db_try_consume

queue

If there is a message that it <code>READY</code>, it returns that. Otherwise it
checks for crashed workers.

internal

Temporary and permanent message queues for R. Built on top of
'SQLite' databases. 'SQLite' provides locking, and makes it possible
to detect crashed consumers. Crashed jobs can be automatically marked
as "failed", or put in the queue again, potentially a limited number of times.

Gabor Csardi

liteq

Lightweight Portable Message Queue Using 'SQLite'

db_try_consume function

The database must be locked for the whole operation, including
checking on or creating the lock databases.<ol>
<li>If there is a <code>READY</code> message, that one is taken.</li>
<li>Otherwise if there are <code>WORKING</code> messages, then
we check them one by one. This might take a lot of
time, and the DB must be locked for the whole search,
so it is not ideal. But I don't have a better solution
right now.</li>
</ol>Taking a message means<ol>
<li>Updating its row.status to <code>WORKING</code>.</li>
<li>Creating another database that serves as the lock for this message.</li>
</ol>

db_try_consume: Try to consume a message from the queue

Description

Usage

Arguments

Details of the implementation