_artifactcache: There shalt be only one cache size

This does a lot of house cleaning, finally bringing cache
cleanup logic to a level of comprehensibility.

Changes in this commit include:

  o _artifactcache/artifactcache.py: _cache_size, _cache_quota and
    _cache_lower_threshold are now all private variables.

    get_approximate_cache_size() is now get_cache_size()

    Added get_quota_exceeded() for the purpose of safely checking
    if we have exceeded the quota.

    set_cache_size() now asserts that the passed size is not None,
    it is not acceptable to set a None size cache anymore.

  o _artifactcache/cascache.py: No longer set the ArtifactCache
    'cache_size' variable violently in the commit() method.

    Also the calculate_cache_size() method now unconditionally
    calculates the cache size, that is what it's for.

  o _scheduler/jobs/cachesizejob.py & _scheduler/jobs/cleanupjob.py:

    Now check the success status. Don't try to set the cache size
    in the case that the job was terminated.

  o _scheduler/jobs/elementjob.py & _scheduler/queues/queue.py:

    No longer passing around the cache size from child tasks,
    this happens only explicitly, not implicitly for all tasks.

  o _scheduler/queues/buildqueue.py & _scheduler/scheduler.py:

    Use get_quota_exceeded() accessor

This is a part of #623

1 files changed, 5 insertions, 3 deletions

diff --git a/buildstream/_scheduler/jobs/cachesizejob.py b/buildstream/_scheduler/jobs/cachesizejob.py
index 9c1a4bc97..68cd91331 100644
--- a/buildstream/_scheduler/jobs/cachesizejob.py
+++ b/buildstream/_scheduler/jobs/cachesizejob.py
@@ -32,9 +32,11 @@ class CacheSizeJob(Job):
         return self._artifacts.compute_cache_size()
 
     def parent_complete(self, success, result):
-        self._artifacts.set_cache_size(result)
-        if self._complete_cb:
-            self._complete_cb(result)
+        if success:
+            self._artifacts.set_cache_size(result)
+
+            if self._complete_cb:
+                self._complete_cb(result)
 
     def child_process_data(self):
         return {}