fix(mgb/zmq): fix unused-result when compiling with c++17

GitOrigin-RevId: cbdffd39c65057b3389d96b469db95fff77d291e

src/opr-mm/impl/zmq_rpc.cpp

-#include "megbrain/opr/zmq_rpc.h"
-#include "megbrain/exception.h"
 #include "megbrain_build_config.h"
 
 #if MGB_CUDA
+#include "megbrain/opr/zmq_rpc.h"
+#include "megbrain/common.h"
+#include "megbrain/exception.h"
+
 #include <unistd.h>
 #include <cassert>
 #include <cstdio>
@@ -18,6 +20,8 @@ using namespace std;
 using namespace zmq;
 using namespace ZmqRpc;
 
+#define DISCARD_RETVAL MGB_MARK_USED_VAR
+
 ZmqRpcWorker::ZmqRpcWorker(context_t* context, ZmqRpcServerImpl* impl)
         : m_ctx(context), m_runable(0), m_impl(impl) {}
 
@@ -57,10 +61,10 @@ void ZmqRpcWorker::work(string uid) {
         if (m_stop)
             break;
         message_t empty;
-        socket.recv(empty);
+        DISCARD_RETVAL(socket.recv(empty));
         assert(empty.size() == 0);
         message_t request;
-        socket.recv(request);
+        DISCARD_RETVAL(socket.recv(request));
 
         m_mtx.lock();
         if (--m_runable <= 0) {
@@ -144,24 +148,24 @@ void ZmqRpcServer::work() {
         if (items[0].revents & ZMQ_POLLIN) {
             message_t address;
 
-            m_backend.recv(address);
+            DISCARD_RETVAL(m_backend.recv(address));
             worker_queue.push({(char*)address.data(), address.size()});
 
             message_t empty;
-            m_backend.recv(empty);
+            DISCARD_RETVAL(m_backend.recv(empty));
             assert(empty.size() == 0);
 
 	    // the third frame is READY or a client address
             message_t client_address;
-            m_backend.recv(client_address);
+            DISCARD_RETVAL(m_backend.recv(client_address));
             string tmp((char*)client_address.data(), client_address.size());
             if (strcmp(tmp.c_str(), "READY") != 0) {
                 empty.rebuild();
-                m_backend.recv(empty);
+                DISCARD_RETVAL(m_backend.recv(empty));
                 assert(empty.size() == 0);
 
                 message_t respones;
-                m_backend.recv(respones);
+                DISCARD_RETVAL(m_backend.recv(respones));
                 m_frontend.send(client_address, send_flags::sndmore);
                 m_frontend.send(empty, send_flags::sndmore);
                 m_frontend.send(respones, send_flags::dontwait);
@@ -169,14 +173,14 @@ void ZmqRpcServer::work() {
         }
         if (items[1].revents & ZMQ_POLLIN) {
             message_t address;
-            m_frontend.recv(address);
+            DISCARD_RETVAL(m_frontend.recv(address));
 
             message_t empty;
-            m_frontend.recv(empty);
+            DISCARD_RETVAL(m_frontend.recv(empty));
             assert(empty.size() == 0);
 
             message_t request;
-            m_frontend.recv(request);
+            DISCARD_RETVAL(m_frontend.recv(request));
 
             string worker_uid = worker_queue.front();
             worker_queue.pop();
@@ -221,7 +225,7 @@ void ZmqRpcClient::add_socket(socket_t* socket) {
 void ZmqRpcClient::request(message_t& request, message_t& reply) {
     socket_t* client = get_socket();
     client->send(request, send_flags::dontwait);
-    client->recv(reply);
+    DISCARD_RETVAL(client->recv(reply));
     add_socket(client);
 }
-#endif
+#endif // MGB_CUDA