bitbake: tests: Add Timeout class

The class and exception aim to test rare cases there deadlocks are
possible.
Can be used in context managers:
with Timeout(<value>):
        do_deadlock()

(Bitbake rev: c5fcdd804d422f959a189b270d72123a50e74da6)

Signed-off-by: Pavel Zhukov <pavel@zhukoff.net>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/tests/fetch.py

@@ -11,6 +11,7 @@ import hashlib
 import tempfile
 import collections
 import os
+import signal
 import tarfile
 from bb.fetch2 import URI
 from bb.fetch2 import FetchMethod
@@ -22,6 +23,24 @@ def skipIfNoNetwork():
         return unittest.skip("network test")
     return lambda f: f
 
+class TestTimeout(Exception):
+    pass
+
+class Timeout():
+
+    def __init__(self, seconds):
+        self.seconds = seconds
+
+    def handle_timeout(self, signum, frame):
+        raise TestTimeout("Test failed: timeout reached")
+
+    def __enter__(self):
+        signal.signal(signal.SIGALRM, self.handle_timeout)
+        signal.alarm(self.seconds)
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        signal.alarm(0)
+
 class URITest(unittest.TestCase):
     test_uris = {
         "http://www.google.com/index.html" : {