tests: ssl: socket.sendall() busy loop when client is reading slowly

https://bitbucket.org/which_linden/eventlet/issue/134

tests/ssl_test.py

@@ -1,10 +1,10 @@
-from tests import LimitedTestCase, certificate_file, private_key_file
+from tests import LimitedTestCase, certificate_file, private_key_file, check_idle_cpu_usage
 from tests import skip_if_no_ssl
 from unittest import main
 import eventlet
-from eventlet import util, coros, greenio
+from eventlet import util, greenio
 import socket
-import os
+
 
 def listen_ssl_socket(address=('127.0.0.1', 0)):
     sock = util.wrap_ssl(socket.socket(), certificate_file,
@@ -93,6 +93,47 @@ class SSLTest(LimitedTestCase):
         client2.send('after')
         server_coro.wait()
 
+    @skip_if_no_ssl
+    def test_sendall_cpu_usage(self):
+        """SSL socket.sendall() busy loop
+
+        https://bitbucket.org/which_linden/eventlet/issue/134/greenssl-performance-issues
+
+        Idea of this test is to check that GreenSSLSocket.sendall() does not busy loop
+        retrying .send() calls, but instead trampolines until socket is writeable.
+
+        BUFFER_SIZE and SENDALL_SIZE are magic numbers inferred through trial and error.
+        """
+        # Time limit resistant to busy loops
+        self.set_alarm(1)
+
+        stage_1 = eventlet.event.Event()
+        BUFFER_SIZE = 1000
+        SENDALL_SIZE = 100000
+
+        def serve(listener):
+            conn, _ = listener.accept()
+            conn.setsockopt(socket.SOL_SOCKET, socket.SO_SNDBUF, BUFFER_SIZE)
+            self.assertEqual(conn.read(8), 'request')
+            conn.write('response')
+
+            stage_1.wait()
+            conn.sendall('x' * SENDALL_SIZE)
+
+        server_sock = listen_ssl_socket()
+        server_coro = eventlet.spawn(serve, server_sock)
+
+        client_sock = eventlet.connect(server_sock.getsockname())
+        client_sock.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, BUFFER_SIZE)
+        client = util.wrap_ssl(client_sock)
+        client.write('request')
+        self.assertEqual(client.read(8), 'response')
+        stage_1.send()
+
+        check_idle_cpu_usage(0.2, 0.1)
+        server_coro.kill()
+
+
 class SocketSSLTest(LimitedTestCase):
     @skip_if_no_ssl
     def test_greensslobject(self):