error RuntimeError: Set changed size during iteration

[zukka77]

Describe the bug

Launching a job to retrieve files on 715 host gives this error:

 RuntimeError: Set changed size during iteration
[snip].venv/lib/python3.13/site-packages/pyinfra_cli/util.py", line 221, in _parallel_load_hosts
    state.pool.spawn(load_file, host): host for host in state.inventory.iter_active_hosts()

To Reproduce

I'm using ssh connector on 715 hosts (not all hosts are reachable) , the inventory is dynamic:
from my_password import password

def make_hosts():
    with open("hostlist.csv", "r") as f:
        hosts = list(map(lambda x: x.strip().lower(), f.readlines()))
    return {
        "hosts": (
            hosts,
            {
                "ssh_user": "user",
                "ssh_password": password,
                "ssh_allow_agent": False,
                "ssh_known_hosts_file": "/dev/null",
                "_parallel": 10,
                "_sudo": True,
            },
        )
    }

I've tried with or without _parallel
these are the operations:

from pyinfra import host
from pyinfra.facts import server, files as files_facts
from pyinfra.operations import files
from pathlib import Path

hostname: str = host.get_fact(server.Hostname)
output_path = Path(f"sudoers/{hostname}")
(output_path / "sudoers.d").mkdir(parents=True, exist_ok=True)

files.get(
    src="/etc/sudoers",
    dest=f"sudoers/{hostname}/sudoers",
)

sudoers_d = host.get_fact(
    files_facts.FindFiles,
    "/etc/sudoers.d",
    quote_path=True,
)

for f in sudoers_d:
    files.get(
        src=f,
        dest=f"sudoers/{hostname}/sudoers.d/{Path(f).name}",
    )

Expected behavior

I'd like to have the files on my machine 😄

Meta

• Include output of pyinfra --support.
  System: Linux
  Platform: Linux-6.17.7-arch1-1-x86_64-with-glibc2.42
  Release: 6.17.7-arch1-1
  Machine: x86_64
  pyinfra: v3.5.1
  click: v8.3.0
  distro: v1.9.0
  gevent: v25.9.1
  jinja2: v3.1.6
  packaging: v25.0
  paramiko: v3.5.1
  python-dateutil: v2.9.0.post0
  typeguard: v4.4.4
  typing-extensions: v4.15.0
  Executable: [snip]/.venv/bin/pyinfra
  Python: 3.13.2 (CPython, Clang 19.1.6 )

• How was pyinfra installed (source/pip)?
  uv pip

• Include pyinfra-debug.log (if one was created)

File " [snip]/.venv/lib/python3.13/site-packages/pyinfra_cli/cli.py", line 243, in cli
    _main(*args, **kwargs)
    ~~~~~^^^^^^^^^^^^^^^^^
  File " [snip]/.venv/lib/python3.13/site-packages/pyinfra_cli/cli.py", line 378, in _main
    can_diff, state, config = _handle_commands(
                              ~~~~~~~~~~~~~~~~^
        state, config, command, original_operations, operations
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File " [snip]/.venv/lib/python3.13/site-packages/pyinfra_cli/cli.py", line 705, in _handle_commands
    state, config, operations = _prepare_deploy_operations(state, config, operations)
                                ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File " [snip]/.venv/lib/python3.13/site-packages/pyinfra_cli/cli.py", line 766, in _prepare_deploy_operations
    load_deploy_file(state, filename)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File " [snip]/.venv/lib/python3.13/site-packages/pyinfra_cli/util.py", line 235, in load_deploy_file
    _parallel_load_hosts(state, lambda: exec_file(filename), filename)
    ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File " [snip]/.venv/lib/python3.13/site-packages/pyinfra_cli/util.py", line 221, in _parallel_load_hosts
    state.pool.spawn(load_file, host): host for host in state.inventory.iter_active_hosts()
                                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
RuntimeError: Set changed size during iteration

• Consider including output with -vv and --debug.
  no other relevant informations seems added