No limit on concurrent go routines leads to error

[Chan9390]

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Checking the source code pillage.go I found the following flow:

EnumRegistries() --> EnumRegistry() --> EnumRepository() --> EnumImage()

Each stage executes asynchronously and crane gets called once when enumerating registry, repository and image.

So if I have 1 registry with 2 docker containers with 3 tags each, the code will have invoked crane 6 times. When dealing with huge registries, crane is invoked multiple times. Since crane uses docker credential file configured on the system its running, it returns the error open /Users/username/.docker/config.json: too many open files when invoked multiple times.