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Daemons (Set Persistent Processes)

Source: R/daemons.R
daemons.Rd

Set ‘daemons’ or persistent background processes to receive mirai requests. Specify ‘n’ to create daemons on the local machine. Specify ‘url’ to receive connections from remote daemons (for distributed computing across the network). Specify ‘remote’ to optionally launch remote daemons via a remote configuration. By default, dispatcher ensures optimal scheduling.

Usage

daemons(
  n,
  url = NULL,
  remote = NULL,
  dispatcher = TRUE,
  ...,
  force = TRUE,
  seed = NULL,
  serial = NULL,
  tls = NULL,
  pass = NULL,
  .compute = "default"
)

Arguments

n

integer number of daemons to launch.

url

[default NULL] if specified, a character string comprising a URL at which to listen for remote daemons, including a port accepting incoming connections, e.g. 'tcp://hostname:5555' or 'tcp://10.75.32.70:5555'. Specify a URL with scheme 'tls+tcp://' to use secure TLS connections (for details see Distributed Computing section below). Auxiliary function host_url may be used to construct a valid host URL.

remote

[default NULL] required only for launching remote daemons, a configuration generated by remote_config or ssh_config.

dispatcher

[default TRUE] logical value, whether to use dispatcher. Dispatcher runs in a separate process to ensure optimal scheduling, although this may not always be required (for details see Dispatcher section below).

...

(optional) additional arguments passed through to daemon if launching daemons. These include ‘asyncdial’, ‘autoexit’, ‘cleanup’, ‘output’, ‘maxtasks’, ‘idletime’ and ‘walltime’.

force

[default TRUE] logical value whether to always reset daemons and apply new settings for a compute profile, even if already set. If FALSE, applying new settings requires daemons to be explicitly reset first using daemons(0).

seed

[default NULL] (optional) supply a random seed (single value, interpreted as an integer). This is used to inititalise the L'Ecuyer-CMRG RNG streams sent to each daemon. Note that reproducible results can be expected only for dispatcher = 'none', as the unpredictable timing of task completions would otherwise influence the tasks sent to each daemon. Even for dispatcher = 'none', reproducibility is not guaranteed if the order in which tasks are sent is not deterministic.

serial

[default NULL] (optional, requires dispatcher) a configuration created by serial_config to register serialization and unserialization functions for normally non-exportable reference objects, such as Arrow Tables or torch tensors.

tls

[default NULL] (optional for secure TLS connections) if not supplied, zero-configuration single-use keys and certificates are automatically generated. If supplied, either the character path to a file containing the PEM-encoded TLS certificate and associated private key (may contain additional certificates leading to a validation chain, with the TLS certificate first), or a length 2 character vector comprising [i] the TLS certificate (optionally certificate chain) and [ii] the associated private key.

pass

[default NULL] (required only if the private key supplied to ‘tls’ is encrypted with a password) For security, should be provided through a function that returns this value, rather than directly.

.compute

[default 'default'] character value for the compute profile to use (each compute profile has its own independent set of daemons).

Value

The integer number of daemons launched locally (zero if specifying ‘url’ / using a remote launcher).

Details

Use daemons(0) to reset daemon connections:

  • All connected daemons and/or dispatchers exit automatically.

  • mirai reverts to the default behaviour of creating a new background process for each request.

  • Any unresolved ‘mirai’ will return an ‘errorValue’ 19 (Connection reset) after a reset.

  • Calling daemons with revised (or even the same) settings for the same compute profile resets daemons before applying the new settings if force = TRUE.

If the host session ends, all connected dispatcher and daemon processes automatically exit as soon as their connections are dropped (unless the daemons were started with autoexit = FALSE). If a daemon is processing a task, it will exit as soon as the task is complete.

To reset persistent daemons started with autoexit = FALSE, use daemons(NULL) instead, which also sends exit signals to all connected daemons prior to resetting.

For historical reasons, daemons() with no arguments returns the value of status.

Local Daemons

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

Supply the argument ‘n’ to set the number of daemons. New background daemon processes are automatically created on the local machine connecting back to the host process, either directly or via dispatcher.

Dispatcher

By default dispatcher = TRUE launches a background process running dispatcher. Dispatcher connects to daemons on behalf of the host and ensures optimal FIFO scheduling of tasks.

Specifying dispatcher = FALSE, uses the default behaviour without additional dispatcher logic. In this case daemons connect directly to the host and tasks are distributed in a round-robin fashion. Optimal scheduling is not guaranteed as the duration of tasks cannot be known a priori, hence tasks can be queued at one daemon while other daemons remain idle. However, this provides the most resource-light approach, suited to working with similar-length tasks, or where concurrent tasks typically do not exceed available daemons.

Distributed Computing

Specifying ‘url’ as a character string allows tasks to be distributed across the network. ‘n’ is not required in this case, and disregarded if supplied.

Supply a URL with a ‘tcp://’ scheme, such as ‘tcp://10.75.32.70:5555’. The host / dispatcher listens at this address, utilising a single port. Individual daemons (started with daemon) may then dial in to this URL. Host / dispatcher automatically adjusts to the number of daemons actually connected, allowing dynamic upscaling or downscaling as required.

Switching the URL scheme to ‘tls+tcp://’ automatically upgrades the connection to use TLS. The auxiliary function host_url may be used to construct a valid host URL based on the computer's hostname.

IPv6 addresses are also supported and must be enclosed in square brackets [ ] to avoid confusion with the final colon separating the port. For example, port 5555 on the IPv6 loopback address ::1 would be specified as ‘tcp://[::1]:5555’.

Specifying the wildcard value zero for the port number e.g. ‘tcp://[::1]:0’ will automatically assign a free ephemeral port. Use status to inspect the actual assigned port at any time.

Specify ‘remote’ with a call to remote_config or ssh_config to launch daemons on remote machines. Otherwise, launch_remote may be used to generate the shell commands to deploy daemons manually on remote resources.

Compute Profiles

By default, the ‘default’ compute profile is used. Providing a character value for ‘.compute’ creates a new compute profile with the name specified. Each compute profile retains its own daemons settings, and may be operated independently of each other. Some usage examples follow:

local / remote daemons may be set with a host URL and specifying ‘.compute’ as ‘remote’, which creates a new compute profile. Subsequent mirai calls may then be sent for local computation by not specifying the ‘.compute’ argument, or for remote computation to connected daemons by specifying the ‘.compute’ argument as ‘remote’.

cpu / gpu some tasks may require access to different types of daemon, such as those with GPUs. In this case, daemons() may be called to set up host URLs for CPU-only daemons and for those with GPUs, specifying the ‘.compute’ argument as ‘cpu’ and ‘gpu’ respectively. By supplying the ‘.compute’ argument to subsequent mirai calls, tasks may be sent to either ‘cpu’ or ‘gpu’ daemons as appropriate.

Note: further actions such as resetting daemons via daemons(0) should be carried out with the desired ‘.compute’ argument specified.

Examples

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

# Create 2 local daemons (using dispatcher)
daemons(2)
status()
# Reset to zero
daemons(0)

# Create 2 local daemons (not using dispatcher)
daemons(2, dispatcher = FALSE)
status()
# Reset to zero
daemons(0)

# Set up dispatcher accepting TLS over TCP connections
daemons(url = host_url(tls = TRUE))
status()
# Reset to zero
daemons(0)

# Set host URL for remote daemons to dial into
daemons(url = host_url(), dispatcher = FALSE)
status()
# Reset to zero
daemons(0)

# Use with() to evaluate with daemons for the duration of the expression
with(
  daemons(2),
  {
    m1 <- mirai(Sys.getpid())
    m2 <- mirai(Sys.getpid())
    cat(m1[], m2[], "\n")
  }
)

}

if (FALSE) { # \dontrun{
# Launch daemons on remotes 'nodeone' and 'nodetwo' using SSH
# connecting back directly to the host URL over a TLS connection:

daemons(n = 1L,
        url = host_url(tls = TRUE),
        remote = ssh_config(c('ssh://nodeone', 'ssh://nodetwo')),
        dispatcher = FALSE)

# Launch 4 daemons on the remote machine 10.75.32.90 using SSH tunnelling
# over port 5555 ('url' hostname must be '127.0.0.1'):

daemons(n = 4L,
        url = 'tcp://127.0.0.1:5555',
        remote = ssh_config('ssh://10.75.32.90', tunnel = TRUE, port = 5555))

} # }