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Merge pull request #985 from IanCa/develop
Cache and retrieve library_data.json from hed-schemas
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"""Support utilities for hed_cache locking""" | ||
import time | ||
import os | ||
import portalocker | ||
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TIMESTAMP_FILENAME = "last_update.txt" | ||
CACHE_TIME_THRESHOLD = 300 * 6 | ||
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class CacheException(Exception): | ||
"""Exception for cache locking or threshold errors.""" | ||
pass | ||
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class CacheLock: | ||
"""Class to lock the cache folder to ensure it doesn't get hit by another version at the same time.""" | ||
def __init__(self, cache_folder, write_time=True, time_threshold=CACHE_TIME_THRESHOLD): | ||
"""Constructor for hed locking object | ||
Parameters: | ||
cache_folder(str): The folder to create the lock in(implicitly locking that folder) | ||
write_time(bool): If true, read and write the cache time. Additionally, won't operate if too recent. | ||
Generally False for local operations. | ||
time_threshold(int): Time before cache is allowed to refresh again. | ||
""" | ||
self.cache_folder = cache_folder | ||
self.cache_lock_filename = os.path.join(cache_folder, "cache_lock.lock") | ||
self.cache_lock = None | ||
self.timestamp = None | ||
self.write_time = write_time | ||
self.time_threshold = time_threshold | ||
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def __enter__(self): | ||
os.makedirs(self.cache_folder, exist_ok=True) | ||
last_timestamp = _read_last_cached_time(self.cache_folder) | ||
self.current_timestamp = time.time() | ||
time_since_update = self.current_timestamp - last_timestamp | ||
if time_since_update < self.time_threshold: | ||
raise CacheException(f"Last updated {time_since_update} seconds ago. Threshold is {self.time_threshold}") | ||
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try: | ||
self.cache_lock = portalocker.Lock(self.cache_lock_filename, timeout=1) | ||
except portalocker.exceptions.LockException: | ||
raise CacheException(f"Could not lock cache using {self.cache_lock_filename}") | ||
pass | ||
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def __exit__(self, exc_type, exc_value, traceback): | ||
if self.write_time: | ||
_write_last_cached_time(self.current_timestamp, self.cache_folder) | ||
self.cache_lock.release() | ||
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def _read_last_cached_time(cache_folder): | ||
""" Check the given cache folder to see when it was last updated. | ||
Parameters: | ||
cache_folder (str): The folder we're caching hed schema in. | ||
Returns: | ||
float: The time we last updated the cache. Zero if no update found. | ||
""" | ||
timestamp_filename = os.path.join(cache_folder, TIMESTAMP_FILENAME) | ||
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try: | ||
with open(timestamp_filename, "r") as f: | ||
timestamp = float(f.readline()) | ||
return timestamp | ||
except FileNotFoundError or ValueError or IOError: | ||
return 0 | ||
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def _write_last_cached_time(new_time, cache_folder): | ||
""" Set the time of last cache update. | ||
Parameters: | ||
new_time (float): The time this was updated. | ||
cache_folder (str): The folder used for caching the hed schema. | ||
:raises ValueError: | ||
- something went wrong writing to the file | ||
""" | ||
timestamp_filename = os.path.join(cache_folder, TIMESTAMP_FILENAME) | ||
try: | ||
with open(timestamp_filename, "w") as f: | ||
f.write(str(new_time)) | ||
except Exception: | ||
raise ValueError("Error writing timestamp to hed cache") |
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{ | ||
"": { | ||
"id_range":[10000, 39999] | ||
}, | ||
"score": { | ||
"id_range":[40000, 59999] | ||
}, | ||
"lang": { | ||
"id_range":[60000, 79999] | ||
} | ||
} |
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