Add a test for thread-safe malloc

Add a test to repeatedly malloc and free from different threads to
test if these functions are thread safe.

Author: c1728p9

TESTS/mbedmicro-rtos-mbed/malloc/main.cpp

@@ -0,0 +1,68 @@
+#include "mbed.h"
+#include "test_env.h"
+#include "rtos.h"
+
+#if defined(MBED_RTOS_SINGLE_THREAD)
+  #error [NOT_SUPPORTED] test not supported
+#endif
+
+#define NUM_THREADS         5
+#define THREAD_STACK_SIZE   256
+
+DigitalOut led1(LED1);
+volatile bool should_exit = false;
+volatile bool allocation_failure = false;
+
+void task_using_malloc(void)
+{
+    void* data;
+    while (1) {
+        // Repeatedly allocate and free memory
+        data = malloc(100);
+        if (data != NULL) {
+            memset(data, 0, 100);
+        } else {
+            allocation_failure = true;
+        }
+        free(data);
+
+        if (should_exit) {
+            return;
+        }
+    }
+}
+
+int main()
+{
+    Thread *thread_list[NUM_THREADS];
+    int test_time = 15;
+    GREENTEA_SETUP(20, "default_auto");
+
+    // Allocate threads for the test
+    for (int i = 0; i < NUM_THREADS; i++) {
+        thread_list[i] = new Thread(osPriorityNormal, THREAD_STACK_SIZE);
+        if (NULL == thread_list[i]) {
+            allocation_failure = true;
+        }
+        thread_list[i]->start(task_using_malloc);
+    }
+
+    // Give the test time to run
+    while (test_time) {
+        led1 = !led1;
+        Thread::wait(1000);
+        test_time--;
+    }
+
+    // Join and delete all threads
+    should_exit = 1;
+    for (int i = 0; i < NUM_THREADS; i++) {
+        if (NULL == thread_list[i]) {
+            continue;
+        }
+        thread_list[i]->join();
+        delete thread_list[i];
+    }
+
+    GREENTEA_TESTSUITE_RESULT(!allocation_failure);
+}