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This article introduces the relevant knowledge of "how to execute Gevent synchronously and asynchronously". In the operation process of actual cases, many people will encounter such difficulties. Next, let Xiaobian lead you to learn how to deal with these situations! I hope you can read carefully and learn something!

gevent is a libev-based concurrency library. It provides a neat API for a variety of concurrent and network-related tasks.

Greenlets

The main pattern used in gevent is Greenlet, a lightweight coroutine that plugs into Python as a C extension module. Greenlets all run inside the main operating system process, but they are cooperatively scheduled.

At any given moment, only one coroutine is running.

This is different from libraries such as multiprocessing or threading that provide true parallel construction. These libraries rotate processes and threads using operating system scheduling, which is true parallelism.

Synchronous and asynchronous execution

The core idea of concurrency is that large tasks can be broken down into a series of subtasks that can be scheduled to execute simultaneously or asynchronously, rather than one at a time or synchronously. Switching between two subtasks is also known as context switching.

In gevent, context switching is accomplished through yielding. In the example below, we have two contexts, each yielding to the other by calling gevent.sleep(0).

import gevent

def foo(): print('Running in foo') gevent.sleep(0)

print('Explicit context switch to foo again')

def bar(): print('Explicit context to bar') gevent.sleep(0)

print('Implicit context switch back to bar')gevent.joinall([ gevent.spawn(foo), gevent.spawn(bar),])Running in fooExplicit context to barExplicit context switch to foo againImplicit context switch back to bar

The following figure visualizes control flow as if stepping through an entire program in a debugger to illustrate how context switching occurs.

When we use gevent in network or IO-bound functions, these functions are scheduled collaboratively, and the true power of gevent comes into play. Gevent handles all the details to ensure that your network library implicitly hands over execution of the greenlet context when possible. Such a usage cannot be overemphasized. Or let's give some examples to illustrate.

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