Composer hanging while updating dependencies

So it turns out the problem was with php's xdebug extension. After disabling it in my php.ini, composer ran without any problems.

And just to note, the hang-up wasn't actually occurring while reading files from the cache. It was the step right after where composer was trying to resolve dependencies. It just never finished that step and never printed the output. That's why no matter what I did, it always appeared to be stuck reading a file from the cache.

In my case, it was simply taking a very long time on my 8GB ram Mac. To check the progress and verify that it is going through the dependencies, run composer in verbose mode. This was an approach I missed in the question so worth re-stating here.

composer update -vvv

Some times it is stuck because it is trying to use HTTP instead of https so just run this

composer config --global repo.packagist composer https://packagist.org

1st of all : Check firewall and proxy connections. If everything is ok but composer is still hanging try to clear composer cache:

composer clear-cache

https://getcomposer.org/doc/03-cli.md#clear-cache

2nd option If these steps does not repair your composer then it's possible that the system does not have enough RAM memory available (I faced this problem and the symptomps were the same that you describe). At this point you have two options:

a) Increase memory (Virtual Machines or Docker) : Your container or VM needs more available memory. Follow this guide: https://stackoverflow.com/a/44533437/3518053

b) Generate swap file (Linux) : Try creating a swap file to provide more memory: (Above commands are from composer killed while updating)

free -m
mkdir -p /var/_swap_
cd /var/_swap_
#Here, 1M * 2000 ~= 2GB of swap memory
dd if=/dev/zero of=swapfile bs=1M count=2000
mkswap swapfile
swapon swapfile
chmod 600 swapfile
echo "/var/_swap_/swapfile none swap sw 0 0" >> /etc/fstab
#cat /proc/meminfo
free -m