vscode-python: Add support to retry attaching within a specific timeout

Summary

• Basically the debugger is launched before the preLaunch script completes. Hence the debugger fails (as the process has not started and socketserver is not listening).
• Suggestion: Retry attaching to the socket with a default timeout period.
• Note; This is not a bug, but a work around for the preLaunchScripts returning even before the script has actually completed (i.e. work around for docker extension issues).

Environment data

• VS Code version: 1.38
• Extension version: 2019.9.34911
• OS and version: Windows 10, 1903
• Python version: 3.7.2

Steps to reproduce:

1. Create a Python file, e.g. myApp.py within a workspace folder
2. Create a task in tasks.json to launch that file in PTVSD in a Docker container (see below for full tasks.json), e.g. with: docker run -dt -v C:\Users\brandonw\.vscode\extensions\ms-python.python-2019.9.34911\pythonFiles:/pydbg -v ${workspaceFolder}:/app -w /app -p 5678:5678 --entrypoint python python:alpine /pydbg/ptvsd_launcher.py --default --host 0.0.0.0 --port 5678 --wait myApp.py
3. Set that task as the preLaunchTask for a Python remote attach launch config (see below for full launch.json)
4. F5

Expected behaviour

Attach works if preLaunchTask is used to start a waiting debug server with ptvsd

Actual behaviour

Attach does not work. No error is shown, it appears like debugging starts and immediately stops. If you comment out the preLaunchTask in launch.json, and then manually run the task with Ctrl + Shift + P > Run Task, it will start the container. If you then F5 it attaches successfully. I’ve also tried putting a dummy task containing a 2-second sleep inbetween, and this also works. So it seems to just be a race condition.

Logs

Nothing is output in Python output window, nor in Developer Tools console window.

Workspace

.vscode/launch.json:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Python: Remote Attach",
            "type": "python",
            "request": "attach",
            "port": 5678,
            "host": "localhost",
            "pathMappings": [
                {
                    "localRoot": "${workspaceFolder}",
                    "remoteRoot": "."
                }
            ],
            "preLaunchTask": "Docker start",
            "postDebugTask": "Docker remove"
        }
    ]
}

.vscode/tasks.json (note, you’ll need to change the C:\users\brandonw.…\pythonFiles:/pydbg path):

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "Docker start",
            "type": "shell",
            "command": "docker run -dt -v C:\\Users\\brandonw\\.vscode\\extensions\\ms-python.python-2019.9.34911\\pythonFiles:/pydbg -v ${workspaceFolder}:/app -w /app -p 5678:5678 --name myPythonApp --entrypoint python python:alpine /pydbg/ptvsd_launcher.py --default --host 0.0.0.0 --port 5678 --wait myApp.py",
            "problemMatcher": []
        },
        {
            "label": "Docker remove",
            "type": "shell",
            "command": "docker rm -f myPythonApp"
        }
    ]
}

myApp.py:

print("Hello world!")

print("Farewell!")