Why does dev_appserver.py use so much CPU even when idle?

Question

I am starting dev_appserver.py with the following parameters:

dev_appserver.py --require_indexes=yes --datastore_path=/Users/mattfaus/dev/webapp/datastore/current.sqlite --blobstore_path=/Users/mattfaus/dev/webapp/datastore/blobs/ --host=0.0.0.0 --port=8080 --skip_sdk_update_check=yes --enable_sendmail=yes /Users/mattfaus/dev/webapp

And in Activity Monitor I see that it is constantly using 150% CPU even when it is not servicing requests. The biggest symptom I see is drastically reduce battery life and a nearly overheating CPU on my Macbook Pro. I now have to be careful to shutdown the appserver any time I am not using it to prevent these things from happening.

This started happening about 1 month ago, probably when I upgraded to 1.8.1 or 1.8.2. Is there any way I can configure GAE to stop using so much CPU?

I am using GAE SDK 1.8.3 and here is an overview of my hardware/software.

Hardware Overview:

Model Name: MacBook Pro Model Identifier: MacBookPro9,1 Processor Name: Intel Core i7 Processor Speed: 2.3 GHz Number of Processors: 1 Total Number of Cores: 4 L2 Cache (per Core): 256 KB L3 Cache: 6 MB Memory: 16 GB Sudden Motion Sensor: State: Enabled

System Software Overview:

System Version: OS X 10.8.4 (12E55) Kernel Version: Darwin 12.4.0 Boot Volume: Macintosh HD Boot Mode: Normal Computer Name: mattfaus User Name: Matt Faus (mattfaus) Secure Virtual Memory: Enabled

Answer 1

The heavy cpu load you are observing on osx is caused by the file watcher that dev_appserver uses to monitor changes and restart instances automatically.

As you have noticed, using the parameter --automatic_restart=no solves the issue but it's not great while developing.

One solution is to replace the file watcher, for example using this one (specifically meant to address the issue) : https://github.com/nilleb/fsevents-watcher

See this article for more context information : https://medium.com/lumapps-engineering/appengine-on-macos-is-a-cpu-hog-heres-how-to-solve-this-problem-with-another-python-native-9f2a6dc5c960