import anyio
import pytest
from pydantic import AnyUrl
from mcp.server.fastmcp import FastMCP
from mcp.shared.memory import (
create_connected_server_and_client_session as create_session,
)
_sleep_time_seconds = 0.01
_resource_name = "slow://slow_resource"
@pytest.mark.anyio
async def test_messages_are_executed_concurrently():
server = FastMCP("test")
call_timestamps = []
@server.tool("sleep")
async def sleep_tool():
call_timestamps.append(("tool_start_time", anyio.current_time()))
await anyio.sleep(_sleep_time_seconds)
call_timestamps.append(("tool_end_time", anyio.current_time()))
return "done"
@server.resource(_resource_name)
async def slow_resource():
call_timestamps.append(("resource_start_time", anyio.current_time()))
await anyio.sleep(_sleep_time_seconds)
call_timestamps.append(("resource_end_time", anyio.current_time()))
return "slow"
async with create_session(server._mcp_server) as client_session:
async with anyio.create_task_group() as tg:
for _ in range(10):
tg.start_soon(client_session.call_tool, "sleep")
tg.start_soon(client_session.read_resource, AnyUrl(_resource_name))
active_calls = 0
max_concurrent_calls = 0
for call_type, _ in sorted(call_timestamps, key=lambda x: x[1]):
if "start" in call_type:
active_calls += 1
max_concurrent_calls = max(max_concurrent_calls, active_calls)
else:
active_calls -= 1
print(f"Max concurrent calls: {max_concurrent_calls}")
assert max_concurrent_calls > 1, "No concurrent calls were executed"
def main():
anyio.run(test_messages_are_executed_concurrently)
if __name__ == "__main__":
import logging
logging.basicConfig(level=logging.DEBUG)
main()
