Incorrect frame for breakpoint

[huguesv]

Environment data

• PTVSD version: today's master
• OS and version: Win10
• Python version (& distribution if applicable, e.g. Anaconda): 3.6
• Using VS Code or Visual Studio: Visual Studio

Steps to reproduce:

1. Type this code and set breakpoint on line 9 as in the picture and start debugging.

import threading
from queue import Queue
import time

print_lock = threading.Lock()

def get_url(current_url):

    time.sleep(2)
    with print_lock:
        print("\nStarting thread {}".format(threading.current_thread().name))

def process_queue():
    while True:
        current_url = url_queue.get()
        get_url(current_url)
        url_queue.task_done()

url_queue = Queue()

url_list = ["https://www.google.com"]*5

for i in range(5):
    t = threading.Thread(target=process_queue)
    t.daemon = True
    t.start()

start = time.time()

for current_url in url_list:
    url_queue.put(current_url)

url_queue.join()

Actual behavior

VS breaks on line 16.

Expected behavior

VS breaks on line 9.

[karthiknadig]

This looks like it is paused on the wrong thread. VS UI shows the last paused thread instead of the thread that hit break point. We could probably use preserveFocusHint to control that.

if the stop reason is breakpoint or exception then preserveFocusHint should be false, and it should be true for all other cases.

[karthiknadig]

@DonJayamanne Can you look at this change karthiknadig@cf7a5f6 ? Basically VS has special requirements about stopped Event.
see: https://github.com/Microsoft/VSDebugAdapterHost/wiki/Differences-between-Visual-Studio-Code-and-the-Visual-Studio-Debug-Adapter-Host#stopped-event

There is a bit more to it. we have to send stopped event if the reason in ['breakpoint', 'exception', 'step'] events, even if we sent a stopped event with reason == 'pause' otherwise VS has no clue which stack to show.