Added ^C handling to some examples for clean exits.

CHANGELOG.md

@@ -27,6 +27,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - The `properties` list implements a const iterator
 - Added a `to_string()` and `operator<<()` for reason codes.
 - Cleaned up and fixed a number of example apps.
+    - Most apps no except server URI from the command line
+    - 'data_publish' example uses C++17 std::filesystem for creating a file-based encrypted persistence for messages.
 - Reorganized the source repository
 - Completely reformat the sources and added a .clang-format file (a project master and a slightly-different one for headers).
 - Added GitHub CI Action, removing legacy Travis and Appveyor files

examples/async_publish_time.cpp

@@ -49,6 +49,8 @@
 #include <iostream>
 #include <string>
 #include <thread>  // For sleep
+#include <atomic>
+#include <csignal>
 
 #include "mqtt/async_client.h"
 
@@ -69,6 +71,14 @@ const int DELTA_MS = 100;
 // How many to buffer while off-line
 const int MAX_BUFFERED_MESSAGES = 1200;
 
+// Atomic flag to tell the main loop to exit.
+atomic<bool> quit{false};
+
+// Handler for ^C (SIGINT)
+void ctrlc_handler(int) {
+    quit = true;
+}
+
 // --------------------------------------------------------------------------
 // Gets the current time as the number of milliseconds since the epoch:
 // like a time_t with ms resolution.
@@ -130,14 +140,17 @@ int main(int argc, char* argv[])
         auto top = mqtt::topic(cli, "data/time", QOS);
         cout << "Publishing data..." << endl;
 
+        // Install a ^C handler for user to signal when to exit
+        signal(SIGINT, ctrlc_handler);
+
+        // Sync clock to start of delta period
         while (timestamp() % DELTA_MS != 0)
             ;
 
         uint64_t t = timestamp(), tlast = t, tstart = t;
-
         top.publish(to_string(t));
 
-        while (true) {
+        while (!quit) {
             this_thread::sleep_for(SAMPLE_PERIOD);
 
             t = timestamp();

examples/data_publish.cpp

@@ -52,6 +52,9 @@
 #include <thread>
 #include <filesystem>
 #include <fstream>
+#include <csignal>
+#include <mutex>
+#include <condition_variable>
 
 #include "mqtt/async_client.h"
 
@@ -77,6 +80,20 @@ const fs::path PERSIST_DIR{"persist"};
 // A key for encoding the persistence data
 const string PERSIST_KEY{"elephant"};
 
+// Condition variable & flag to tell the main loop to exit.
+std::condition_variable cv;
+std::mutex mtx;
+bool quit{false};
+
+// Handler for ^C (SIGINT)
+void ctrlc_handler(int) {
+    {
+        lock_guard<mutex> lk(mtx);
+        quit = true;
+    }
+    cv.notify_one();
+}
+
 /////////////////////////////////////////////////////////////////////////////
 
 // Example of user-based file persistence with a simple XOR encoding scheme.
@@ -108,7 +125,7 @@ class encoded_file_persistence : virtual public mqtt::iclient_persistence
     }
 
     // Gets the persistence file name for the supplied key.
-    fs::path path_name(const string& key) const { return dir_ /key; }
+    fs::path path_name(const string& key) const { return dir_ / key; }
 
 public:
     // Create the persistence object with the specified encoding key
@@ -138,7 +155,10 @@ public:
 
     // Close the persistent store that was previously opened.
     // Remove the persistence directory, if it's empty.
-    void close() override { fs::remove(dir_); }
+    void close() override {
+        fs::remove(dir_);
+        fs::remove(dir_.parent_path());
+    }
 
     // Clears persistence, so that it no longer contains any persisted data.
     // Just remove all the files from the persistence directory.
@@ -271,12 +291,18 @@ int main(int argc, char* argv[])
         char tmbuf[32];
         unsigned nsample = 0;
 
-        // The time at which to reads the next sample, starting now
-        auto tm = steady_clock::now();
+        // Install a ^C handler for user to signal when to exit
+        signal(SIGINT, ctrlc_handler);
 
-        while (true) {
-            // Pace the samples to the desired rate
-            this_thread::sleep_until(tm);
+        // The steady time at which to read the next sample
+        auto tm = steady_clock::now() + 250ms;
+
+        // Pace the sampling by letting the condition variable time out
+        // periodically. When 'cv' is signaled, it's time to quit.
+        unique_lock lk(mtx);
+
+        while (!cv.wait_until(lk, tm, []{ return quit; })) {
+            lk.unlock();
 
             // Get a timestamp and format as a string
             time_t t = system_clock::to_time_t(system_clock::now());
@@ -293,6 +319,7 @@ int main(int argc, char* argv[])
             top.publish(std::move(payload));
 
             tm += PERIOD;
+            lk.lock();
         }
 
         // Disconnect