Optimistically check if we need to do anything on a pull (#531)

* Optimistically check if we need to do anything on a pull Right now on a pull we always acquire a lock for a registry host. This is problematic because, for example, host can be pulling `ghcr.io/cirruslabs/macos-ventura-xcode:15-beta-2` image when a new request will come to pull `ghcr.io/cirruslabs/macos-ventura-xcode:latest` if needed. In this situation, even though `ghcr.io/cirruslabs/macos-ventura-xcode:latest` is already cached and linked, `tart pull` will wait for a lock. This change optimistically check if there is something to do at all before acquiring a lock. * Fix linter errors --------- Co-authored-by: Nikolay Edigaryev <[email protected]>
cirruslabs · Jun 29, 2023 · 415ed33 · 415ed33
1 parent 870b414
commit 415ed33
Showing 1 changed file with 15 additions and 0 deletions.
diff --git a/Sources/tart/VMStorageOCI.swift b/Sources/tart/VMStorageOCI.swift
@@ -144,6 +144,12 @@ class VMStorageOCI: PrunableStorage {
     let digestName = RemoteName(host: name.host, namespace: name.namespace,
                                 reference: Reference(digest: Digest.hash(manifestData)))
 
+    if exists(name) && exists(digestName) && linked(from: name, to: digestName) {
+      // optimistically check if we need to do anything at all before locking
+      defaultLogger.appendNewLine("\(digestName) image is already cached and linked!")
+      return
+    }
+
     // Ensure that host directory for given RemoteName exists in OCI storage
     let hostDirectoryURL = hostDirectoryURL(digestName)
     try FileManager.default.createDirectory(at: hostDirectoryURL, withIntermediateDirectories: true)
@@ -203,6 +209,15 @@ class VMStorageOCI: PrunableStorage {
     }
   }
 
+  func linked(from: RemoteName, to: RemoteName) -> Bool {
+    do {
+      let resolvedFrom = try FileManager.default.destinationOfSymbolicLink(atPath: vmURL(from).path)
+      return resolvedFrom == vmURL(to).path
+    } catch {
+      return false
+    }
+  }
+
   func link(from: RemoteName, to: RemoteName) throws {
     if FileManager.default.fileExists(atPath: vmURL(from).path) {
       try FileManager.default.removeItem(at: vmURL(from))