Erlang Message Sync

Erlang Message Synchronization

Provides Erlang-style message passing primitives using /tmp file system as a message transport layer.

Overview

This skill enables true message-passing semantics between simulated Erlang processes:

• Asynchronous send: Non-blocking message delivery
• Blocking receive: Waits until matching message arrives
• Pattern matching: Filter messages by sender
• Timeout support: Prevent infinite blocking
• Message persistence: Uses filesystem for reliable delivery

Message Format

Messages are stored as JSON files in /tmp/erlang-messages/<to-pid>/:

/tmp/erlang-messages/
├── main/
│   ├── worker_1-1704067200000000000.json
│   └── worker_2-1704067201000000000.json
├── worker_1/
│   └── main-1704067199000000000.json
└── coordinator/
    ├── worker_1-1704067202000000000.json
    └── worker_2-1704067203000000000.json

Quick Start

Sending a Message

Send a message from one process to another (non-blocking):

# Get the plugin installation path
PLUGIN_PATH="$HOME/.claude/plugins/marketplaces/kokuyouwind-plugins/plugins/code-like-prompt"

# Send message: main -> worker_1
bash "${PLUGIN_PATH}/skills/erlang-message-sync/scripts/send-message.sh" \
    main \
    worker_1 \
    '{"type":"request","from":"main","data":"hello"}'

Output:

Message sent from main to worker_1
Message file: /tmp/erlang-messages/worker_1/main-1704067200000000000.json
Message content: {"type":"request","from":"main","data":"hello"}

Receiving a Message

Receive a message (blocking until message arrives or timeout):

# Receive any message for worker_1 (30s timeout default)
MESSAGE=$(bash "${PLUGIN_PATH}/skills/erlang-message-sync/scripts/receive-message.sh" worker_1)
echo "Received: ${MESSAGE}"

# Receive only from 'main' with 5s timeout
MESSAGE=$(bash "${PLUGIN_PATH}/skills/erlang-message-sync/scripts/receive-message.sh" \
    worker_1 \
    main \
    5)

Output:

Waiting for message to worker_1 from main (timeout: 5s)...
Received message at worker_1 from main
Message content: {"type":"request","from":"main","data":"hello"}
{"type":"request","from":"main","data":"hello"}

Script Reference

send-message.sh

Syntax:

send-message.sh <from-pid> <to-pid> <message-json>

Arguments:

• from-pid: Sender's process identifier
• to-pid: Recipient's process identifier
• message-json: Message content as JSON string

Behavior:

• Creates mailbox directory /tmp/erlang-messages/<to-pid> if needed
• Writes message to <to-pid>/<from-pid>-<timestamp>.json
• Returns immediately (non-blocking)

Example:

bash send-message.sh coordinator worker_1 '{"task":"process","value":42}'

receive-message.sh

Syntax:

receive-message.sh <pid> [from-pid-pattern] [timeout-seconds]

Arguments:

• pid: Receiving process identifier
• from-pid-pattern (optional): Filter by sender (glob pattern, default: *)
• timeout-seconds (optional): Maximum wait time (default: 30)

Behavior:

• Polls /tmp/erlang-messages/<pid>/ every 100ms
• Blocks until matching message found or timeout
• Consumes (deletes) the message file after reading
• Returns message content to stdout
• Exits with code 1 on timeout

Examples:

# Receive any message
MESSAGE=$(bash receive-message.sh main)

# Receive only from worker_1
MESSAGE=$(bash receive-message.sh coordinator worker_1)

# Receive from worker_1 with 10s timeout
MESSAGE=$(bash receive-message.sh coordinator worker_1 10)

Usage Patterns

Request-Response Pattern

# Sender (main process)
bash send-message.sh main worker_1 '{"type":"request","data":"compute"}'
RESPONSE=$(bash receive-message.sh main worker_1 10)
echo "Got response: ${RESPONSE}"

# Receiver (worker_1 process)
REQUEST=$(bash receive-message.sh worker_1 main)
# ... process request ...
bash send-message.sh worker_1 main '{"type":"response","result":"done"}'

Multi-Process Coordination

# Main spawns two workers
bash send-message.sh main worker_1 '{"task":"A"}' &
bash send-message.sh main worker_2 '{"task":"B"}' &

# Workers send results to coordinator
# (In worker_1)
RESULT_1=$(bash receive-message.sh worker_1 main)
bash send-message.sh worker_1 coordinator '{"result":"A_done"}'

# (In worker_2)
RESULT_2=$(bash receive-message.sh worker_2 main)
bash send-message.sh worker_2 coordinator '{"result":"B_done"}'

# Coordinator collects both results
RESULT_A=$(bash receive-message.sh coordinator worker_1)
RESULT_B=$(bash receive-message.sh coordinator worker_2)
bash send-message.sh coordinator main '{"combined":"A_done,B_done"}'

Selective Receive (Pattern Matching)

# Receive only 'done' messages from any worker
MESSAGE=$(bash receive-message.sh coordinator "worker_*")

# Receive specifically from worker_1
MESSAGE=$(bash receive-message.sh coordinator worker_1)

Important Notes

Message Ordering

• Messages from the same sender arrive in send order
• Messages from different senders may be received in any order
• Use timestamps in filenames to maintain chronological order

Cleanup

Messages are automatically deleted when received. To manually clean up:

rm -rf /tmp/erlang-messages

Error Handling

• Send never fails (fire-and-forget semantics)
• Receive fails with exit code 1 on timeout
• Check exit codes when receiving:

if MESSAGE=$(bash receive-message.sh main worker_1 5); then
    echo "Received: ${MESSAGE}"
else
    echo "Timeout or error"
fi

Plugin Path Resolution

The scripts are located at:

$HOME/.claude/plugins/marketplaces/kokuyouwind-plugins/plugins/code-like-prompt/skills/erlang-message-sync/scripts/

When using in commands, always resolve the full path or set a variable:

SKILL_DIR="$HOME/.claude/plugins/marketplaces/kokuyouwind-plugins/plugins/code-like-prompt/skills/erlang-message-sync"

bash "${SKILL_DIR}/scripts/send-message.sh" main worker_1 '{"msg":"hi"}'
bash "${SKILL_DIR}/scripts/receive-message.sh" worker_1

Limitations

• Not true concurrency: Scripts run sequentially unless backgrounded with &
• Filesystem overhead: Slower than in-memory message passing
• No mailbox introspection: Can't check mailbox size without listing directory
• No message priority: FIFO order within sender
• Timeout granularity: 100ms polling interval

When to Use This Skill

Use this skill when:

• Testing Erlang-style actor model commands (08-series)
• Need actual blocking receive semantics
• Want to verify message ordering behavior
• Simulating multi-process coordination with real synchronization

Do not use when:

• Simple textual simulation is sufficient
• Performance is critical
• Running in sandboxed environment without /tmp access