threading.Thread: Add start=False parameter to start immediately the thread

[vstinner]

It's common to create multiple threads, start them, and then join them. Example:

threads = [
 threading.Thread(target=run_a),
 threading.Thread(target=run_b),
]
for thread in threads:
 thread.start()
...
for thread in threads:
 thread.join()

I propose adding a start=False parameter to threading.Thread to start immediately the thread. The example would become:

threads = [
 threading.Thread(target=run_a, start=True),
 threading.Thread(target=run_b, start=True),
]
...
for thread in threads:
 thread.join()

---

The new parameter would solve the old issue gh-93293 which requests to return self in start(). The issue example:

threads = []
for i in range(10):
 thread = threading.Thread(target=fn, args=(i,))
 thread.start()
 threads.append(thread)

for t in threads:
 t.join()

would become:

threads = [threading.Thread(target=fn, args=(i,), start=True) for i in range(10)]

for t in threads:
 t.join()

Linked PRs

• gh-155334: Add start parameter to threading.Thread #155335

[vstinner]

Adding a start parameter was mentioned in https://discuss.python.org/t/add-a-threading-run-convenience-function/108430 discussion.

[ZeroIntensity]

I think threading.run/threading.run_daemon would be better, because the ergonomics of group (see #155348), args, and kwargs are bad. Constructors should also generally not perform expensive operations.