tests/thread: Add test for concurrent mutating of user instance.

tests/thread/mutate_instance.py

+# test concurrent mutating access to a shared user instance
+#
+# MIT license; Copyright (c) 2016 Damien P. George on behalf of Pycom Ltd
+
+import _thread
+
+# the shared user class and instance
+class User:
+    def __init__(self):
+        self.a = 'A'
+        self.b = 'B'
+        self.c = 'C'
+user = User()
+
+# main thread function
+def th(n, lo, hi):
+    for repeat in range(n):
+        for i in range(lo, hi):
+            setattr(user, 'attr_%u' % i, repeat + i)
+            assert getattr(user, 'attr_%u' % i) == repeat + i
+
+    with lock:
+        global n_finished
+        n_finished += 1
+
+lock = _thread.allocate_lock()
+n_repeat = 30
+n_range = 300
+n_thread = 4
+n_finished = 0
+
+# spawn threads
+for i in range(n_thread):
+    _thread.start_new_thread(th, (n_repeat, i * n_range, (i + 1) * n_range))
+
+# busy wait for threads to finish
+while n_finished < n_thread:
+    pass
+
+# check user instance has correct contents
+print(user.a, user.b, user.c)
+for i in range(n_thread * n_range):
+    assert getattr(user, 'attr_%u' % i) == n_repeat - 1 + i