差分

このページの2つのバージョン間の差分を表示します。

--- softwares:nestdaq:cplusplus [2024/02/02 16:07] – [std::chrono ライブラリ] kobayash
+++ softwares:nestdaq:cplusplus [2024/02/02 16:19] (現在) – [std::chrono ライブラリ] kobayash
@@ 行 36: / 行 36: @@
   * 参考: Stack Overflow -- Different behaviour of system_clock on windows and linux https://stackoverflow.com/questions/55120594/different-behaviour-of-system-clock-on-windows-and-linux
 === std::chrono ライブラリクロックの違い ===
-  * 以下のようなコードを書く
+  * 以下のようなコードを書く<code>
-  * システムの時計をずれせるように、network の時刻同期を切る。<code>
+#include <iostream>
+#include <thread>
+#include <chrono>
+int main(int argc,char *argv[]){
+  std::chrono::system_clock::time_point          system_clock_start = std::chrono::system_clock::now();
+  std::chrono::steady_clock::time_point          steady_clock_start = std::chrono::steady_clock::now();
+  std::chrono::high_resolution_clock::time_point h_reso_clock_start = std::chrono::high_resolution_clock::now();
+  std::chrono::nanoseconds system_clock_start_epoch = std::chrono::duration_cast<std::chrono::nanoseconds> (system_clock_start.time_since_epoch());
+  std::chrono::nanoseconds steady_clock_start_epoch = std::chrono::duration_cast<std::chrono::nanoseconds> (steady_clock_start.time_since_epoch());
+  std::chrono::nanoseconds h_reso_clock_start_epoch = std::chrono::duration_cast<std::chrono::nanoseconds> (h_reso_clock_start.time_since_epoch());
+  for (int i = 0; i < 100; i++) {
+    std::chrono::system_clock::time_point          system_clock_now = std::chrono::system_clock::now();
+    std::chrono::steady_clock::time_point          steady_clock_now = std::chrono::steady_clock::now();
+    std::chrono::high_resolution_clock::time_point h_reso_clock_now = std::chrono::high_resolution_clock::now();
+    std::chrono::nanoseconds system_clock_now_epoch = std::chrono::duration_cast<std::chrono::nanoseconds> (system_clock_now.time_since_epoch());
+    std::chrono::nanoseconds steady_clock_now_epoch = std::chrono::duration_cast<std::chrono::nanoseconds> (steady_clock_now.time_since_epoch());
+    std::chrono::nanoseconds h_reso_clock_now_epoch = std::chrono::duration_cast<std::chrono::nanoseconds> (h_reso_clock_now.time_since_epoch());
+    std::chrono::nanoseconds system_clock_duration  = std::chrono::duration_cast<std::chrono::nanoseconds> (system_clock_now - system_clock_start);
+    std::chrono::nanoseconds steady_clock_duration  = std::chrono::duration_cast<std::chrono::nanoseconds> (steady_clock_now - steady_clock_start);
+    std::chrono::nanoseconds h_reso_clock_duration  = std::chrono::duration_cast<std::chrono::nanoseconds> (h_reso_clock_now - h_reso_clock_start);
+    std::time_t now = std::chrono::system_clock::to_time_t(system_clock_now);
+    std::string s(30, '\0');
+    std::strftime(&s[0], s.size(), "%Y-%m-%d %H:%M:%S", std::localtime(&now));
+    std::cout << "system_clock_now: " << s << std::endl;
+    std::cout << "system_clock_now_epoch.count(): " << system_clock_now_epoch.count() << std::endl;
+    std::cout << "steady_clock_now_epoch.count(): " << steady_clock_now_epoch.count() << std::endl;
+    std::cout << "h_reso_clock_now_epoch.count(): " << h_reso_clock_now_epoch.count() << std::endl;
+    std::cout << "system_clock_duration.count(): "  << system_clock_duration.count() << std::endl;
+    std::cout << "steady_clock_duration.count(): "  << steady_clock_duration.count() << std::endl;
+    std::cout << "h_reso_clock_duration.count(): "  << h_reso_clock_duration.count() << std::endl;
+    std::cout << std::endl;
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+  }
+  return 0;
+}
+</code>
+  * macOS 12.3.1 でシステムの時計をずらせるように、network の時刻同期を切る。<code>
 $ sudo systemsetup -setusingnetworktime off
 -02-02 15:09:51.126 systemsetup[23124:12338196] ### Error:-99 File:/AppleInternal/Library/BuildRoots/66382bca-8bca-11ec-aade-6613bcf0e2ee/Library/Caches/com.apple.xbs/Sources/Admin/InternetServices.m Line:379
 setUsingNetworkTime: Off
 </code>
-  * コードを実行する。<code>$ ./std_chrono_comp_clocks
+  * macOS 12.3.1 上でコードを実行する。<code>$ ./std_chrono_comp_clocks
 system_clock_now: 2024-02-02 15:56:02
 system_clock_now_epoch.count(): 1706856962044809000
@@ 行 96: / 行 138: @@
 steady_clock_duration.count(): 5021508219
 h_reso_clock_duration.count(): 5021508221
-</code>
+</code> これをみると、std::chrono::high_resolution_clock は std::chrono::steady_clock の別名のようだ。また、Ubuntu MATE 22.03.3 LTS で実行すると、以下のようになる。<code>
+$ ./std_chrono_comp_clocks
+system_clock_now: 2024-02-02 16:18:15
+system_clock_now_epoch.count(): 1706858295484039608
+steady_clock_now_epoch.count(): 1109260620490710
+h_reso_clock_now_epoch.count(): 1706858295484039845
+system_clock_duration.count(): 1217
+steady_clock_duration.count(): 958
+h_reso_clock_duration.count(): 945
+system_clock_now: 2024-02-02 16:18:16
+system_clock_now_epoch.count(): 1706858296484348873
+steady_clock_now_epoch.count(): 1109261620800102
+h_reso_clock_now_epoch.count(): 1706858296484349263
+system_clock_duration.count(): 1000310482
+steady_clock_duration.count(): 1000310350
+h_reso_clock_duration.count(): 1000310363
+system_clock_now: 2024-02-02 16:18:17
+system_clock_now_epoch.count(): 1706858297484600085
+steady_clock_now_epoch.count(): 1109262621051266
+h_reso_clock_now_epoch.count(): 1706858297484600429
+system_clock_duration.count(): 2000561694
+steady_clock_duration.count(): 2000561514
+h_reso_clock_duration.count(): 2000561529
+...
+</code> これを見ると、std::chrono::high_resolution_clock は std::chrono::system_clock の別名のようだ。
 ==== Arrow operator (->) in the function declaration ====