testsAndMisc/meta/scripts/check_polling_antipatterns.sh

#!/bin/bash
# Pre-commit hook to detect polling script anti-patterns.
# Blocks commits of shell scripts that violate efficient polling best practices.
#
# Usage: check_polling_antipatterns.sh [files...]
# Exit codes: 0 = no issues, 1 = issues found

set -euo pipefail

errors=0
files_checked=0

# Patterns to detect (these are red flags for fork storms)
# These are regex patterns held literally -- the $( and ` inside them are
# part of what we search FOR, so they must not be expanded here.
# shellcheck disable=SC2034,SC2016
declare -A patterns=(
	['while_true_with_sleep']='while\s+(true|:).*sleep'
	['date_in_loop']='while.*date|for.*date'
	['pgrep_in_loop']='while.*pgrep|for.*pgrep'
	['xdotool_in_loop']='while.*xdotool|for.*xdotool'
	['pipe_fork_chain']='|.*|.*|.*|'
	['subshell_date']='$\(date\s+\+'
	['backtick_date']='`date\s+\+'
	['excessive_fork_chain']='(\$\(.*\|.*\|.*\)|`.*\|.*\|`)'
	['sleep_less_than_one']='sleep\s+0\.[0-9]'
)

usage() {
	echo "Usage: $(basename "$0") [files...]"
	echo ""
	echo "Checks shell scripts for polling anti-patterns that cause fork storms."
	echo "Exit code 0 = no issues, 1 = issues found"
	echo ""
	echo "Patterns detected:"
	echo "  - while true + sleep (should use event-driven I/O)"
	echo "  - \$(date +...) in loops (forks process)"
	echo "  - pgrep/xdotool in loops (forks process)"
	echo "  - Multiple piped commands (each | forks)"
	echo "  - Aggressive polling (sleep < 1s)"
	exit 0
}

check_file() {
	local file="$1"

	# Skip non-shell files
	if ! grep -qE '^#!.*/(ba)?sh' "$file" 2>/dev/null; then
		return 0
	fi

	files_checked=$((files_checked + 1))

	# Single-pass awk analysis: C code, no bash loops, no per-line subshell forks.
	# '\'' embeds a literal single quote inside a bash single-quoted string.
	local findings
	findings=$(awk '
        /^[[:space:]]*([a-zA-Z0-9_]*_(loop|daemon)|poll[a-zA-Z0-9_]*)[[:space:]]*\(\)/ { in_poll=1 }
        /^[[:space:]]*\}/ { in_poll=0 }
        in_poll {
            if (/while[[:space:]]+(true|:)/ && /sleep/)
                print NR ": while true/: + sleep (use event-driven I/O)"
            if (/\$\(date[[:space:]]/ || /`date[[:space:]]/)
                print NR ": date fork in polling function"
            if (/[^_a-zA-Z0-9]pgrep/ || /^[[:space:]]*pgrep/)
                print NR ": pgrep in polling context"
            if (/[^_a-zA-Z0-9]xdotool/ || /^[[:space:]]*xdotool/)
                print NR ": xdotool in polling context"
            if (/sleep[[:space:]]+0\.[0-9]/)
                print NR ": Aggressive polling (sleep < 1s)"
        }
        !/^[[:space:]]*#/ && !/=/ && !/\)[[:space:]]*(#.*)?$/ && !/;;/ {
            line = $0
            gsub(/\|\|/, "", line)
            while (match(line, /'\''[^'\'']*'\''/)) line = substr(line, 1, RSTART-1) substr(line, RSTART+RLENGTH)
            while (match(line, /"[^"]*"/)) line = substr(line, 1, RSTART-1) substr(line, RSTART+RLENGTH)
            n = gsub(/\|/, "", line)
            if (n > 3) print NR ": Excessive pipes (" n " pipes = many forks)"
        }
    ' "$file")

	if [[ -n "$findings" ]]; then
		echo "  $file:"
		while IFS= read -r finding; do
			echo "    Line $finding"
		done <<<"$findings"
		errors=$((errors + 1))
		return 1
	fi
	return 0
}
provide_suggestions() {
	echo ""
	echo "📋 Optimization Tips:"
	echo ""
	echo "Replace polling loops with:"
	echo "  • inotifywait/fanotify for file system events"
	echo "  • timerfd for interval-based tasks"
	echo "  • select/poll for I/O multiplexing"
	echo "  • systemd timers for scheduled tasks"
	echo "  • dbus signals for system events"
	echo ""
	echo "Reduce fork overhead:"
	echo "  • Cache \$(date +%s) in variable, update periodically"
	echo "  • Use /proc filesystem instead of pgrep"
	echo "  • Consolidate commands with && instead of separate invocations"
	echo ""
}

main() {
	# Show usage if requested
	[[ "$#" -eq 0 || "$1" == "-h" || "$1" == "--help" ]] && usage

	# Check all provided files
	for file in "$@"; do
		check_file "$file" || true
	done

	# Report results
	if [[ $files_checked -eq 0 ]]; then
		echo "ℹ️  No shell scripts to check"
		exit 0
	fi

	if [[ $errors -gt 0 ]]; then
		echo ""
		echo "❌ Found $errors issue(s) in shell scripts"
		provide_suggestions
		exit 1
	else
		echo "✓ No polling anti-patterns detected in $files_checked file(s)"
		exit 0
	fi
}

main "$@"