This algorithm synchronously checks a resource file by ensuing a lock file doesn't already exist.

algorithm_with_lock.py

from Algorithmia import ADK
import Algorithmia
from time import sleep, time

state_file_path = "data://.my/locking/resource.json"
lock_file_path = "data://.my/locking/lock"
client = Algorithmia.client()


class AlgorithmiaLock(object):
    def __init__(self, file_path, client):
        self.lock = None
        self.filepath = file_path
        self.client = client

    def __enter__(self):
        self.lock_trap()

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.lock.delete()
        self.lock = None

    def lock_trap(self):
        lock_file = self.client.file(self.filepath)
        while True:
            if lock_file.exists():
                sleep(0.5)
            else:
                break
        lock_file.putJson({})
        self.lock = lock_file


def apply(input):
    with AlgorithmiaLock(lock_file_path, client):
        state_file = client.file(state_file_path)
        if state_file.exists():
            state_data = client.file(state_file_path).getJson()
        else:
            state_data = {"count": 0, "time": None}
        state_data['count'] += 1
        state_data['time'] = str(time())
        client.file(state_file_path).putJson(state_data)
    # This sleep is to replicate business logic processing on the data recieved.
    sleep(1)
    return state_data