Add IO sleep to agent forward communications.

Without this, use of agent forwarding causes
high CPU usage on some clients.
(cherry picked from commit 3030589aaa)

Conflicts:
	paramiko/agent.py

paramiko/__init__.py

@@ -103,6 +103,8 @@ from common import AUTH_SUCCESSFUL, AUTH_PARTIALLY_SUCCESSFUL, AUTH_FAILED, \
 from sftp import SFTP_OK, SFTP_EOF, SFTP_NO_SUCH_FILE, SFTP_PERMISSION_DENIED, SFTP_FAILURE, \
      SFTP_BAD_MESSAGE, SFTP_NO_CONNECTION, SFTP_CONNECTION_LOST, SFTP_OP_UNSUPPORTED
 
+from common import io_sleep
+
 __all__ = [ 'Transport',
             'SSHClient',
             'MissingHostKeyPolicy',
@@ -136,4 +138,5 @@ __all__ = [ 'Transport',
             'AgentKey',
             'HostKeys',
             'SSHConfig',
-            'util' ]
+            'util',
+            'io_sleep' ]

paramiko/agent.py

@@ -34,6 +34,7 @@ from paramiko.ssh_exception import SSHException
 from paramiko.message import Message
 from paramiko.pkey import PKey
 from paramiko.channel import Channel
+from paramiko.common import io_sleep
 
 SSH2_AGENTC_REQUEST_IDENTITIES, SSH2_AGENT_IDENTITIES_ANSWER, \
     SSH2_AGENTC_SIGN_REQUEST, SSH2_AGENT_SIGN_RESPONSE = range(11, 15)
@@ -134,6 +135,7 @@ class AgentProxyThread(threading.Thread):
                         self._agent._conn.send(data)
                     else:
                         break
+            time.sleep(io_sleep)
 
 class AgentLocalProxy(AgentProxyThread):
     """

paramiko/common.py

@@ -124,3 +124,6 @@ INFO = logging.INFO
 WARNING = logging.WARNING
 ERROR = logging.ERROR
 CRITICAL = logging.CRITICAL
+
+# Common IO/select/etc sleep period, in seconds
+io_sleep = 0.01