Switch from custom hash_mix to absl::Hash. (#370)

The hash_mix code pre-dates absl::Hash.

Author: g-easy

opencensus/common/internal/BUILD

@@ -20,12 +20,6 @@ licenses(["notice"])  # Apache 2.0
 
 package(default_visibility = ["//opencensus:__subpackages__"])
 
-cc_library(
-    name = "hash_mix",
-    hdrs = ["hash_mix.h"],
-    copts = DEFAULT_COPTS,
-)
-
 cc_library(
     name = "hostname",
     srcs = ["hostname.cc"],
@@ -62,7 +56,7 @@ cc_library(
     name = "string_vector_hash",
     hdrs = ["string_vector_hash.h"],
     copts = DEFAULT_COPTS,
-    deps = [":hash_mix"],
+    deps = ["@com_google_absl//absl/hash"],
 )
 
 # Tests

opencensus/common/internal/CMakeLists.txt

@@ -12,8 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-opencensus_lib(common_hash_mix)
-
 opencensus_lib(common_hostname
                SRCS
                hostname.cc
@@ -34,7 +32,7 @@ opencensus_lib(common_stats_object DEPS absl::time)
 target_compile_definitions(opencensus_common_stats_object INTERFACE
                            $<$<CXX_COMPILER_ID:MSVC>:NOMINMAX>)
 
-opencensus_lib(common_string_vector_hash)
+opencensus_lib(common_string_vector_hash DEPS absl::hash)
 
 opencensus_test(common_hostname_test hostname_test.cc common_hostname)
 

opencensus/common/internal/hash_mix.h

@@ -19,19 +19,14 @@
 #include <string>
 #include <vector>
 
-#include "opencensus/common/internal/hash_mix.h"
+#include "absl/hash/hash.h"
 
 namespace opencensus {
 namespace common {
 
 struct StringVectorHash {
   std::size_t operator()(const std::vector<std::string>& container) const {
-    std::hash<std::string> hasher;
-    HashMix mixer;
-    for (const auto& elem : container) {
-      mixer.Mix(hasher(elem));
-    }
-    return mixer.get();
+    return absl::Hash<std::vector<std::string>>()(container);
   }
 };
 

opencensus/common/internal/string_vector_hash.h

@@ -34,8 +34,8 @@ cc_library(
     copts = DEFAULT_COPTS,
     visibility = ["//visibility:public"],
     deps = [
-        "//opencensus/common/internal:hash_mix",
         "@com_google_absl//absl/base:core_headers",
+        "@com_google_absl//absl/hash",
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/synchronization",
     ],

opencensus/tags/BUILD

@@ -19,8 +19,8 @@ opencensus_lib(tags
                internal/tag_map.cc
                DEPS
                absl::strings
-               common_hash_mix
                absl::base
+               absl::hash
                absl::synchronization)
 
 opencensus_lib(tags_context_util

opencensus/tags/CMakeLists.txt

@@ -14,6 +14,7 @@
 
 #include "opencensus/tags/tag_key.h"
 
+#include "absl/hash/hash.h"
 #include "gtest/gtest.h"
 
 namespace opencensus {
@@ -29,14 +30,14 @@ TEST(TagKeyTest, DuplicateRegistrationsEqual) {
   TagKey k1 = TagKey::Register("key");
   TagKey k2 = TagKey::Register("key");
   EXPECT_EQ(k1, k2);
-  EXPECT_EQ(k1.hash(), k2.hash());
+  EXPECT_EQ(absl::Hash<TagKey>()(k1), absl::Hash<TagKey>()(k2));
 }
 
 TEST(TagKeyTest, Inequality) {
   TagKey k1 = TagKey::Register("k1");
   TagKey k2 = TagKey::Register("k2");
   EXPECT_NE(k1, k2);
-  EXPECT_NE(k1.hash(), k2.hash());
+  EXPECT_NE(absl::Hash<TagKey>()(k1), absl::Hash<TagKey>()(k2));
 }
 
 }  // namespace

opencensus/tags/internal/tag_key_test.cc

@@ -21,10 +21,10 @@
 #include <utility>
 #include <vector>
 
+#include "absl/hash/hash.h"
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_join.h"
 #include "absl/strings/string_view.h"
-#include "opencensus/common/internal/hash_mix.h"
 #include "opencensus/tags/tag_key.h"
 
 namespace opencensus {
@@ -57,13 +57,7 @@ void TagMap::Initialize() {
          "Duplicate keys are not allowed in TagMap.");
 #endif
 
-  std::hash<std::string> hasher;
-  common::HashMix mixer;
-  for (const auto& tag : tags_) {
-    mixer.Mix(tag.first.hash());
-    mixer.Mix(hasher(tag.second));
-  }
-  hash_ = mixer.get();
+  hash_ = absl::Hash<std::vector<std::pair<TagKey, std::string>>>()(tags_);
 }
 
 std::size_t TagMap::Hash::operator()(const TagMap& tags) const {

opencensus/tags/internal/tag_map.cc

@@ -19,6 +19,8 @@
 #include <cstdint>
 #include <string>
 
+#include "absl/base/macros.h"
+#include "absl/hash/hash.h"
 #include "absl/strings/string_view.h"
 
 namespace opencensus {
@@ -40,8 +42,16 @@ class TagKey final {
   bool operator<(TagKey other) const { return id_ < other.id_; }
 
   // Returns a suitable hash of the TagKey. The implementation may change.
+  ABSL_DEPRECATED(
+      "Use absl::Hash<TagKey>()(...) instead. "
+      "This method will be removed on or after 2020-02-06")
   std::size_t hash() const { return id_; }
 
+  template <typename H>
+  friend H AbslHashValue(H state, const TagKey& k) {
+    return H::combine(std::move(state), k.id_);
+  }
+
  private:
   friend class TagKeyRegistry;
   explicit TagKey(uint64_t id) : id_(id) {}