Monitor Subprocess Output With Timeout

Monitor Subprocess Output With Timeout | Generated by AI

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import subprocess
import threading
import queue
import time
import sys

def read_output(proc, output_queue):
    """Thread function to read stdout and stderr, put into queue."""
    try:
        for line in iter(proc.stdout.readline, b''):
            if not line:
                break
            output_queue.put(line.decode('utf-8', errors='ignore').rstrip())
        # Also check stderr if needed
        for line in iter(proc.stderr.readline, b''):
            if not line:
                break
            output_queue.put(line.decode('utf-8', errors='ignore').rstrip())
    except Exception as e:
        output_queue.put(f"Error reading output: {e}")

def main():
    # Command to run (e.g., 'mvn clean compile' on Windows)
    cmd = ['mvn', 'clean', 'compile']  # Adjust as needed, e.g., ['cmd', '/c', 'mvn build']
    timeout_seconds = 10

    # Start the subprocess
    proc = subprocess.Popen(
        cmd,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
        bufsize=1,  # Line buffered
        universal_newlines=False,  # Handle bytes
        cwd=None  # Set working directory if needed
    )

    # Queue for output
    output_queue = queue.Queue()

    # Start thread to read output
    output_thread = threading.Thread(target=read_output, args=(proc, output_queue))
    output_thread.daemon = True
    output_thread.start()

    print("Started command. Monitoring for output every 10 seconds...")

    while proc.poll() is None:
        try:
            # Wait for output with timeout
            output = output_queue.get(timeout=timeout_seconds)
            print(f"Output: {output}")  # Optional: print or process output
        except queue.Empty:
            print(f"No output for {timeout_seconds} seconds. Terminating command and exiting.")
            proc.terminate()  # or proc.kill() for forceful kill
            try:
                proc.wait(timeout=5)  # Wait a bit for graceful shutdown
            except subprocess.TimeoutExpired:
                proc.kill()
            sys.exit(1)

    # Process has finished normally
    print("Command completed.")
    output_thread.join()  # Wait for output thread to finish

if __name__ == "__main__":
    main()

Explanation

Subprocess: Uses subprocess.Popen to run mvn clean compile (adjust the command as needed; for simple mvn build, it might be ['mvn', 'build'] or wrapped in cmd /c if needed). It’s run asynchronously with pipes for stdout and stderr.
Queue Threading: A separate thread reads from stdout and stderr line by line (to avoid reading entire output at once), decodes it, and puts lines into a queue.Queue. This allows non-blocking reads.
Timeout Monitoring: In the main thread, check the queue for new output with get(timeout=10). If no output arrives in 10 seconds, terminate the subprocess and exit.
Windows Compatibility: subprocess works on Windows. If the command requires a shell (e.g., for mvn if not in PATH), you could set shell=True and pass the command as a string: proc = subprocess.Popen("mvn clean compile", shell=True, ...).
Edge Cases: If the process exits normally while waiting, the loop stops and we join the thread. The thread is daemonic to avoid hanging on exit.
Customization: You can modify to process outputs differently (e.g., log to file instead of print). For stderr, it’s combined into the same queue; you could separate if needed. If outputs are binary, adjust decoding.

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