add code comments && move brpc::policy::HashFunc to hasher.cpp

src/brpc/load_balancer.h

@@ -104,7 +104,8 @@ public:
     // Caller is responsible for Destroy() the instance after usage.
     virtual LoadBalancer* New() const = 0;
 
-    // Set other
+    // Config user passed parameters to lb after constrction which 
+    // make lb function more flexible.
     virtual bool SetParameters(const butil::StringPairs& params) { return true; }
 
 protected:

src/brpc/policy/consistent_hashing_load_balancer.cpp

@@ -35,7 +35,7 @@ namespace {
 
 bool BuildReplicasDefault(const ServerId server,
                           const size_t num_replicas,
-                          ConsistentHashingLoadBalancer::HashFunc hash,
+                          HashFunc hash,
                           std::vector<ConsistentHashingLoadBalancer::Node>* replicas) {
     SocketUniquePtr ptr;
     if (Socket::AddressFailedAsWell(server.id, &ptr) == -1) {

src/brpc/policy/consistent_hashing_load_balancer.h

@@ -43,7 +43,6 @@ public:
             return hash < code;
         }
     };
-    using HashFunc = uint32_t(*)(const void*, size_t);
     using BuildReplicasFunc = 
         std::function<bool (const ServerId server, const size_t num_replicas, std::vector<Node>* replicas)>;
     explicit ConsistentHashingLoadBalancer(const char* name);

src/brpc/policy/hasher.cpp

@@ -155,7 +155,7 @@ uint32_t CRCHash32(const void* key, size_t len) {
     return ((~crc) >> 16) & 0x7fff;
 }
 
-const char *GetHashName(uint32_t (*hasher)(const void* key, size_t len)) {
+const char *GetHashName(HashFunc hasher) {
     if (hasher == MurmurHash32) {
         return "murmurhash3";
     }

src/brpc/policy/hasher.h

@@ -25,6 +25,8 @@
 namespace brpc {
 namespace policy {
 
+using HashFunc = uint32_t(*)(const void*, size_t);
+
 void MD5HashSignature(const void* key, size_t len, unsigned char* results);
 uint32_t MD5Hash32(const void* key, size_t len);
 uint32_t MD5Hash32V(const butil::StringPiece* keys, size_t num_keys);

test/brpc_load_balancer_unittest.cpp

@@ -485,7 +485,7 @@ TEST_F(LoadBalancerTest, fairness) {
 }
 
 TEST_F(LoadBalancerTest, consistent_hashing) {
-    ::brpc::policy::ConsistentHashingLoadBalancer::HashFunc hashs[] = {
+    ::brpc::policy::HashFunc hashs[] = {
             ::brpc::policy::MurmurHash32, 
             ::brpc::policy::MD5Hash32,
             ::brpc::policy::KetamaHash