, then the same lock can be issued to another thread but with a new token. Since the original thread's token is no longer bound to the lock it cannot , that token cannot be used to release the lock since it had been re-issued to the other caller.
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