Introduce a 'weak' and mutable version of slice hash table

1 files changed, 105 insertions, 0 deletions

diff --git a/src/core/lib/slice/slice_weak_hash_table.h b/src/core/lib/slice/slice_weak_hash_table.h
new file mode 100644
index 0000000000..9d0ddfc2d2
--- /dev/null
+++ b/src/core/lib/slice/slice_weak_hash_table.h
@@ -0,0 +1,105 @@
+/*
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef GRPC_CORE_LIB_SLICE_SLICE_WEAK_HASH_TABLE_H
+#define GRPC_CORE_LIB_SLICE_SLICE_WEAK_HASH_TABLE_H
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/lib/gprpp/memory.h"
+#include "src/core/lib/gprpp/ref_counted.h"
+#include "src/core/lib/gprpp/ref_counted_ptr.h"
+#include "src/core/lib/slice/slice_internal.h"
+
+/// Weak hash table implementation.
+///
+/// This entries in this table are weak: an entry may be removed at any time due
+/// to a number of reasons: memory pressure, hash collisions, etc.
+///
+/// The keys are \a grpc_slice objects. The values are of arbitrary type.
+///
+/// This class is thread unsafe. It's the caller's responsibility to ensure
+/// proper locking when accessing its methods.
+
+namespace grpc_core {
+
+template <typename T, size_t Size>
+class SliceWeakHashTable : public RefCounted<SliceWeakHashTable<T, Size>> {
+ public:
+  /// Creates a new table of at most \a size entries.
+  static RefCountedPtr<SliceWeakHashTable> Create() {
+    return MakeRefCounted<SliceWeakHashTable<T, Size>>();
+  }
+
+  /// Add a mapping from \a key to \a value, taking ownership of \a key. This
+  /// operation will always succeed. It may discard older entries.
+  void Add(grpc_slice key, T value) {
+    const size_t idx = grpc_slice_hash(key) % Size;
+    entries_[idx].Set(key, std::move(value));
+    return;
+  }
+
+  /// Returns the value from the table associated with / \a key or null if not
+  /// found.
+  const T* Get(const grpc_slice key) const {
+    const size_t idx = grpc_slice_hash(key) % Size;
+    const auto& entry = entries_[idx];
+    return grpc_slice_eq(entry.key(), key) ? entry.value() : nullptr;
+  }
+
+ private:
+  // So New() can call our private ctor.
+  template <typename T2, typename... Args>
+  friend T2* New(Args&&... args);
+
+  SliceWeakHashTable() = default;
+  ~SliceWeakHashTable() = default;
+
+  /// The type of the table "rows".
+  class Entry {
+   public:
+    Entry() = default;
+    ~Entry() {
+      if (is_set_) grpc_slice_unref_internal(key_);
+    }
+    grpc_slice key() const { return key_; }
+
+    /// Return the entry's value, or null if unset.
+    const T* value() const {
+      if (!is_set_) return nullptr;
+      return &value_;
+    }
+
+    /// Set the \a key and \a value (which is moved) for the entry.
+    void Set(grpc_slice key, T&& value) {
+      if (is_set_) grpc_slice_unref_internal(key_);
+      key_ = key;
+      value_ = std::move(value);
+      is_set_ = true;
+    }
+
+   private:
+    grpc_slice key_;
+    T value_;
+    bool is_set_ = false;
+  };
+
+  Entry entries_[Size];
+};
+
+}  // namespace grpc_core
+
+#endif /* GRPC_CORE_LIB_SLICE_SLICE_WEAK_HASH_TABLE_H */