Utilities and cleanups for socket. (#9576)

- Use c++-17 nodiscard and nested ns.
- Add bind method to socket.
- Remove rabit parameters.

src/collective/communicator.cc

@@ -11,9 +11,7 @@
 #include "../../plugin/federated/federated_communicator.h"
 #endif
 
-namespace xgboost {
-namespace collective {
-
+namespace xgboost::collective {
 thread_local std::unique_ptr<Communicator> Communicator::communicator_{new NoOpCommunicator()};
 thread_local CommunicatorType Communicator::type_{};
 
@@ -57,6 +55,4 @@ void Communicator::Finalize() {
   communicator_.reset(new NoOpCommunicator());
 }
 #endif
-
-}  // namespace collective
-}  // namespace xgboost
+}  // namespace xgboost::collective

src/collective/socket.cc

@@ -3,6 +3,7 @@
  */
 #include "xgboost/collective/socket.h"
 
+#include <array>         // for array
 #include <cstddef>       // std::size_t
 #include <cstdint>       // std::int32_t
 #include <cstring>       // std::memcpy, std::memset
@@ -92,13 +93,18 @@ std::size_t TCPSocket::Recv(std::string *p_str) {
 
   conn = TCPSocket::Create(addr.Domain());
   CHECK_EQ(static_cast<std::int32_t>(conn.Domain()), static_cast<std::int32_t>(addr.Domain()));
-  conn.SetNonBlock(true);
+  auto non_blocking = conn.NonBlocking();
+  auto rc = conn.NonBlocking(true);
+  if (!rc.OK()) {
+    return Fail("Failed to set socket option.", std::move(rc));
+  }
 
   Result last_error;
-  auto log_failure = [&host, &last_error](Result err, char const *file, std::int32_t line) {
+  auto log_failure = [&host, &last_error, port](Result err, char const *file, std::int32_t line) {
     last_error = std::move(err);
     LOG(WARNING) << std::filesystem::path{file}.filename().string() << "(" << line
-                 << "): Failed to connect to:" << host << " Error:" << last_error.Report();
+                 << "): Failed to connect to:" << host << ":" << port
+                 << " Error:" << last_error.Report();
   };
 
   for (std::int32_t attempt = 0; attempt < std::max(retry, 1); ++attempt) {
@@ -138,12 +144,9 @@ std::size_t TCPSocket::Recv(std::string *p_str) {
         continue;
       }
 
-      conn.SetNonBlock(false);
-      return Success();
-
+      return conn.NonBlocking(non_blocking);
     } else {
-      conn.SetNonBlock(false);
-      return Success();
+      return conn.NonBlocking(non_blocking);
     }
   }
 
@@ -152,4 +155,13 @@ std::size_t TCPSocket::Recv(std::string *p_str) {
   conn.Close();
   return Fail(ss.str(), std::move(last_error));
 }
+
+[[nodiscard]] Result GetHostName(std::string *p_out) {
+  std::array<char, HOST_NAME_MAX> buf;
+  if (gethostname(&buf[0], HOST_NAME_MAX) != 0) {
+    return system::FailWithCode("Failed to get host name.");
+  }
+  *p_out = buf.data();
+  return Success();
+}
 }  // namespace xgboost::collective