Skip to content

PID_TRACKING_IN_LINUX.md

Latest commit

 

History

History
109 lines (82 loc) · 3.5 KB

PID_TRACKING_IN_LINUX.md

File metadata and controls

109 lines (82 loc) · 3.5 KB

Shell Script PID Tracking Solution for AYON

Problem

When launching applications through shell scripts on Linux, the process ID returned by the app_launcher (mid-process) corresponds to the shell process, not the actual application process that the shell script launches.

Architecture Overview

  • AYON Applications Manager (manager.py) creates launch contexts and manages application processes
  • App Launcher (app_launcher.py/app_launcher.cpp in ayon-launcher) is the mid-process that handles detached process launching on Linux
  • Shell Scripts are often used as executables that set up environment and launch actual applications

Solution

The solution implements a PID file convention that allows shell scripts to communicate the actual application PID back to AYON through the app_launcher mid-process.

How it Works

  1. PID File Creation: The AYON manager creates a temporary PID file and provides its path to the app_launcher via JSON data
  2. Environment Variable: The app_launcher passes the PID file path to shell scripts via AYON_PID_FILE environment variable
  3. Shell Script Responsibility: Shell scripts can write the actual application PID to this file after launching the application
  4. PID Discovery: The app_launcher waits briefly and checks for an updated PID in the file, using it if found

Shell Script Implementation Examples

Bash Example

#!/bin/bash

# Launch the actual application in background
/path/to/actual/application "$@" &

# Get the PID of the actual application
APP_PID=$!

# Write the PID to the AYON PID file if available
if [ -n "$AYON_PID_FILE" ]; then
    echo "$APP_PID" > "$AYON_PID_FILE"
fi

# Wait for the application to finish (optional)
wait $APP_PID

Python Launcher Example

#!/usr/bin/env python3
import os
import subprocess
import sys

# Launch the actual application
process = subprocess.Popen(["/path/to/actual/application"] + sys.argv[1:])

# Write the PID to the AYON PID file if available
pid_file = os.environ.get("AYON_PID_FILE")
if pid_file:
    try:
        with open(pid_file, "w") as f:
            f.write(str(process.pid))
    except OSError:
        pass  # Ignore if we can't write to the file

# Wait for the application to finish
process.wait()
sys.exit(process.returncode)

Complex Shell Script Example

#!/bin/bash

# Set up environment
export SOME_APP_PATH="/opt/myapp"
export LD_LIBRARY_PATH="$SOME_APP_PATH/lib:$LD_LIBRARY_PATH"

# Change to application directory
cd "$SOME_APP_PATH"

# Launch the actual application with custom arguments
./myapp --custom-flag --config=/path/to/config "$@" &

# Capture the actual application PID
ACTUAL_PID=$!

# Communicate the PID back to AYON if PID file is available
if [ -n "$AYON_PID_FILE" ]; then
    echo "$ACTUAL_PID" > "$AYON_PID_FILE"
    echo "Wrote actual application PID $ACTUAL_PID to $AYON_PID_FILE"
fi

# Wait for the application
wait $ACTUAL_PID
EXIT_CODE=$?

# Cleanup if needed
cleanup_function

exit $EXIT_CODE

Environment Variables Available to Shell Scripts

AYON_PID_FILE: Path to the file where the actual application PID should be written

Integration Requirements

For shell scripts to take advantage of this feature:

  1. Check if $AYON_PID_FILE environment variable exists
  2. Launch your application in the background using &
  3. Capture the PID using $! (bash) or equivalent
  4. Write the PID to the file specified by $AYON_PID_FILE
  5. Optionally wait for the application to complete
⚡