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December 18, 2015 02:48
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A simple LRU-based file cache, assuming that a RAM-disk is present at ~/ramdisk.
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import os, time, shutil, heapq | |
MAX_CACHE_MB = 200 | |
_CACHED_FILES = [] | |
_CACHED_SIZE = None # in bytes | |
def cache_file(filename): | |
''' | |
Automatically maintain a cached version of the given filename. | |
It assumes that there is a RAM-disk cache at ~/ramdisk, and puts the | |
cached files as the same path as in the original file system. The | |
cache size is limited (configurable) and it automatically removes | |
oldest one if the size limit is exceeded like LRU. | |
''' | |
global _CACHED_FILES, _CACHED_SIZE | |
assert os.path.isfile(filename) | |
homedir = os.environ['HOME'] | |
ramdir = os.path.join(homedir, 'ramdisk') | |
if not os.path.isdir(ramdir): | |
return filename | |
cachedir = os.path.join(ramdir, 'myscriptname') | |
if _CACHED_SIZE is None: | |
# update the current cache size when first called. | |
_CACHED_SIZE = 0 | |
for root, dirs, files in os.walk(cachedir): | |
for name in files: | |
filepath = os.path.join(root, name) | |
_CACHED_SIZE += os.path.getsize(filepath) | |
heapq.heappush(_CACHED_FILES, (os.path.getmtime(filepath), filepath)) | |
print('cache_file: Initial status: {0:.3f} MB'.format(_CACHED_SIZE / 1024 / 1024)) | |
# NOTE: we need different path split mechanism for Windows. | |
filename = os.path.abspath(filename) | |
origdir, origname = os.path.split(filename) | |
targetdir = os.path.join(cachedir, origdir[1:]) | |
cached_filename = os.path.join(targetdir, origname) | |
os.makedirs(targetdir, exist_ok=True) | |
# if the cached file does not exist or outdated, update it. | |
if not (os.path.exists(cached_filename) and | |
os.path.getmtime(cached_filename) >= os.path.getmtime(filename)): | |
add_size = os.path.getsize(filename) | |
timestamp = time.clock_gettime(time.CLOCK_REALTIME) | |
while _CACHED_SIZE + add_size > MAX_CACHE_MB * 1024 * 1024: | |
try: | |
_, old_filename = heapq.heappop(_CACHED_FILES) | |
_CACHED_SIZE -= os.path.getsize(old_filename) | |
os.unlink(old_filename) | |
except IndexError: | |
break | |
heapq.heappush(_CACHED_FILES, (timestamp, cached_filename)) | |
shutil.copyfile(filename, cached_filename) | |
_CACHED_SIZE += add_size | |
return cached_filename | |
# Example usage | |
filename = cache_file(filename) |
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