Update [10/15/2017]

It seems that Xcode 9.1 beta 2 fixes this issue.

In my preliminary testing, everything worked fine. This feels really good.

Original Article

There were recently two popular Swift posts on Hacker News^{1 2}, and one issue I saw coming up multiple times was the memory consumption of the tooling nee Xcode. One particular problem is that for some codebases the Swift sourcecode process SourceKitService consumes a huge amount of memory. I've had it rise to 30GB and beyond - at which point my system usually stalls and I'm not able to continue working for a couple of minutes.

Oftentimes memory issues like these can be solved by reviewing your sourcecode with the same tools you also use to reduce your compile times. See:

• https://www.jessesquires.com/blog/measuring-compile-times-xcode9/
• https://www.swiftbysundell.com/posts/improving-swift-compile-times

However, for some, complex, codebases this may not be enough. I've employed an awful little hack in order to at least keep my machine from stalling. I wrote a small little bash script that check the memory consumption of the SourceKitService every n seconds and if it goes beyond x megabytes of memory (by default 5.000) I restart it. I feel that this may be useful to some others so I'm sharing it here for posterity. Note that this is an awful hack and future versions of SourceKitService will probably (hopefully!) not need this anymore. Meanwhile, this might be of help to others:

#!/bin/bash

# Amount of seconds to wait between measures
n=1
# Limit memory consumption to this many megabytes before killing the process
x=5000

name="SourceKitService"
while true; do 
  fields=`ps aux -m | grep -v grep | grep -i $name | tr -s ' '`
  mem=`echo $fields | cut -d ' ' -s -f 6| awk '{$1=$1/1024; print $1;}' | cut -d '.' -f 1`
  pid=`echo $fields | cut -d ' ' -s -f 2`
  if [ -z "$mem" ]; then
      echo "$name not running"
      sleep 15
      continue
  fi
  if [ "$mem" -gt $x ]; then
      echo "Killing $name pid $pid with mem $mem"
      kill -9 $pid
      sleep 5
  fi
  sleep $n
done

To use this just paste that code into a file (say sourcekill.sh) and do:

chmod +x ./sourcekill.sh
./sourcekill.sh

If you want to kill it, just hit CTRL=C.