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Open a directory store without creating anything

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Opening a directory store, read-only or writable, created the .records
folder and its .commit.lock before reading a manifest that might not
exist. Only a write creates them now: PullAll takes the commit lease with
create: false, which opens an existing lock and returns no lease when
there is none (no writer has ever committed there, so there is nothing to
exclude). CommitBatch and PushAll create the folder and lock as before.

Test DirectoryMessagePackBackingStore_Open_CreatesNothing_UntilAWrite:
opening a missing store and a manifest-less .records folder, read-only
and writable, leaves the filesystem unchanged; the first flush creates the
manifest, the lock and one page. With the previous lease code restored
the test fails on the first read-only open.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Meta Vens 2026-09-14 13:43:45 +02:00
commit debe616716
7 changed files with 66 additions and 120 deletions
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23
src/GameCult.Caching.MessagePack/DirectoryMessagePackBackingStore.cs
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@ -57,7 +57,7 @@ public sealed class DirectoryMessagePackBackingStore : CacheBackingStore
var reports = new List<CultSchemaMigrationReport>();
var loaded = new Dictionary<string, CultStoredDocument>(StringComparer.Ordinal);
CultSchemaCatalogEntry[] catalog;
using (AcquireCommitLease(wait: true))
using (AcquireCommitLease(wait: true, create: false))
{
// Only pages named by the manifest read under the lease are loaded; orphaned pages are never loaded.
var manifest = ReadManifest();
@ -131,7 +131,7 @@ public sealed class DirectoryMessagePackBackingStore : CacheBackingStore
return Held(() =>
{
Directory.CreateDirectory(_manifestFile.DirectoryName!);
using var commitLease = AcquireCommitLease(wait);
using var commitLease = AcquireCommitLease(wait, create: true);
if (commitLease == null)
return CultCommitOutcome.Contended;
var manifest = ReadManifest();
@ -186,7 +186,7 @@ public sealed class DirectoryMessagePackBackingStore : CacheBackingStore
return;
Directory.CreateDirectory(_manifestFile.DirectoryName!);
using var commitLease = AcquireCommitLease(wait: true);
using var commitLease = AcquireCommitLease(wait: true, create: true);
WriteGeneration(ReadManifest());
});
}
@ -470,9 +470,12 @@ public sealed class DirectoryMessagePackBackingStore : CacheBackingStore
return buffer.ToArray();
}
private FileStream? AcquireCommitLease(bool wait)
// Only a writer creates the records folder and the lock. A reader opens an existing lock; with none, no writer has ever
// committed here, so there is nothing to exclude and opening the store creates nothing.
private FileStream? AcquireCommitLease(bool wait, bool create)
{
Directory.CreateDirectory(_recordDirectory.FullName);
if (create)
Directory.CreateDirectory(_recordDirectory.FullName);
var lockPath = Path.Combine(_recordDirectory.FullName, ".commit.lock");
var started = Stopwatch.StartNew();
while (true)
@ -481,12 +484,20 @@ public sealed class DirectoryMessagePackBackingStore : CacheBackingStore
{
return new FileStream(
lockPath,
FileMode.OpenOrCreate,
create ? FileMode.OpenOrCreate : FileMode.Open,
FileAccess.ReadWrite,
FileShare.None,
bufferSize: 1,
FileOptions.WriteThrough);
}
catch (FileNotFoundException) when (!create)
{
return null;
}
catch (DirectoryNotFoundException) when (!create)
{
return null;
}
catch (IOException) when (!wait)
{
return null;