mirai - Quick Reference

Core Concepts

mirai = future in Japanese. Async evaluation framework for R built on NNG/nanonext.

Architecture: daemons dial into host, a topology which facilitates dynamic scaling.

This is a cheatsheet. Refer to the mirai reference manual for a detailed introduction.

Key Takeaways

• mirai() returns immediately, access result via m[] or m$data
• daemons() sets persistent background processes
• Dispatcher enabled by default for optimal scheduling
• SSH tunnelling: Use local_url(tcp=TRUE) + tunnel=TRUE when ports blocked
• HPC clusters: Use cluster_config() with appropriate scheduler
• Compute profiles: Multiple independent daemon sets with .compute parameter
• mirai_map(): Parallel map with progress bars, early stopping, flatmap

1. Basic mirai Usage

Create and Access Results

library(mirai)

# Create a mirai (returns immediately)
m <- mirai(
  {
    Sys.sleep(1)
    rnorm(5, mean)
  },
  mean = 10
)

# Direct access (non-blocking)
unresolved(m)              # Check if resolved (TRUE if still running)
m$data                     # Returns value (NA if unresolved)

# Access result (blocks until ready)
m[]                        # Wait and return value
collect_mirai(m)           # Wait and return value
call_mirai(m)              # Wait and return mirai object

Passing Data

# Via ... (assigned to daemon global env)
m <- mirai(func(x), func = my_func, x = data)

# Via .args (local to evaluation env)
m <- mirai(func(x), .args = list(func = my_func, x = data))

# Pass entire environment
write_async <- function(x, file) {
  mirai(write.csv(x, file), .args = environment())
}

2. Local Daemons

Basic Setup

# Set 4 local daemons (with dispatcher - default)
daemons(4)

# Without dispatcher (round-robin distribution)
daemons(4, dispatcher = FALSE)

# Reset daemons
daemons(0)

# Check connection / statistics
info()

Daemon Configuration

daemons(
  n = 4,
  dispatcher = TRUE,          # Use dispatcher for optimal FIFO scheduling
  cleanup = TRUE,             # Clean env between tasks
  output = FALSE,             # Capture stdout/stderr
  maxtasks = Inf,             # Task limit per daemon
  idletime = Inf,             # Max idle time (ms) before exit
  walltime = Inf              # Time limit (ms) before exit
)

Synchronous Mode (Testing/Debugging)

daemons(sync = TRUE)          # Run in current process
m <- mirai(Sys.getpid())
daemons(0)

3. Remote Daemons - SSH Direct

Setup Host to Accept Remote Connections

# Listen at host URL with TLS
daemons(
  url = host_url(tls = TRUE),
  remote = ssh_config(c("ssh://10.75.32.90", "ssh://node2:22"))
)

# Or without automatic launching
daemons(url = host_url(tls = TRUE))
launch_remote(2, remote = ssh_config("ssh://10.75.32.90"))

URL Constructors

host_url()                    # Auto-detect IP, tcp://x.x.x.x:0
host_url(tls = TRUE)          # TLS connection
host_url(tls = TRUE, port = 5555)  # Specific port

local_url()                   # IPC (Unix sockets/named pipes)
local_url(tcp = TRUE)         # tcp://127.0.0.1:0
local_url(tcp = TRUE, port = 5555) # tcp://127.0.0.1:5555

SSH Configuration

ssh_config(
  remotes = c("ssh://node1:22", "ssh://node2:22"),
  tunnel = FALSE,             # Direct connection
  timeout = 10,               # Connection timeout (seconds)
  command = "ssh",            # SSH executable
  rscript = "Rscript"         # R executable on remote
)

Requirements for SSH Direct:

• SSH key-based authentication in place
• Host port open to inbound connections from remote
• Remotes dial back to host URL directly

4. Remote Daemons - SSH Tunnelling

When to Use Tunnelling

• Firewall blocks inbound connections to host
• Security policies prevent opening ports
• Connecting to cloud/external machines

Setup

# Host uses localhost URL
daemons(
  n = 4,
  url = local_url(tcp = TRUE),              # tcp://127.0.0.1:0
  remote = ssh_config("ssh://10.75.32.90", tunnel = TRUE)
)

# Or with specific port
daemons(
  n = 2,
  url = local_url(tcp = TRUE, port = 5555), # tcp://127.0.0.1:5555
  remote = ssh_config("ssh://remote-server", tunnel = TRUE)
)

How Tunnelling Works:

1. Host listens on 127.0.0.1:port
2. SSH creates reverse tunnel: remote port -> host port
3. Remote daemons dial into their own 127.0.0.1:port
4. Traffic tunnels back through SSH connection

5. HPC Cluster Configurations

General Pattern

daemons(
  n = 4,
  url = host_url(),
  remote = cluster_config(
    command = "sbatch",  # Scheduler command: "sbatch", "qsub", "bsub", etc.
    options = "#SBATCH --job-name=mirai
               #SBATCH --mem=16G
               #SBATCH --cpus-per-task=1
               #SBATCH --output=mirai_%j.out
               #SBATCH --error=mirai_%j.err
               module load R/4.5.0",
    rscript = file.path(R.home("bin"), "Rscript")
  )
)

Scheduler-Specific Directives

Scheduler	Command	Job Name	Memory	CPUs
Slurm	sbatch	#SBATCH --job-name=NAME	--mem=16G	--cpus-per-task=1
SGE	qsub	#$ -N NAME	-l mem_free=16G	-pe smp 1
Torque/PBS	qsub	#PBS -N NAME	-l mem=16gb	-l nodes=1:ppn=1
LSF	bsub	#BSUB -J NAME	-M 16000	-n 1

6. Manual Daemon Deployment

Generate Launch Commands

# Set daemons to listen
daemons(url = host_url(tls = TRUE))

# Get launch commands (doesn't execute)
cmds <- launch_remote(
  n = 2,
  remote = remote_config()  # Empty config returns commands
)

# Copy/paste commands to run on remote machines
# E.g. Rscript -e "mirai::daemon('tcp://10.75.32.70:5555')"
print(cmds)

7. Compute Profiles

Multiple Independent Profiles

# Create CPU profile
daemons(4, .compute = "cpu")

# Create GPU profile
daemons(2, .compute = "gpu")

# Direct tasks to specific profile
m_cpu <- mirai(heavy_compute(), .compute = "cpu")
m_gpu <- mirai(gpu_task(), .compute = "gpu")

# Reset specific profile
daemons(0, .compute = "cpu")

Scoped Profiles

# Temporarily use profile
with_daemons("gpu", {
  model <- mirai(train_model())
})

# Set profile for scope
local_daemons("cpu")
m <- mirai(task())  # Uses "cpu" profile

8. Common Patterns

Temporary Daemons

with(daemons(4), {
  m1 <- mirai(task1())
  m2 <- mirai(task2())
  c(m1[], m2[])
})
# Daemons auto-reset on exit

Mixed Local/Remote Resources

daemons(url = host_url())
launch_local(2)             # 2 local daemons
launch_remote(4, ssh_config("ssh://remote"))  # 4 remote

Dynamic Scaling

daemons(url = host_url())   # Start listening
launch_local(2)   # Add 2 daemons
# Later...
# Add 2 more (automatically exit after idle for 60 secs)
launch_local(2, idletime = 60000)

9. mirai_map - Parallel Map

Basic Usage

daemons(4)

# Simple map
results <- mirai_map(1:10, sqrt)[]

# With additional arguments
results <- mirai_map(
  1:10,
  rnorm,
  .args = list(mean = 5, sd = 2)
)[]

# With helper functions
results <- mirai_map(
  1:100,
  function(x) transform(x, helper),
  helper = my_helper_func
)[]

Collection Options

# Flatten to vector
results <- mirai_map(1:10, rnorm, .args = list(n = 1))[.flat]

# Progress bar
results <- mirai_map(1:100, slow_func)[.progress]

# Early stopping on error
results <- mirai_map(data_list, process)[.stop]

# Combine options
results <- mirai_map(1:100, task)[.stop, .progress]

Multiple Map (over DataFrame/Matrix)

# Map over dataframe rows
df <- data.frame(x = 1:10, y = 11:20)
mirai_map(df, function(x, y) x + y)[.flat]

# Map over matrix rows
mat <- matrix(1:6, nrow = 3, dimnames = list(c("a","b","c"), c("x","y")))
mirai_map(mat, function(x, y) x * y)[]

10. Error Handling

m <- mirai(stop("error"))
m[]

# Test error types
is_mirai_error(m$data)      # Execution error
is_mirai_interrupt(m$data)  # User interrupt
is_error_value(m$data)      # Any error (catch-all)

# Access error details
m$data$stack.trace          # Full stack trace
m$data$condition.class      # Original error classes
m$data$message              # Error message

11. Monitoring and Status

status()                    # Detailed status
info()                      # Concise statistics

daemons_set()               # Check if daemons exist
require_daemons()           # Error if not set

12. Advanced Features

Timeouts

# Per-mirai timeout (requires dispatcher for auto-cancellation)
m <- mirai(Sys.sleep(10), .timeout = 1000)  # 1 second
m[]  # Returns errorValue 5 (timed out)

Cancellation

# Cancel mirai (requires dispatcher)
m <- mirai(Sys.sleep(100))
stop_mirai(m)  # Attempts cancellation
m$data         # errorValue 20 (canceled)

Evaluation Everywhere

# Load package on all daemons
everywhere(library(data.table))

# Export variables to all daemons
everywhere(config <<- list(threads = 4))

# Export variables to all daemons
everywhere({}, db_conn = my_conn, api_key = key)

Random Seeds (Reproducible)

# Statistically-sound but non-reproducible (default)
daemons(4, seed = NULL)

# Reproducible RNG (seed per mirai call)
daemons(4, seed = 123)

Custom Serialization

# For torch tensors, Arrow tables, Polars objects
daemons(
  4,
  serial = serial_config(
    "torch_tensor",
    sfunc = torch::torch_serialize,
    ufunc = torch::torch_load
  )
)

# Global registration
register_serial("torch_tensor", torch::torch_serialize, torch::torch_load)
daemons(4)  # Auto-applies registered configs

TLS Configuration

# Auto TLS (zero-config certificates)
daemons(url = host_url(tls = TRUE))

# Custom certificate
daemons(
  url = host_url(tls = TRUE),
  tls = "/path/to/cert.pem",
  pass = function() askpass::askpass()
)

13. Dispatcher vs. Direct

Feature	With Dispatcher (default)	Direct (dispatcher=FALSE)
Scheduling	Optimal FIFO	Round-robin
Timeouts	✓	No auto-cancellation
Cancellation	✓	✗
Serialization	✓	✗
Overhead	Slightly higher	Minimal
Use case	Variable task times	Similar task times

14. Quick Decision Tree

┌─ Need async in R?
│
├─ Single task → mirai()
│  └─ No daemons set? → ephemeral (auto-creates process)
│
├─ Map operation → mirai_map()
│  └─ Requires daemons() to be set first
│
└─ Multiple tasks → Set up daemons
   │
   ├─ Local only
   │  └─ daemons(n)
   │
   ├─ Remote with open ports
   │  └─ daemons(url = host_url(), remote = ssh_config(..., tunnel = FALSE))
   │
   ├─ Remote with firewall/blocked ports
   │  └─ daemons(url = local_url(tcp = TRUE), remote = ssh_config(..., tunnel = TRUE))
   │
   └─ HPC cluster (Slurm/SGE/PBS/LSF)
      └─ daemons(url = host_url(), remote = cluster_config(...))

15. Common Gotchas

# Expression Evaluation
mirai(pkg::func(x), x = data)
# Namespace functions OR library() inside expression
mirai(func(x), func = my_func, x = data)
# Pass dependencies explicitly via ... or .args

# Dispatcher Required For
stop_mirai(m)                           # Cancellation
mirai(task(), .timeout = 1000)          # Timeout cancellation
daemons(4, serial = serial_config(...)) # Custom serialization

# SSH Tunnelling
daemons(url = local_url(tcp = TRUE), remote = ssh_config(..., tunnel = TRUE))
# Must use 127.0.0.1 (not external IP) + tunnel = TRUE

# TLS
host_url(tls = TRUE)                    # Auto TLS (zero-config, just works)
# Custom certs: provide cert path + optional passphrase function

# Remote Prerequisites
# - SSH key-based auth configured beforehand
# - SSH direct: host port open to inbound connections
# - HPC: correct module load commands and scheduler directives