2.6 KiB
Saranwrap
This is a convenient way of bundling code off into a separate process. If you are using python 2.6, the multiprocessing module probably suits your needs better than saranwrap will.
The simplest way to use saranwrap is to wrap a module and then call functions on that module:
>>> from eventlet import saranwrap
>>> import time
>>> s_time = saranwrap.wrap(time)
>>> timeobj = s_time.gmtime(0)
>>> timeobj
saran:(1970, 1, 1, 0, 0, 0, 3, 1, 0)
>>> timeobj.tm_sec
0The objects so wrapped behave as if they are resident in the current process space, but every attribute access and function call is passed over a nonblocking pipe to the child process. For efficiency, it's best to make as few attribute calls as possible relative to the amount of work being delegated to the child process.
eventlet.saranwrap
Underlying Protocol
Saranwrap's remote procedure calls are achieved by intercepting the basic getattr and setattr calls in a client proxy, which commnicates those down to the server which will dispatch them to objects in it's process space.
The basic protocol to get and set attributes is for the client proxy to issue the command:
getattr $id $name setattr $id $name $value
getitem $id $item setitem $id $item $value eq $id $rhs del $id
When the get returns a callable, the client proxy will provide a callable proxy which will invoke a remote procedure call. The command issued from the callable proxy to server is:
call $id $name $args $kwargs
If the client supplies an id of None, then the get/set/call is applied to the object(s) exported from the server.
The server will parse the get/set/call, take the action indicated, and return back to the caller one of:
value $val callable object $id exception $excp
To handle object expiration, the proxy will instruct the rpc server to discard objects which are no longer in use. This is handled by catching proxy deletion and sending the command:
del $id
The server will handle this by removing clearing it's own internal references. This does not mean that the object will necessarily be cleaned from the server, but no artificial references will remain after successfully completing. On completion, the server will return one of:
value None exception $excp
The server also accepts a special command for debugging purposes:
status
Which will be intercepted by the server to write back:
status {...}
The wire protocol is to pickle the Request class in this file. The request class is basically an action and a map of parameters'