5.7 KiB
Basic Usage
If it's your first time to Eventlet, you may find the illuminated
examples in the design-patterns document to be a good starting
point.
Eventlet is built around the concept of green threads (i.e. coroutines, we use the terms interchangeably) that are launched to do network-related work. Green threads differ from normal threads in two main ways:
- Green threads are so cheap they are nearly free. You do not have to conserve green threads like you would normal threads. In general, there will be at least one green thread per network connection.
- Green threads cooperatively yield to each other instead of preemptively being scheduled. The major advantage from this behavior is that shared data structures don't need locks, because only if a yield is explicitly called can another green thread have access to the data structure. It is also possible to inspect primitives such as queues to see if they have any pending data.
Primary API
The design goal for Eventlet's API is simplicity and readability. You should be able to read its code and understand what it's doing. Fewer lines of code are preferred over excessively clever implementations. Like Python itself, there should be one, and only one obvious way to do it in Eventlet!
Though Eventlet has many modules, much of the most-used stuff is
accessible simply by doing import eventlet. Here's a quick
summary of the functionality available in the eventlet
module, with links to more verbose documentation on each.
Greenthread Spawn
eventlet.spawn(func, args,*kw)
This launches a greenthread to call func. Spawning off
multiple greenthreads gets work done in parallel. The return value from
spawn is a greenthread.GreenThread object, which can be used to
retrieve the return value of func. See spawn <eventlet.greenthread.spawn> for more
details.
eventlet.spawn_n(func, args,*kw)
The same as spawn,
but it's not possible to know how the function terminated (i.e. no
return value or exceptions). This makes execution faster. See spawn_n <eventlet.greenthread.spawn_n> for more
details.
eventlet.spawn_after(seconds, func, args,*kw)
Spawns func after seconds have elapsed; a delayed
version of spawn. To
abort the spawn and prevent func from being called, call GreenThread.cancel on the
return value of spawn_after. See spawn_after <eventlet.greenthread.spawn_after>
for more details.
Greenthread Control
eventlet.sleep(seconds=0)
Suspends the current greenthread and allows others a chance to
process. See sleep <eventlet.greenthread.sleep> for more
details.
Pools control concurrency. It's very common in applications to want
to consume only a finite amount of memory, or to restrict the amount of
connections that one part of the code holds open so as to leave more for
the rest, or to behave consistently in the face of unpredictable input
data. GreenPools provide this control. See GreenPool <eventlet.greenpool.GreenPool> for
more on how to use these.
GreenPile objects represent chunks of work. In essence a GreenPile is
an iterator that can be stuffed with work, and the results read out
later. See GreenPile <eventlet.greenpool.GreenPile> for
more details.
Queues are a fundamental construct for communicating data between
execution units. Eventlet's Queue class is used to communicate between
greenthreads, and provides a bunch of useful features for doing that.
See Queue <eventlet.queue.Queue> for more
details.
This class is a way to add timeouts to anything. It raises
exception in the current greenthread after timeout
seconds. When exception is omitted or None, the
Timeout instance itself is raised.
Timeout objects are context managers, and so can be used in with
statements. See Timeout <eventlet.timeout.Timeout> for more
details.
Patching Functions
eventlet.import_patched(modulename, additional_modules,*kw_additional_modules)
Imports a module in a way that ensures that the module uses "green"
versions of the standard library modules, so that everything works
nonblockingly. The only required argument is the name of the module to
be imported. For more information see import-green.
eventlet.monkey_patch(all=True, os=False, select=False, socket=False, thread=False, time=False)
Globally patches certain system modules to be greenthread-friendly.
The keyword arguments afford some control over which modules are
patched. If all is True, then all modules are patched
regardless of the other arguments. If it's False, then the rest of the
keyword arguments control patching of specific subsections of the
standard library. Most patch the single module of the same name (os,
time, select). The exceptions are socket, which also patches the ssl
module if present; and thread, which patches thread, threading, and
Queue. It's safe to call monkey_patch multiple times. For more
information see monkey-patch.
Network Convenience Functions
eventlet.connect
eventlet.listen
eventlet.wrap_ssl
eventlet.serve
eventlet.StopServe
These are the basic primitives of Eventlet; there are a lot more out
there in the other Eventlet modules; check out the modules.