[llvm] [CAS] Add UnifiedOnDiskCache and OnDiskCAS (PR #114103)

[Steven Wu via llvm-commits]

================
@@ -47,12 +51,54 @@ class InMemoryActionCache final : public ActionCache {
   Expected<std::optional<CASID>> getImpl(ArrayRef<uint8_t> ActionKey,
                                          bool CanBeDistributed) const final;
 
+  Error validate() const final {
+    return createStringError("InMemoryActionCache doesn't support validate()");
+  }
+
 private:
   using DataT = CacheEntry<sizeof(HashType)>;
   using InMemoryCacheT = ThreadSafeTrieRawHashMap<DataT, sizeof(HashType)>;
 
   InMemoryCacheT Cache;
 };
+
+/// Builtin basic OnDiskActionCache that uses one underlying OnDiskKeyValueDB.
+class OnDiskActionCache final : public ActionCache {
+public:
+  Error putImpl(ArrayRef<uint8_t> ActionKey, const CASID &Result,
+                bool CanBeDistributed) final;
+  Expected<std::optional<CASID>> getImpl(ArrayRef<uint8_t> ActionKey,
+                                         bool CanBeDistributed) const final;
+
+  static Expected<std::unique_ptr<OnDiskActionCache>> create(StringRef Path);
+
+  Error validate() const final;
+
+private:
+  static StringRef getHashName() { return "BLAKE3"; }
+
+  OnDiskActionCache(std::unique_ptr<ondisk::OnDiskKeyValueDB> DB);
+
+  std::unique_ptr<ondisk::OnDiskKeyValueDB> DB;
+  using DataT = CacheEntry<sizeof(HashType)>;
+};
+
+/// Builtin unified ActionCache that wraps around UnifiedOnDiskCache to privode
+/// access to its ActionCache.
+class UnifiedOnDiskActionCache final : public ActionCache {
+public:
+  Error putImpl(ArrayRef<uint8_t> ActionKey, const CASID &Result,
+                bool CanBeDistributed) final;
+  Expected<std::optional<CASID>> getImpl(ArrayRef<uint8_t> ActionKey,
+                                         bool CanBeDistributed) const final;
+
+  UnifiedOnDiskActionCache(std::shared_ptr<ondisk::UnifiedOnDiskCache> UniDB);
+
+  Error validate() const final;
+
+private:
+  std::shared_ptr<ondisk::UnifiedOnDiskCache> UniDB;
----------------
cachemeifyoucan wrote:

This is just extending the lifetime of the wrapped `UnifiedOnDiskCache` to make sure it is not deleted when ActionCache is still in use.

Alternatively, we can leave this as a raw pointer and left the life-time management to user, but since this is not really a ref-count that is being updated often, this safe guard is pretty safe to keep.

https://github.com/llvm/llvm-project/pull/114103