actionlint causes pipe: too many open files or hangs when checking so many files

[rhysd]

Environment

• actionlint: 3c86c33
• OS: macOS 10.15
• Go 1.16

Repro

Check many workflows or large workflow:

actionlint ./testdata/realworld/*.yml

Expected behavior

actionlint runs as usual; runs without any output or reports some errors in workflows.

Actual behavior

actionlint dies with message:

`/usr/local/bin/shellcheck --norc -f json -x --shell bash -e SC1091,SC2194 -` did not run successfully while checking script at line:463,col:9: pipe: too many open files: error while checking ./testdata/realworld/diem_diem_.github_workflows_ci-test.yml

or hangs.

Investigation

actionlint runs checks in parallel thanks to Go's goroutine:

• each files are checked in parallel
• processes for external linters to check each run: are run in parallel

This works fine and makes actionlint much faster when the target size is small. But running so many processes in parallel consumes OS resource (in this case, it hit limit for number of files to open). And running process sometimes hangs on macOS though I don't know the reason.