Added concurrency features to the progress bar

concurrent_example/Makefile

@@ -0,0 +1,12 @@
+CC = g++
+#---------------------------------------------------------
+CPPFLAGS=-I../include
+LDFLAGS=-pthread
+#---------------------------------------------------------
+MAIN="concurrent_example"
+#---------------------------------------------------------
+all: ${MAIN}
+
+${MAIN}: 
+	${CC} ${MAIN}.cpp -o ${MAIN} ${CPPFLAGS} ${LDFLAGS}
+

concurrent_example/concurrent_example.cpp

@@ -0,0 +1,53 @@
+#include <iostream>
+#include <unistd.h>
+#include <thread>
+#include "progresscpp/ProgressBar.hpp"
+
+/*
+ * Function which is thrown as thread
+ */
+void workerThread(int total, progresscpp::ProgressBar& progressBar) {
+    for (int i = 0; i < total; i++) {
+        ++progressBar; // record the tick
+
+        usleep(200); // simulate work
+
+        // display the bar only at certain steps
+        if (i % 10 == 0)
+            progressBar.display();
+    }
+}
+
+/* Example usage of ProgressBar by multiple threads */
+int main() {
+    const int partial = 1000;
+
+    /*
+     * Define a progress bar that has a total of 10000,
+     * a width of 70, shows `#` to indicate completion
+     * and a dash '-' for incomplete
+     */
+    progresscpp::ProgressBar progressBar(10 * partial, 70, '#', '-');
+
+    /*
+     * Throw ten threads which access the same ProgressBar 
+     * instance concurrently
+     */
+    std::thread workers[10];
+    for (int i = 0; i < 10; i++) {
+    	workers[i] = std::thread(workerThread, partial, std::ref(progressBar));
+    }
+
+    /*
+     * Wait for threads to finish the work
+     */
+    for (int i = 0; i < 10; i++) {
+    	workers[i].join();
+    }
+
+    // tell the bar to finish
+    progressBar.done();
+
+    std::cout << "Done!" << std::endl;
+    return 0;
+}

include/progresscpp/ProgressBar.hpp

@@ -2,11 +2,13 @@
 
 #include <chrono>
 #include <iostream>
+#include <mutex>
 
 namespace progresscpp {
 class ProgressBar {
 private:
     unsigned int ticks = 0;
+    mutable std::mutex mtx;
 
     const unsigned int total_ticks;
     const unsigned int bar_width;
@@ -20,7 +22,10 @@ class ProgressBar {
 
     ProgressBar(unsigned int total, unsigned int width) : total_ticks{total}, bar_width{width} {}
 
-    unsigned int operator++() { return ++ticks; }
+    unsigned int operator++() {
+    	std::unique_lock<std::mutex> lck (mtx);
+        return ++ticks;
+    }
 
     void display() const {
         float progress = (float) ticks / total_ticks;
@@ -29,6 +34,7 @@ class ProgressBar {
         std::chrono::steady_clock::time_point now = std::chrono::steady_clock::now();
         auto time_elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(now - start_time).count();
 
+    	std::unique_lock<std::mutex> lck (mtx); // stdout must be accessed in mutual exclusion
         std::cout << "[";
 
         for (int i = 0; i < bar_width; ++i) {