clean-unused-caches: Optimize performance.

This saves about 400ms when running clean-unused-caches, basically by
calling its sub-rountines by import (rather than
`subprocess.check_call()`).  The performance optimization seems well worth it.

Fixes #9766.

docs/subsystems/dependencies.md

@@ -164,7 +164,7 @@ highlighting.  The system is largely managed by the code in
   finally, we use `pip`'s built-in caching to ensure that a specific
   version of a specific package is only downloaded once.
 * **Garbage-collecting caches**.  We have a tool,
-  `scripts/lib/clean-venv-cache`, which will clean old cached
+  `scripts/lib/clean_venv_cache.py`, which will clean old cached
   virtualenvs that are no longer in use.  In production, the algorithm
   preserves recent virtualenvs as well as those in use by any current
   production deployment directory under `/home/zulip/deployments/`.
@@ -188,7 +188,7 @@ reasoning here.
   `scripts/lib/node_cache.py` manages cached `node_modules`
   directories in `/srv/zulip-npm-cache`.  Each is named by its hash,
   computed by the `generate_sha1sum_node_modules` function.
-  `scripts/lib/clean-npm-cache` handles garbage-collection.
+  `scripts/lib/clean_node_cache.py` handles garbage-collection.
 * We use [yarn][], a `pip`-like tool for JavaScript, to download most
   JavaScript dependencies.  Yarn talks to standard the [npm][]
   repository.  We use the standard `package.json` file to declare our
@@ -248,7 +248,7 @@ environments where they need to be displayed.
 Since processing emoji is a relatively expensive operation, as part of
 optimizing provisioning, we use the same caching strategy for the
 compiled emoji data as we use for virtualenvs and `node_modules`
-directories, with `scripts/lib/clean-emoji-cache` responsible for
+directories, with `scripts/lib/clean_emoji_cache.py` responsible for
 garbage-collection.  This caching and garbage-collection is required
 because a correct emoji implementation involves over 1000 small image
 files and a few large ones.  There is a more extended article on our

scripts/lib/clean-unused-caches

@@ -7,14 +7,15 @@ import sys
 ZULIP_PATH = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 sys.path.append(ZULIP_PATH)
 from scripts.lib.zulip_tools import get_environment, parse_cache_script_args
+from scripts.lib import clean_venv_cache, clean_node_cache, clean_emoji_cache
 
 def main():
     # type: () -> None
-    parse_cache_script_args("This script cleans unused zulip caches.")
+    args = parse_cache_script_args("This script cleans unused zulip caches.")
     os.chdir(ZULIP_PATH)
-    subprocess.check_call(["./scripts/lib/clean-venv-cache"] + sys.argv[1:])
-    subprocess.check_call(["./scripts/lib/clean-npm-cache"] + sys.argv[1:])
-    subprocess.check_call(["./scripts/lib/clean-emoji-cache"] + sys.argv[1:])
+    clean_venv_cache.main(args)
+    clean_node_cache.main(args)
+    clean_emoji_cache.main(args)
 
 if __name__ == "__main__":
     main()

scripts/lib/clean_emoji_cache.py

@@ -38,12 +38,11 @@ def get_caches_in_use(threshold_days):
         caches_in_use.add(os.readlink(emoji_link_path))
     return caches_in_use
 
-def main():
-    # type: () -> None
-    args = parse_cache_script_args("This script cleans unused zulip emoji caches.")
+def main(args: argparse.Namespace) -> None:
     caches_in_use = get_caches_in_use(args.threshold_days)
     purge_unused_caches(
         EMOJI_CACHE_PATH, caches_in_use, "emoji cache", args)
 
 if __name__ == "__main__":
-    main()
+    args = parse_cache_script_args("This script cleans unused zulip emoji caches.")
+    main(args)

scripts/lib/clean_node_cache.py

@@ -49,12 +49,11 @@ def get_caches_in_use(threshold_days):
 
     return caches_in_use
 
-def main():
-    # type: () -> None
-    args = parse_cache_script_args("This script cleans unused zulip npm caches.")
+def main(args: argparse.Namespace) -> None:
     caches_in_use = get_caches_in_use(args.threshold_days)
     purge_unused_caches(
         NODE_MODULES_CACHE_PATH, caches_in_use, "node modules cache", args)
 
 if __name__ == "__main__":
-    main()
+    args = parse_cache_script_args("This script cleans unused zulip npm caches.")
+    main(args)

scripts/lib/clean_venv_cache.py

@@ -51,12 +51,11 @@ def get_caches_in_use(threshold_days):
 
     return caches_in_use
 
-def main():
-    # type: () -> None
-    args = parse_cache_script_args("This script cleans unused zulip venv caches.")
+def main(args: argparse.Namespace) -> None:
     caches_in_use = get_caches_in_use(args.threshold_days)
     purge_unused_caches(
         VENV_CACHE_DIR, caches_in_use, "venv cache", args)
 
 if __name__ == "__main__":
-    main()
+    args = parse_cache_script_args("This script cleans unused zulip venv caches.")
+    main(args)