Adding unit test for reentrancy

tests/test_reent.cpp

@@ -0,0 +1,65 @@
+/*
+ *   test_reent.cpp
+ *
+ *   Created: 8/30/2018
+ *   Author: Michael E. Tryby
+ *           US EPA - ORD/NRMRL
+ *
+ *   Multi-threading / reentrancy test for EPANET Toolkit API.
+*/
+
+#include <string>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <boost/thread.hpp>
+
+#include "epanet2.h"
+
+#define NUM_THREADS 2
+
+using namespace std;
+
+void  epanet_thread(long i)
+{
+    int errorcode = 0;
+    EN_ProjectHandle ph;
+
+    string prefix = "example_";
+    string suffix = ".inp";
+    string input = prefix + to_string(static_cast<long long>(i)) + suffix;
+
+    suffix = ".rpt";
+    string report = prefix + to_string(static_cast<long long>(i)) + suffix;
+
+    suffix = ".out";
+    string output = prefix + to_string(static_cast<long long>(i)) + suffix;
+
+    printf("Thread #%ld starting EPANET ...\n", i);
+
+    EN_createproject(&ph);
+    errorcode = EN_runproject(ph, input.c_str(), report.c_str(), output.c_str(), NULL);
+    EN_deleteproject(&ph);
+
+    printf("Thread #%ld EPANET done. Status = %d\n", i, errorcode);
+}
+
+int main(int argc, char *argv[])
+{
+    long i;
+    boost::thread *threads[NUM_THREADS];
+
+    for (i = 0; i < NUM_THREADS; i++) {
+        threads[i] = new boost::thread(epanet_thread, i);
+        printf("Main: creating thread %ld.\n", i);
+    }
+
+    for (i = 0; i < NUM_THREADS; i++) {
+        threads[i]->join();
+        printf("Main: joining thread %ld.\n", i);
+        delete threads[i];
+    }
+
+    printf("Main: program completed. Exiting.\n");
+    return(0);
+}