Addressing github comments.

include/grpc++/credentials.h

@@ -97,20 +97,20 @@ std::unique_ptr<Credentials> ComputeEngineCredentials();
 // Builds service account credentials.
 // json_key is the JSON key string containing the client's private key.
 // scope is a space-delimited list of the requested permissions.
-// token_lifetime is the lifetime of each token acquired through this service
+// token_lifetime_seconds is the lifetime in seconds of each token acquired
-// account credentials. It should be positive and should not exceed
+// through this service account credentials. It should be positive and should
-// grpc_max_auth_token_lifetime or will be cropped to this value.
+// not exceed grpc_max_auth_token_lifetime or will be cropped to this value.
 std::unique_ptr<Credentials> ServiceAccountCredentials(
     const grpc::string& json_key, const grpc::string& scope,
-    long token_lifetime);
+    long token_lifetime_seconds);
 
 // Builds JWT credentials.
 // json_key is the JSON key string containing the client's private key.
-// token_lifetime is the lifetime of each Json Web Token (JWT) created with
+// token_lifetime_seconds is the lifetime in seconds of each Json Web Token
-// this credentials.  It should not exceed grpc_max_auth_token_lifetime or
+// (JWT) created with this credentials. It should not exceed
-// will be cropped to this value.
+// grpc_max_auth_token_lifetime or will be cropped to this value.
 std::unique_ptr<Credentials> JWTCredentials(
-    const grpc::string& json_key, long token_lifetime);
+    const grpc::string& json_key, long token_lifetime_seconds);
 
 // Builds refresh token credentials.
 // json_refresh_token is the JSON string containing the refresh token along

include/grpc++/time.h

@@ -38,11 +38,33 @@
 
 namespace grpc {
 
+/* If you are trying to use CompletionQueue::AsyncNext with a time class that
+   isn't either gpr_timespec or std::chrono::system_clock::time_point, you
+   will most likely be looking at that comment as your compiler will have
+   fired the static_assert below. In order to fix that issue, you have two
+   potential solutions:
+
+     1. Use gpr_timespec or std::chrono::system_clock::time_point instead
+     2. Specialize the TimePoint class with whichever time class that you
+        want to use here. See below for two examples of how to do that.
+ */
+
 template <typename T>
 class TimePoint {
  public:
-  TimePoint(const T& time) : time_(time) { }
+  TimePoint(const T& time) {
-  gpr_timespec raw_time() const { return time_; }
+    static_assert(false, "You need a specialization of TimePoint");
+  }
+  gpr_timespec raw_time() {
+    static_assert(false, "You need a specialization of TimePoint");
+  }
+};
+
+template<>
+class TimePoint<gpr_timespec> {
+ public:
+  TimePoint(const gpr_timespec& time) : time_(time) { }
+  gpr_timespec raw_time() { return time_; }
  private:
   gpr_timespec time_;
 };