Basic Usage

If it’s your first time to Evy, you may find the illuminated examples in the Design Patterns document to be a good starting point.

Evy 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 Evy’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 Evy!

Though Evy has many modules, much of the most-used stuff is accessible simply by doing import evy. Here’s a quick summary of the functionality available in the evy module, with links to more verbose documentation on each.

Greenthread Spawn

evy.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 for more details.

evy.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 for more details.

evy.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 for more details.

Greenthread Control


Suspends the current greenthread and allows others a chance to process. See sleep for more details.

class evy.GreenPool

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 for more on how to use these.

class evy.GreenPile

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 for more details.

class evy.Queue

Queues are a fundamental construct for communicating data between execution units. Evy’s Queue class is used to communicate between greenthreads, and provides a bunch of useful features for doing that. See Queue for more details.

class evy.Timeout

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 for more details.

Patching Functions

evy.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.

evy.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 Monkeypatching the Standard Library.

Network Convenience Functions

These are the basic primitives of Evy; there are a lot more out there in the other Evy modules; check out the Module Reference.

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