pthread: Initial version of thread API

components/pthread/test/test_pthread_cxx.cpp

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+#include <iostream>
+#include <thread>
+#include <mutex>
+#include "unity.h"
+#include "rom/ets_sys.h"
+
+std::shared_ptr<int> global_sp;
+std::mutex mtx;
+
+void thread_main() {
+    int i = 0;
+    //std::cout << "thread_main!" << std::endl;
+    ets_printf("thread_main\n");
+
+    while (1) {
+        // std::cout << "thread_main " << i << std::endl;
+        ets_printf("thread_main %d\n", i);
+        i++;
+    }
+    // auto local_sp = global_sp;  // OK, copy constructor's parameter is reference-to-const
+
+    // int i = *global_sp;         // OK, operator* is const
+    // int j = *local_sp;          // OK, does not operate on global_sp
+
+    // *global_sp = 2;          // NOT OK, modifies int visible to other threads
+    // *local_sp = 2;           // NOT OK, modifies int visible to other threads
+
+    // mtx.lock();
+    // global_sp.reset();       // NOT OK, reset is non-const
+    // mtx.unlock();
+    //local_sp.reset();           // OK, does not operate on global_sp
+}
+
+//extern "C"
+TEST_CASE("pthread CXX test 1", "[pthread]")
+{
+    std::cout << "Hello world!" << std::endl;
+
+    global_sp.reset(new int(1));
+    std::thread t1(thread_main);
+    // std::thread t2(thread_main);
+    t1.join();
+    // t2.join();
+}