treemanifest: don't purge shared packs while repack is running

Summary:
If treemanifest finds there are too many shared packs (more than
`packs.maxpackfilecount`) then it will purge them.  This is a shame if there is
currently a repack in progress, as it will purge the packfiles from underneath
the repack, deleting lots of cache data that will be imminently repacked).

Skip the purge if there is a repack ongoing.

Reviewed By: mitrandir77

Differential Revision: D17155854

fbshipit-source-id: 20d46f29c252e508177b1fde08ca7a69841dcd7e

edenscm/hgext/treemanifest/__init__.py

@@ -191,6 +191,7 @@ from edenscm.mercurial.node import bin, hex, nullid, short
 from edenscmnative import cstore
 from edenscmnative.bindings import manifest as rustmanifest, revisionstore
 
+from ..extutil import flock
 from ..remotefilelog import (
     cmdtable as remotefilelogcmdtable,
     edenapi,
@@ -211,6 +212,7 @@ from ..remotefilelog.repack import (
     _runrepack,
     _topacks,
     domaintenancerepack,
+    repacklockvfs,
 )
 
 
@@ -628,13 +630,27 @@ def _prunesharedpacks(repo, packpath):
         # Note this is based on file count, not pack count.
         config = repo.ui.configint("packs", "maxpackfilecount")
         if config and numentries > config:
-            repo.ui.warn(
-                (
-                    "purging shared treemanifest pack cache (%d entries) "
-                    "-- too many files\n" % numentries
+            try:
+                with flock(
+                    repacklockvfs(repo).join("repacklock"),
+                    _("purging excess packs for %s") % packpath,
+                    timeout=0,
+                ):
+                    repo.ui.warn(
+                        (
+                            "purging shared treemanifest pack cache (%d entries) "
+                            "-- too many files\n" % numentries
+                        )
+                    )
+                    shutil.rmtree(packpath, True)
+            except error.LockHeld:
+                repo.ui.warn(
+                    (
+                        "not purging shared treemanifest pack cache (%d entries) "
+                        "as repack is still running\n"
+                    )
+                    % numentries
                 )
-            )
-            shutil.rmtree(packpath, True)
     except OSError:
         pass
 

tests/test-fb-hgext-treemanifest-repack.t

@@ -1,3 +1,4 @@
+  $ enable amend
   $ setconfig extensions.treemanifest=!
   $ . "$TESTDIR/library.sh"
   $ setconfig treemanifest.treeonly=False
@@ -272,11 +273,14 @@ Test incremental repack that doesn't take all packs
   $ ls_l .hg/cache/packs/manifests/ | grep datapack
   -r--r--r--     496 bc6c2ebb080844d7a227dacbc847a5b375ec620c.datapack
 
-- Test pruning the manifest cache using packs.maxpackfilecount
-  $ hg repack --incremental --config packs.maxpackfilecount=0
-  $ hg repack --incremental --packsonly --config packs.maxpackfilecount=1
+- Test pruning the manifest cache using packs.maxpackfilecount.
+- (Use 'hg metaedit' as repack itself will not trigger the purge, and
+- 'metaedit' won't create any new objects to pack.)
+  $ hg metaedit -m 'modify a (2)' --config packs.maxpackfilecount=0
+  $ hg metaedit -m 'modify a (3)' --config packs.maxpackfilecount=1
   purging shared treemanifest pack cache (4 entries) -- too many files
-  $ ls_l .hg/cache/packs/manifests/
+  $ test -d .hg/cache/packs/manifests/
+  [1]
   $ cd ..
 
 Test hg gc with multiple repositories