Enable manual garbage collection (deb-pkg-tools --garbage-collect)

deb_pkg_tools/cache.py

@@ -1,7 +1,7 @@
 # Debian packaging tools: Caching of package metadata.
 #
 # Author: Peter Odding <peter@peterodding.com>
-# Last Change: November 23, 2016
+# Last Change: November 24, 2016
 # URL: https://github.com/xolox/python-deb-pkg-tools
 
 """
@@ -154,8 +154,9 @@ def collect_garbage(self, force=False, interval=60 * 60 * 24):
         :param force: :data:`True` to force a full garbage collection run
                       (defaults to :data:`False` which means garbage collection
                       is performed only once per `interval`).
-        :param interval: Delay garbage collection so that it's performed only
-                         once per given interval (the number of seconds).
+        :param interval: The number of seconds to delay garbage collection when
+                         `force` is :data:`False` (a number, defaults to the
+                         equivalent of 24 hours).
         """
         timer = Timer()
         num_checked = 0
@@ -167,7 +168,11 @@ def collect_garbage(self, force=False, interval=60 * 60 * 24):
         elif force:
             logger.info("Performing forced garbage collection ..")
         else:
-            # Check when garbage collection was last run.
+            # Check whether garbage collection is needed, the idea being that
+            # garbage collection can be expensive (given enough cache entries
+            # and/or a cold enough disk cache) so we'd rather not do it when
+            # it's not necessary.
+            logger.debug("Checking whether garbage collection is necessary ..")
             try:
                 last_gc = os.path.getmtime(marker_file)
             except Exception:
@@ -203,10 +208,14 @@ def collect_garbage(self, force=False, interval=60 * 60 * 24):
         # Record when garbage collection was last run.
         with open(marker_file, 'a') as handle:
             os.utime(marker_file, None)
-        logger.debug("Checked %s, garbage collected %s in %s.",
-                     pluralize(num_checked, "cache entry", "cache entries"),
-                     pluralize(num_deleted, "cache entry", "cache entries"),
-                     timer)
+        status_level = logging.INFO if force else logging.DEBUG
+        if num_checked == 0:
+            logger.log(status_level, "Nothing to garbage collect (the cache is empty).")
+        else:
+            logger.log(status_level, "Checked %s, garbage collected %s in %s.",
+                       pluralize(num_checked, "cache entry", "cache entries"),
+                       pluralize(num_deleted, "cache entry", "cache entries"),
+                       timer)
 
 
 class CacheEntry(object):

deb_pkg_tools/cli.py

@@ -1,7 +1,7 @@
 # Debian packaging tools: Command line interface
 #
 # Author: Peter Odding <peter@peterodding.com>
-# Last Change: November 23, 2016
+# Last Change: November 24, 2016
 # URL: https://github.com/xolox/python-deb-pkg-tools
 
 """
@@ -15,11 +15,12 @@
 
   -i, --inspect=FILE
 
-    Inspect the metadata in the Debian binary package archive given by FILE.
+    Inspect the metadata in the Debian binary package archive given by FILE
+    (similar to `dpkg --info').
 
   -c, --collect=DIR
 
-    Copy the package archive(s) given as positional arguments (and all packages
+    Copy the package archive(s) given as positional arguments (and all package
     archives required by the given package archives) into the directory given
     by DIR.
 
@@ -68,6 +69,15 @@
     the positional arguments as an external command (usually `apt-get install')
     and finally deactivate the repository.
 
+  --gc, --garbage-collect
+
+    Force removal of stale entries from the persistent (on disk) package
+    metadata cache. Garbage collection is performed automatically by the
+    deb-pkg-tools command line interface when the last garbage collection
+    cycle was more than 24 hours ago, so you only need to do it manually
+    when you want to control when it happens (for example by a daily
+    cron job scheduled during idle hours :-).
+
   -y, --yes
 
     Assume the answer to interactive questions is yes.
@@ -95,7 +105,7 @@
 # External dependencies.
 import coloredlogs
 from humanfriendly import format_path, format_size, parse_path
-from humanfriendly.text import format, pluralize
+from humanfriendly.text import compact, format, pluralize
 from humanfriendly.prompts import prompt_for_confirmation
 from humanfriendly.terminal import (
     HIGHLIGHT_COLOR,
@@ -138,7 +148,7 @@ def main():
         options, arguments = getopt.getopt(sys.argv[1:], 'i:c:C:p:s:b:u:a:d:w:yvh', [
             'inspect=', 'collect=', 'check=', 'patch=', 'set=', 'build=',
             'update-repo=', 'activate-repo=', 'deactivate-repo=', 'with-repo=',
-            'yes', 'verbose', 'help'
+            'gc', 'garbage-collect', 'yes', 'verbose', 'help'
         ])
         for option, value in options:
             if option in ('-i', '--inspect'):
@@ -177,6 +187,8 @@ def main():
                                                  directory=check_directory(value),
                                                  command=arguments,
                                                  cache=cache))
+            elif option in ('--gc', '--garbage-collect'):
+                actions.append(functools.partial(cache.collect_garbage, force=True))
             elif option in ('-y', '--yes'):
                 prompt = False
             elif option in ('-v', '--verbose'):