API in a nutshell¶
execnet ad-hoc instantiates local and remote Python interpreters. Each interpreter is accessible through a Gateway which manages code and data communication. Channels allow to exchange data between the local and the remote end. Groups help to manage creation and termination of sub interpreters.
Gateways: bootstrapping Python interpreters¶
All Gateways are instantiated via a call to
passing it a gateway specification or URL.
create and configure a gateway to a Python interpreter. The
specstring encodes the target gateway type and configuration information. The general format is:
If you leave out the
=valuepart a True value is assumed. Valid types:
socket=host:port. Valid configuration:
id=<string> specifies the gateway id python=<path> specifies which python interpreter to execute execmodel=model 'thread', 'eventlet', 'gevent' model for execution chdir=<path> specifies to which directory to change nice=<path> specifies process priority of new process env:NAME=value specifies a remote environment variable setting.
If no spec is given, self.defaultspec is used.
Here is an example which instantiates a simple Python subprocess:
>>> gateway = execnet.makegateway()
examples for valid gateway specifications¶
ssh=wyvern//python=python3.3//chdir=mycachespecifies a Python3.3 interpreter on the host
wyvern. The remote process will have
mycacheas its current working directory.
ssh=-p 5000 myhostmakes execnet pass “-p 5000 myhost” arguments to the underlying ssh client binary, effectively specifying a custom port.
popen//python=python2.6//nice=20specification of a python subprocess using the
python2.6executable which must be discoverable through the system
PATH; running with the lowest CPU priority (“nice” level). By default current dir will be the current dir of the instantiator.
popen//dont_write_bytecodeuses the same executable as the current Python, and also passes the
-Bflag on startup, which tells Python not write
.pyofiles. Note that this only works under CPython 2.6 and newer.
popen//env:NAME=valuespecifies a subprocess that uses the same interpreter as the one it is initiated from and additionally remotely sets an environment variable
popen//execmodel=eventletspecifies a subprocess that uses the same interpreter as the one it is initiated from but will run the other side using eventlet for handling IO and dispatching threads.
socket=192.168.1.4:8888specifies a Python Socket server process that listens on
remote_exec: execute source code remotely¶
All gateways offer a simple method to execute source code in the instantiated subprocess-interpreter:
return channel object and connect it to a remote execution thread where the given
sourceis a string: execute source string remotely with a
channelput into the global namespace.
sourceis a pure function: serialize source and call function with
**kwargs, adding a
channelobject to the keyword arguments.
sourceis a pure module: execute source of module with a
channelin its global namespace
In all cases the binding
__name__='__channelexec__'will be available in the global namespace of the remotely executing code.
It is allowed to pass a module object as source code
in which case it’s source code will be obtained and
get sent for remote execution.
a channel object whose symmetric counterpart channel
is available to the remotely executing source.
reconfigures the string-coercion behaviour of the gateway
Channels: exchanging data with remote code¶
A channel object allows to send and receive data between two asynchronously running programs.
sends the given item to the other side of the channel, possibly blocking if the sender queue is full. The item must be a simple python type and will be copied to the other side by value. IOError is raised if the write pipe was prematurely closed.
receive a data item that was sent from the other side. timeout: None [default] blocked waiting. A positive number indicates the number of seconds after which a channel.TimeoutError exception will be raised if no item was received. Note that exceptions from the remotely executing code will be reraised as channel.RemoteError exceptions containing a textual representation of the remote traceback.
set a callback function for receiving items.
All already queued items will immediately trigger the callback. Afterwards the callback will execute in the receiver thread for each received data item and calls to
receive()will raise an error. If an endmarker is specified the callback will eventually be called with the endmarker when the channel closes.
return a file-like object. mode can be ‘w’ or ‘r’ for writeable/readable files. if proxyclose is true file.close() will also close the channel.
close down this channel with an optional error message. Note that closing of a channel tied to remote_exec happens automatically at the end of execution and cannot be done explicitely.
wait until this channel is closed (or the remote side otherwise signalled that no more data was being sent). The channel may still hold receiveable items, but not receive any more after waitclose() has returned. Exceptions from executing code on the other side are reraised as local channel.RemoteErrors. EOFError is raised if the reading-connection was prematurely closed, which often indicates a dying process. self.TimeoutError is raised after the specified number of seconds (default is None, i.e. wait indefinitely).
RemoteError= <class 'execnet.gateway_base.RemoteError'>¶
TimeoutError= <class 'execnet.gateway_base.TimeoutError'>¶
Grouped Gateways and robust termination¶
All created gateway instances are part of a group. If you
execnet.makegateway it actually is forwarded to
execnet.default_group. Group objects are container
objects (see group examples)
and manage the final termination procedure:
trigger exit of member gateways and wait for termination of member gateways and associated subprocesses. After waiting timeout seconds try to to kill local sub processes of popen- and ssh-gateways. Timeout defaults to None meaning open-ended waiting and no kill attempts.
This method is implicitely called for each gateway group at
process-exit, using a small timeout. This is fine
for interactive sessions or random scripts which
you rather like to error out than hang. If you start many
processes then you often want to call
yourself and specify a larger or not timeout.
threading models: gevent, eventlet, thread¶
New in version 1.2: (status: experimental!)
execnet supports “thread”, “eventlet” and “gevent” as thread models on each of the two sides. You need to decide which model to use before you create any gateways:
# content of threadmodel.py import execnet # locally use "eventlet", remotely use "thread" model execnet.set_execmodel("eventlet", "thread") gw = execnet.makegateway() print (gw) print (gw.remote_status()) print (gw.remote_exec("channel.send(1)").receive())
You need to have eventlet installed in your environment and then you can execute this little test file:
$ python threadmodel.py <Gateway id='gw0' receive-live, eventlet model, 0 active channels> <RInfo 'numchannels=0, numexecuting=0, execmodel=thread'> 1
With python3 you can (as of December 2013) only use the thread model because neither eventlet-0.14.0 nor gevent-1.0 support Python3. When they start to support Python3, execnet will probably just work because it is itself Python3 compatible.
How to execute in the main thread¶
When the remote side of a gateway uses the ‘thread’ model, execution will preferably run in the main thread. This allows GUI loops or other code to behave correctly. If you, however, start multiple executions concurrently, they will run in non-main threads.
remote_status: get low-level execution info¶
All gateways offer a simple method to obtain some status information from the remote side.
return information object about remote execution status.
Calling this method tells you e.g. how many execution tasks are queued, how many are executing and how many channels are active.
rsync: synchronise filesystem with remote¶
execnet implements a simple efficient rsyncing protocol.
Here is a basic example for using RSync:
rsync = execnet.RSync('/tmp/source') gw = execnet.makegateway() rsync.add_target(gw, '/tmp/dest') rsync.send()
And here is API info about the RSync class.
RSync(sourcedir, callback=None, verbose=True)¶
This class allows to send a directory structure (recursively) to one or multiple remote filesystems.
There is limited support for symlinks, which means that symlinks pointing to the sourcetree will be send “as is” while external symlinks will be just copied (regardless of existance of such a path on remote side).
add_target(gateway, destdir, finishedcallback=None, **options)¶
Adds a remote target specified via a gateway and a remote destination directory.
Sends a sourcedir to all added targets. Flag indicates whether to raise an error or return in case of lack of targets
By setting the environment variable
EXECNET_DEBUG you can
configure a tracing mechanism:
|write per-process trace-files to
|perform tracing to stderr (popen-gateway slaves will send this to their instantiator)|
cross-interpreter serialization of python objects¶
New in version 1.1.
Execnet exposes a function pair which you can safely use to store and load values from different Python interpreters (e.g. Python2 and Python3, PyPy and Jython). Here is a basic example:
>>> import execnet >>> dump = execnet.dumps([1,2,3]) >>> execnet.loads(dump) [1,2,3]
For more examples see Dumping and loading values across interpreter versions.
return a serialized bytestring of the given obj.
The obj and all contained objects must be of a builtin python type (so nested dicts, sets, etc. are all ok but not user-level instances).
return the object as deserialized from the given bytestring.
- py2str_as_py3str: if true then string (str) objects previously
- dumped on Python2 will be loaded as Python3 strings which really are text objects.
- py3str_as_py2str: if true then string (str) objects previously
- dumped on Python3 will be loaded as Python2 strings instead of unicode objects.
if the bytestring was dumped with an incompatible protocol version or if the bytestring is corrupted, the
execnet.DataFormatErrorwill be raised.