Set or view the number of 'daemons' or persistent server processes receiving mirai requests. These are, by default, automatically created on the local machine. Alternatively, a client URL may be set to receive connections from remote servers started with server, for distributing tasks across the network.

daemons(n, .url)

Arguments

n

integer number of daemons to set | 'view' to view the current number of daemons.

.url

(optional) for distributing tasks across the network: character client URL and port accepting incoming connections e.g. 'tcp://192.168.0.2:5555' at which server processes started using server should connect to. To listen to port 5555 (for example) on all interfaces on the host, specify one of 'tcp://:5555', 'tcp://*:5555' or 'tcp://0.0.0.0:5555'.

Value

Depending on 'n' specified:

  • integer: integer change in number of daemons (created or destroyed).

  • 'view': integer number of currently set daemons.

Calling daemons() without any arguments returns the 'nanoSocket' for connecting to the daemons, or NULL if it is yet to be created.

Details

Set 'n' to 0 to reset all daemon connections. {mirai} will revert to the default behaviour of creating a new background process for each request.

Specifying '.url' without 'n' assumes a value for 'n' of 1. After setting '.url', further calls specifying 'n' can be used to update the number of connected daemons (this is not strictly necessary as daemons are detected automatically, but will ensure that the correct number of shutdown signals are sent when the session is ended).

Setting a new '.url' value will attempt to shutdown existing daemons connected at the existing address before opening a connection at the new address.

About

Daemons provide a potentially more efficient solution for asynchronous operations as new processes no longer need to be created on an ad hoc basis.

Specifying '.url' allows tasks to be distributed across the network. The network topology is such that server daemons (started with server) dial into the client, which listens at the '.url' address. In this way, network resources may be added or removed at any time. The client automatically distributes tasks to all available servers.

The current implementation is low-level and ensures tasks are evenly-distributed amongst daemons without actively managing a task queue. This approach provides a robust and resource-light solution, particularly well-suited to working with similar-length tasks, or where the number of concurrent tasks typically does not exceed the number of available daemons.

Examples

if (interactive()) {
# Only run examples in interactive R sessions

# Create 2 daemons
daemons(2)
# View the number of active daemons
daemons("view")
# Reset to zero
daemons(0)

}