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content/blog/gevent.md

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+---
+title: "Gevent"
+date: 2020-04-09T17:22:52-04:00
+draft: false
+tags: ["python", "concurrency"]
+---
+
+In my last post I spoke about [concurrency with asyncio](https://brandonrozek.com/blog/pyasyncio/). Now what if you don't want to concern yourself with async/await practices and just want to write synchronous code that executes I/O asynchronously?  That's where the library [gevent](http://www.gevent.org/) comes in. It does this by modifying Python's standard library during runtime to call it's own asynchronous versions.
+
+Last post code's example written in `gevent`.
+
+```python
+# The first two lines must be called before
+# any other modules are loaded
+import gevent
+from gevent import monkey; monkey.patch_all()
+
+import time
+
+def think(duration):
+    print("Starting to think for " + str(duration) + " seconds...")
+    time.sleep(duration)
+    print("Finished thinking for " + str(duration) + " seconds...")
+
+gevent.wait([
+    gevent.spawn(think, 5),
+    gevent.spawn(think, 2)
+])
+```
+
+Notice that the function `think` is written the same as the synchronous version. 
+
+`gevent` is written on top of C libraries `libev` or `libuv` . This combined with the monkey patching can make `gevent` based applications hard to debug if something goes wrong. Otherwise it's a great tool to quickly take advantage of concurrency.