Update handlers.lua

[elliotsayes]

Handlers.once does a prepend: these should be higher priority than fallback handles.

Use case: worker pool.

• Scenario 1: The master process resets a workers "busy" status upon receiving a "Ready" message.
• Scenario 2: When the all workers are busy, the master process should suspend by doing Receive on (any) workers "Ready" message. Resuming the thread should take priority over resetting the status as in Scenario 1

[kprimice]

I encountered a similar issue in a different scenario:

In my case, a process (Process A) interacts with a Liquidity Pool, receiving Credit-Notice messages. However, these Credit-Notice messages need to prepend to ensure that Process A processes them immediately, without interference from the main Credit-Notice handler.

Currently, the main handler is interfering, which prevents the Credit-Notice messages (coming from the Liquidity Pool)
from being handled with the necessary priority, and forces me to add exceptions to the main Credit-Notice handler.

[twilson63]

Sounds good, I am going to try to include this in the 2.0.1 release we are hoping to ship today or tomorrow, are we sure prepend is the way to go for (once) as a default, any reasons not to make this the default?

[elliotsayes]

are we sure prepend is the way to go for (once) as a default, any reasons not to make this the default?

I've been thinking about this a bit, prepend also has its downsides... e.g., you expect the first call to once to take precedence over later calls.
Maybe the "proper" way to do this is to have priority levels for the handles?

[twilson63]

Lets go with prepend for now, and we can look at priorities in the future