[EchoServer] add configurable computation part in us spent busy looping

apps/EchoServer.cpp

@@ -4,6 +4,7 @@
 #include <sys/types.h>
 
 #include <cerrno>
+#include <chrono>
 #include <cstdlib>
 #include <cstring>
 #include <iostream>
@@ -12,17 +13,24 @@
 #include "Common.hpp"
 #include "Debug.hpp"
 #include "Runtime.hpp"
+#include "emper-config.h"
 #include "io.hpp"
 
+#ifdef EMPER_HAS_COMPARE_H
+#include <compare>
+#endif
+
 const std::string HOST = "::";
 const std::string PORT = "12345";
 
+unsigned int computations_us = 0;
+
 auto main(int argc, char* argv[]) -> int {
 	std::string host = HOST;
 	std::string port = PORT;
 
-	if (argc > 2) {
-		std::cerr << "Usage: " << argv[0] << " [port]" << std::endl;
+	if (argc > 3) {
+		std::cerr << "Usage: " << argv[0] << " [port] [computation_us]" << std::endl;
 		exit(EXIT_FAILURE);
 	}
 
@@ -30,6 +38,10 @@ auto main(int argc, char* argv[]) -> int {
 		port = std::string(argv[1]);
 	}
 
+	if (argc > 2) {
+		computations_us = std::stoi(argv[2]);
+	}
+
 	std::cout << "Echoserver listening on " << host << ":" << port << std::endl;
 
 	Runtime runtime;
@@ -53,6 +65,14 @@ auto main(int argc, char* argv[]) -> int {
 				exit(EXIT_SUCCESS);
 			}
 
+			const auto start = std::chrono::steady_clock::now();
+			const auto deadline = start + std::chrono::microseconds(computations_us);
+			// TODO: The suppressed linter error below may be a false positive
+			// reported by clang-tidy.
+			// NOLINTNEXTLINE(modernize-use-nullptr)
+			while (std::chrono::steady_clock::now() < deadline) {
+			}
+
 			ssize_t bytes_send = emper::io::sendAndWait(socket, buf, bytes_recv, MSG_NOSIGNAL, true);
 			if (unlikely(bytes_recv != bytes_send)) {
 				LOGE("server send failed: " << strerror(errno));